We introduce the distinction between slow and fast commands since those
are two different sources of latency. An O(1) or O(log N) command without
side effects (can't trigger deletion of large objects as a side effect of
its execution) if delayed is a symptom of inherent latency of the system.
A non-fast command (commands that may run large O(N) computations) if
delayed may just mean that the user is executing slow operations.
The advices LATENCY should provide in this two different cases are
different, so we log the two classes of commands in a separated way.
This fixes detection of wrong subcommand (that resulted in the default
all-commands output instead) and allows COMMAND INFO to be called
without arguments (resulting into an empty array) which is useful in
programmtically generated calls like the following (in Ruby):
redis.commands("command","info",*mycommands)
Note: mycommands may be empty.
Static was removed since it is needed in order to get symbols in stack
traces. Minor changes in the source code were operated to make it more
similar to the existing Redis code base.
COMMANDS returns a nested multibulk reply for each
command in the command table. The reply for each
command contains:
- command name
- arity
- array of command flags
- start key position
- end key position
- key offset step
- optional: if the keys are not deterministic and
Redis uses an internal key evaluation function,
the 6th field appears and is defined as a status
reply of: REQUIRES ARGUMENT PARSING
Cluster clients need to know where the keys are in each
command to implement proper routing to cluster nodes.
Redis commands can have multiple keys, keys at offset steps, or other
issues where you can't always assume the first element after
the command name is the cluster routing key.
Using the information exposed by COMMANDS, client implementations
can have live, accurate key extraction details for all commands.
Also implements COMMANDS INFO [commands...] to return only a
specific set of commands instead of all 160+ commands live in Redis.
Technically the problem is due to the client type API that does not
return a special value for the master, however fixing it locally in the
CLIENT KILL command is better currently because otherwise we would
introduce a new output buffer limit class as a side effect.
From mailing list post https://groups.google.com/forum/#!topic/redis-db/D3k7KmJmYgM
In the file “config.h”, the definition HAVE_ATOMIC is used to indicate
if an architecture on which redis is implemented supports atomic
synchronization primitives. Powerpc supports atomic synchronization
primitives, however, it is not listed as one of the architectures
supported in config.h. This patch adds the __powerpc__ to the list of
architectures supporting these primitives. The improvement of redis
due to the atomic synchronization on powerpc is significant,
around 30% to 40%, over the default implementation using pthreads.
This proposal adds __powerpc__ to the list of architectures designated
to support atomic builtins.
From mailing list post https://groups.google.com/forum/#!topic/redis-db/QLjiQe4D7LA
In zmalloc.c the following primitives are currently used
to synchronize access to single global variable:
__sync_add_and_fetch
__sync_sub_and_fetch
In some architectures such as powerpc these primitives are overhead
intensive. More efficient C11 __atomic builtins are available with
newer GCC versions, see
http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/_005f_005fatomic-Builtins.html#_005f_005fatomic-Builtins
By substituting the following __atomic… builtins:
__atomic_add_fetch
__atomic_sub_fetch
the performance improvement on certain architectures such as powerpc can be significant,
around 10% to 15%, over the implementation using __sync builtins while there is only slight uptick on
Intel architectures because it was already enforcing Intel Strongly ordered memory semantics.
The selection of __atomic built-ins can be predicated on the definition of ATOMIC_RELAXED
which Is available on in gcc 4.8.2 and later versions.
While we have to output failing masters in order to provide an accurate
map (that may be the one of a Redis Cluster in down state because not
all slots are served by a working master), to provide slaves in FAIL
state is not a good idea since those are not necesarely needed, and the
client will likely incur into a latency penalty trying to connect with a
slave which is down.
Note that this means that CLUSTER SLOTS does not provide a *complete*
map of slaves, however this would not be of any help since slaves may be
added later, and a client that needs to scale reads and requires to
stay updated with the list of slaves, need to do a refresh of the map
from time to time, anyway.
CLUSTER SLOTS returns a Redis-formatted mapping from
slot ranges to IP/Port pairs serving that slot range.
The outer return elements group return values by slot ranges.
The first two entires in each result are the min and max slots for the range.
The third entry in each result is guaranteed to be either
an IP/Port of the master for that slot range - OR - null
if that slot range, for some reason, has no master
The 4th and higher entries in each result are replica instances
for the slot range.
Output comparison:
127.0.0.1:7001> cluster nodes
f853501ec8ae1618df0e0f0e86fd7abcfca36207 127.0.0.1:7001 myself,master - 0 0 2 connected 4096-8191
5a2caa782042187277647661ffc5da739b3e0805 127.0.0.1:7005 slave f853501ec8ae1618df0e0f0e86fd7abcfca36207 0 1402622415859 6 connected
6c70b49813e2ffc9dd4b8ec1e108276566fcf59f 127.0.0.1:7007 slave 26f4729ca0a5a992822667fc16b5220b13368f32 0 1402622415357 8 connected
2bd5a0e3bb7afb2b56a2120d3fef2f2e4333de1d 127.0.0.1:7006 slave 32adf4b8474fdc938189dba00dc8ed60ce635b0f 0 1402622419373 7 connected
5a9450e8279df36ff8e6bb1c139ce4d5268d1390 127.0.0.1:7000 master - 0 1402622418872 1 connected 0-4095
32adf4b8474fdc938189dba00dc8ed60ce635b0f 127.0.0.1:7002 master - 0 1402622419874 3 connected 8192-12287
5db7d05c245267afdfe48c83e7de899348d2bdb6 127.0.0.1:7004 slave 5a9450e8279df36ff8e6bb1c139ce4d5268d1390 0 1402622417867 5 connected
26f4729ca0a5a992822667fc16b5220b13368f32 127.0.0.1:7003 master - 0 1402622420877 4 connected 12288-16383
127.0.0.1:7001> cluster slots
1) 1) (integer) 0
2) (integer) 4095
3) 1) "127.0.0.1"
2) (integer) 7000
4) 1) "127.0.0.1"
2) (integer) 7004
2) 1) (integer) 12288
2) (integer) 16383
3) 1) "127.0.0.1"
2) (integer) 7003
4) 1) "127.0.0.1"
2) (integer) 7007
3) 1) (integer) 4096
2) (integer) 8191
3) 1) "127.0.0.1"
2) (integer) 7001
4) 1) "127.0.0.1"
2) (integer) 7005
4) 1) (integer) 8192
2) (integer) 12287
3) 1) "127.0.0.1"
2) (integer) 7002
4) 1) "127.0.0.1"
2) (integer) 7006
Instead of having an hardcoded IP address in the node configuration, we
autodiscover it via MEET messages for automatic update when the node is
restarted with a different IP address.
This mechanism was discussed in the context of PR #1782.
Some deployments need traffic sent from a specific address. This
change uses the same policy as Cluster where the first listed bindaddr
becomes the source address for outgoing Sentinel communication.
Fixes#1667
Eventual configuration convergence is guaranteed by our periodic hello
messages to all the instances, however when there are important notices
to share, better make a phone call. With this commit we force an hello
message to other Sentinal and Redis instances within the next 100
milliseconds of a config update, which is practically better than
waiting a few seconds.
Lack of check of the SRI_PROMOTED flag caused Sentienl to act with the
promoted slave turned into a master during failover like if it was a
normal instance.
Normally this problem was not apparent because during real failovers the
old master is down so the bugged code path was not entered, however with
manual failovers via the SENTINEL FAILOVER command, the problem was
easily triggered.
This commit prevents promoted slaves from getting reconfigured, moreover
we now explicitly check that during a failover the slave turning into a
master is the one we selected for promotion and not a different one.
This implements the new Sentinel-Client protocol for the Sentinel part:
now instances are reconfigured using a transaction that ensures that the
config is rewritten in the target instance, and that clients lose the
connection with the instance, in order to be forced to: ask Sentinel,
reconnect to the instance, and verify the instance role with the new
ROLE command.
This will be used by CLIENT KILL and is also a good way to ensure a
given client is still the same across CLIENT LIST calls.
The output of CLIENT LIST was modified to include the new ID, but this
change is considered to be backward compatible as the API does not imply
you can do positional parsing, since each filed as a different name.
Because of output buffer limits Redis internals had this idea of type of
clients: normal, pubsub, slave. It is possible to set different output
buffer limits for the three kinds of clients.
However all the macros and API were named after output buffer limit
classes, while the idea of a client type is a generic one that can be
reused.
This commit does two things:
1) Rename the API and defines with more general names.
2) Change the class of clients executing the MONITOR command from "slave"
to "normal".
"2" is a good idea because you want to have very special settings for
slaves, that are not a good idea for MONITOR clients that are instead
normal clients even if they are conceptually slave-alike (since it is a
push protocol).
The backward-compatibility breakage resulting from "2" is considered to
be minimal to care, since MONITOR is a debugging command, and because
anyway this change is not going to break the format or the behavior, but
just when a connection is closed on big output buffer issues.
Lua scripts are executed in the context of the currently selected
database (as selected by the caller of the script).
However Lua scripts are also free to use the SELECT command in order to
affect other DBs. When SELECT is called frm Lua, the old behavior, before
this commit, was to automatically set the Lua caller selected DB to the
last DB selected by Lua. See for example the following sequence of
commands:
SELECT 0
SET x 10
EVAL "redis.call('select','1')" 0
SET x 20
Before this commit after the execution of this sequence of commands,
we'll have x=10 in DB 0, and x=20 in DB 1.
Because of the problem above, there was a bug affecting replication of
Lua scripts, because of the actual implementation of replication. It was
possible to fix the implementation of Lua scripts in order to fix the
issue, but looking closely, the bug is the consequence of the behavior
of Lua ability to set the caller's DB.
Under the old semantics, a script selecting a different DB, has no simple
ways to restore the state and select back the previously selected DB.
Moreover the script auhtor must remember that the restore is needed,
otherwise the new commands executed by the caller, will be executed in
the context of a different DB.
So this commit fixes both the replication issue, and this hard-to-use
semantics, by removing the ability of Lua, after the script execution,
to force the caller to switch to the DB selected by the Lua script.
The new behavior of the previous sequence of commadns is to just set
X=20 in DB 0. However Lua scripts are still capable of writing / reading
from different DBs if needed.
WARNING: This is a semantical change that will break programs that are
conceived to select the client selected DB via Lua scripts.
This fixes issue #1811.
It is more straightforward to just test for a numerical type avoiding
Lua's automatic conversion. The code is technically more correct now,
however Lua should automatically convert to number only if the original
type is a string that "looks like a number", and not from other types,
so practically speaking the fix is identical AFAIK.
The new check-for-number behavior of Lua arguments broke
users who use large strings of just integers.
The Lua number check would convert the string to a number, but
that breaks user data because
Lua numbers have limited precision compared to an arbitrarily
precise number wrapped in a string.
Regression fixed and new test added.
Fixes#1118 again.
The new ROLE command is designed in order to provide a client with
informations about the replication in a fast and easy to use way
compared to the INFO command where the same information is also
available.
Since there are ways to alter the configEpoch outside of the failover
procedure (for exampel CLUSTER SET-CONFIG-EPOCH and via the configEpoch
collision resolution algorithm), make always sure, before replacing our
configEpoch with a new one, that it is greater than the current one.
SET-CONFIG-EPOCH, used by redis-trib at cluster creation time, failed to
update the currentEpoch, making it possible after a failover for a
server to set its configEpoch to a value smaller than the current one
(since configEpochs are obtained using currentEpoch).
The bug totally break the Redis Cluster algorithms and protocols
allowing for permanent split brain conditions about the slots
configuration as shown in issue #1799.
I'm not sure if while the visibility is the inner block, the fact we
point to 'dbuf' is a problem or not, probably the stack var isx
guaranteed to live until the function returns. However obvious code is
better anyway.
The lua_to*string() family of functions use a non optimal format
specifier when converting integers to strings. This has both the problem
of the number being converted in exponential notation, which we don't
use as a Redis return value when floating point numbers are involed,
and, moreover, there is a loss of precision since the default format
specifier is not able to represent numbers that must be represented
exactly in the IEEE 754 number mantissa.
The new code handles it as a special case using a saner conversion.
This fixes issue #1118.
If we are in the signal handler, we don't want to handle
the signal again. In extreme cases, this can cause a stack overflow
and segfault Redis.
Fixes#1771
There is a time defined by REDIS_CLUSTER_WRITABLE_DELAY where fail -> ok
switch is not possible after startup as a master for some time, however
the contrary (ok -> fail) should always be possible.
Every log contains, just after the pid, a single character that provides
information about the role of an instance:
S - Slave
M - Master
C - Writing child
X - Sentinel
Behrad Zari discovered [1] and Josiah reported [2]: if you block
and wait for a list to exist, but the list creates from
a non-push command, the blocked client never gets notified.
This commit adds notification of blocked clients into
the DB layer and away from individual commands.
Lists can be created by [LR]PUSH, SORT..STORE, RENAME, MOVE,
and RESTORE. Previously, blocked client notifications were
only triggered by [LR]PUSH. Your client would never get
notified if a list were created by SORT..STORE or RENAME or
a RESTORE, etc.
Blocked client notification now happens in one unified place:
- dbAdd() triggers notification when adding a list to the DB
Two new tests are added that fail prior to this commit.
All test pass.
Fixes#1668
[1]: https://groups.google.com/forum/#!topic/redis-db/k4oWfMkN1NU
[2]: #1668
When scanning the argument list inside of a redis.call() invocation
for pre-cached values, there was no check being done that the
argument we were on was in fact within the bounds of the cache size.
So if a redis.call() command was ever executed with more than 32
arguments (current cache size #define setting) redis-server could
segfault.
Thanks to this change, when there is some code like:
clusterDoBeforeSleep(CLUSTER_TODO_UPDATE_STATE|...);
... and later before returning to the event loop ...
clusterUpdateState();
The clusterUpdateState() function will clar the flag and will not be
repeated in the clusterBeforeSleep() function. This especially important
for config save/fsync flags which are slow to execute and not a good
idea to repeat without a good reason.
This is implemented for all the CLUSTER_TODO flags.
The new command is able to reset a cluster node so that it starts again
as a fresh node. By default the command performs a soft reset (the same
as calling it as CLUSTER RESET SOFT), and the following steps are
performed:
1) All slots are set as unassigned.
2) The list of known nodes is flushed.
3) Node is set as master if it is a slave.
When an hard reset is performed with CLUSTER RESET HARD the following
additional operations are performed:
4) A new Node ID is created at random.
5) Epochs are set to 0.
CLUSTER RESET is useful both when the sysadmin wants to reconfigure a
node with a different role (for example turning a slave into a master)
and for testing purposes.
It also may play a role in automatically provisioned Redis Clusters,
since it allows to reset a node back to the initial state in order to be
reconfigured.
The previous code handling a lost slot (by another master with an higher
configuration for the slot) was defensive, considering it an error and
putting the cluster in an odd state requiring redis-cli fix.
This was changed, because actually this only happens either in a
legitimate way, with failovers, or when the admin messed with the config
in order to reconfigure the cluster. So the new code instead will try to
make sure that the keys stored match the new slots map, by removing all
the keys in the slots we lost ownership from.
The function that deletes the keys from the lost slots is called only
if the node does not lose all its slots (resulting in a reconfiguration
as a slave of the node that got ownership). This is an optimization
since the replication code will anyway flush all the instance data in
a faster way.
Using CLUSTER FAILOVER FORCE it is now possible to failover a master in
a forced way, which means:
1) No check to understand if the master is up is performed.
2) No data age of the slave is checked. Evan a slave with very old data
can manually failover a master in this way.
3) No chat with the master is attempted to reach its replication offset:
the master can just be down.
Automatic failovers only happen in Redis Cluster if the slave trying to
be elected was disconnected from its master for no more than 10 times
the node-timeout value. However there should be no such a check for
manual failovers, since these are initiated by the sysadmin that, in
theory, knows what she is doing when a slave is selected to be promoted.
Will be configurable / adaptive at some point but let's start with a
saner value compared to 1 sec which is not a good idea for big data
structures stored into a single key.
The error when the target key is busy was a generic one, while it makes
sense to be able to distinguish between the target key busy error and
the others easily.
The same change was operated for normal client connections. This is
important for Cluster as well, since when a node rejoins the cluster,
when a partition heals or after a restart, it gets flooded with new
connection attempts by all the other nodes trying to form a full
mesh again.
When a Sentinel performs a failover (successful or not), or when a
Sentinel votes for a different Sentinel trying to start a failover, it
sets a min delay before it will try to get elected for a failover.
While not strictly needed, because if multiple Sentinels will try
to failover the same master at the same time, only one configuration
will eventually win, this serialization is practically very useful.
Normal failovers are cleaner: one Sentinel starts to failover, the
others update their config when the Sentinel performing the failover
is able to get the selected slave to move from the role of slave to the
one of master.
However currently this timeout was implicit, so users could see
Sentinels not reacting, after a failed failover, for some time, without
giving any feedback in the logs to the poor sysadmin waiting for clues.
This commit makes Sentinels more verbose about the delay: when a master
is down and a failover attempt is not performed because the delay has
still not elaped, something like that will be logged:
Next failover delay: I will not start a failover
before Thu May 8 16:48:59 2014
Reusing small objects when possible is a major speedup under certain
conditions, since it is able to avoid the malloc/free pattern that
otherwise is performed for every argument in the client command vector.
Replace the three calls to Lua API lua_tostring, lua_lua_strlen,
and lua_isstring, with a single call to lua_tolstring.
~ 5% consistent speed gain measured.
Calling lua_gc() after every script execution is too expensive, and
apparently does not make the execution smoother: the same peak latency
was measured before and after the commit.
This change accounts for scripts execution speedup in the order of 10%.
The function showed up consuming a non trivial amount of time in the
profiler output. After this change benchmarking gives a 6% speed
improvement that can be consistently measured.
When the reply is only contained in the client static output buffer, use
a fast path avoiding the dynamic allocation of an SDS string to
concatenate the client reply objects.
Initially Redis Cluster accepted that after cluster creation all the
nodes were at configEpoch 0, evolving from zero as failovers happen.
However later the semantic was made more strict in order to make sure a
cluster has always all the master nodes with a different configEpoch,
which is more robust in some corner case (especially resulting from
errors by the system administrator).
To assign different configEpochs to different nodes at startup was a
task performed naturally by the config conflicts resolution algorithm
(see the Cluster specification). However this works well only for small
clusters or when there are actually just a few collisions, since it is
designed for exceptional cases.
When a large cluster is created hundred of nodes can be at epoch 0, so
the conflict resolution code is slow to provide an unique config to each
node. For this reason this new command was introduced. It can be called
only when a node is totally fresh: no other nodes known, and configEpoch
set to zero, so it is safe even against misuses.
redis-trib will use the new command in order to start the cluster
already setting an incremental unique config to every node.
This commit adds peer ID caching in the client structure plus an API
change and the use of sdsMakeRoomFor() in order to improve the
reallocation pattern to generate the CLIENT LIST output.
Both the changes account for a very significant speedup.
This commit also fixes a bug in the implementation of sdscatfmt()
resulting from stale references to the SDS string header after
sdsMakeRoomFor() calls.
sdscatprintf() relies on printf() family libc functions and is sometimes
too slow in critical code paths. sdscatfmt() is an alternative which is:
1) Far less capable.
2) Format specifier uncompatible.
3) Faster.
It is suitable to be used in those speed critical code paths such as
CLIENT LIST output generation.
When we are blocked and a few events a processed from time to time, it
is smarter to call the event handler a few times in order to handle the
accept, read, write, close cycle of a client in a single pass, otherwise
there is too much latency added for clients to receive a reply while the
server is busy in some way (for example during the DB loading).
When the listening sockets readable event is fired, we have the chance
to accept multiple clients instead of accepting a single one. This makes
Redis more responsive when there is a mass-connect event (for example
after the server startup), and in workloads where a connect-disconnect
pattern is used often, so that multiple clients are waiting to be
accepted continuously.
As a side effect, this commit makes the LOADING, BUSY, and similar
errors much faster to deliver to the client, making Redis more
responsive when there is to return errors to inform the clients that the
server is blocked in an not interruptible operation.
We should return REDIS_ERR to signal we can't read the configuration
because there is no config file only after checking errno, othewise
we risk to rewrite an existing file that was not accessible for some
other reason.
This was a common source of problems among users.
The solution adopted is not bullet-proof as if the user deletes the
nodes.conf file manually, and starts a new instance with the same
nodes.conf file path, two instances will use the same file. However
following this reasoning the user may drop a nuclear bomb into the
datacenter as well.
I happen to be working on a system that lacks urandom. While the code does try
to handle this case and artificially create some bytes if the file pointer is
empty, it does try to close it unconditionally, leading to a segfault.
When we set a protocol error we should return with REDIS_ERR to let the
caller know it should stop processing the client.
Bug found in a code auditing related to issue #1699.
The internal HLL raw encoding used by PFCOUNT when merging multiple keys
is aligned to 8 bits (1 byte per register) so we can exploit this to
improve performances by processing multiple bytes per iteration.
In benchmarks the new code was several times faster with HLLs with many
registers set to zero, while no slowdown was observed with populated
HLLs.
When the register is set to zero, we need to add 2^-0 to E, which is 1,
but it is faster to just add 'ez' at the end, which is the number of
registers set to zero, a value we need to compute anyway.
Given that the code was written with a 2 years pause... something
strange happened in the middle. So there was no function to free a
lex range min/max objects, and in some places the range was passed by
value.
After running a few benchmarks, 3000 looks like a reasonable value to
keep HLLs with a few thousand elements small while the CPU cost is
still not huge.
This covers all the cases where the dense representation would use N
orders of magnitude more space, like in the case of many HLLs with
carinality of a few tens or hundreds.
It is not impossible that in the future this gets user configurable,
however it is easy to pick an unreasoable value just looking at savings
in the space dimension without checking what happens in the time
dimension.
Bulk length for registers was emitted too early, so if there was a bug
the reply looked like a long array with just one element, blocking the
client as result.
The function checks if all the HLL_REGISTERS were processed during the
convertion from sparse to dense encoding, returning REDIS_OK or
REDIS_ERR to signal a corruption problem.
A bug in PFDEBUG GETREG was fixed: when the object is converted to the
dense representation we need to reassign the new pointer to the header
structure pointer.
Provides a human readable description of the opcodes composing a
run-length encoded HLL (sparse encoding).
The command is only useful for debugging / development tasks.
The new API takes directly the object doing everything needed to
turn it into a dense representation, including setting the new
representation as object->ptr.
Code never tested, but the basic layout is shaped in this commit.
Also missing:
1) Sparse -> Dense conversion function.
2) New HLL object creation using the sparse representation.
3) Implementation of PFMERGE for the sparse representation.
Metadata are now placed at the start of the representation as an header.
There is a proper structure to access the representation.
Still work to do in order to truly abstract the implementation from the
representation, commands still work assuming dense representation.
After running a few simulations with different alternative encodings,
it was found that the VAL opcode performs better using 5 bits for the
value and 2 bits for the run length, at least for cardinalities in the
range of interest.
adjustOpenFilesLimit() and clusterUpdateSlotsWithConfig() that were
assuming uint64_t is the same as unsigned long long, which is true
probably for all the systems out there that we target, but still GCC
emitted a warning since technically they are two different types.
This will be a non-op most of the times since the object will be
unshared / decoded, however it is more technically correct to start this
way since the object may be decoded even in the read-only code path.
Using a seed of zero has the side effect of having the empty string
hashing to what is a very special case in the context of HyperLogLog: a
very long run of zeroes.
This did not influenced the correctness of the result with 16k registers
because of the harmonic mean, but still it is inconvenient that a so
obvious value maps to a so special hash.
The seed 0xadc83b19 is used instead, which is the first 64 bits of the
SHA1 of the empty string.
Reference: issue #1657.
We need to guarantee that the last bit is 1, otherwise an element may
hash to just zeroes with probability 1/(2^64) and trigger an infinite
loop.
See issue #1657.
This will allow future changes like compressed representations.
Currently the magic is not checked for performance reasons but this may
change in the future, for example if we add new types encoded in strings
that may have the same size of HyperLogLogs.
Better results can be achieved by compensating for the bias of the raw
approximation just after 2.5m (when LINEARCOUNTING is no longer used) by
using a polynomial that approximates the bias at a given cardinality.
The curve used was found using this web page:
http://www.xuru.org/rt/PR.asp
That performs polynomial regression given a set of values.
The following form is given:
HLLADD myhll
No element is provided in the above case so if 'myhll' var does not
exist the result is to just create an empty HLL structure, and no update
will be performed on the registers.
In this case, the DB should still be set dirty and the command
propagated.
The HyperLogLog original paper suggests using LINEARCOUNTING for
cardinalities < 2.5m, however for P=14 the median / max error
curves show that a value of '3' is the best pick for m = 16384.
The more we add elements to an HyperLogLog counter, the smaller is
the probability that we actually update some register.
From this observation it is easy to see how it is possible to use
caching of a previously computed cardinality and reuse it to serve
HLLCOUNT queries as long as no register was updated in the data
structure.
This commit does exactly this by using just additional 8 bytes for the
data structure to store a 64 bit unsigned integer value cached
cardinality. When the most significant bit of the 64 bit integer is set,
it means that the value computed is no longer usable since at least a
single register was modified and we need to recompute it at the next
call of HLLCOUNT.
The value is always stored in little endian format regardless of the
actual CPU endianess.
All the Redis functions that need to modify the string value of a key in
a destructive way (APPEND, SETBIT, SETRANGE, ...) require to make the
object unshared (if refcount > 1) and encoded in raw format (if encoding
is not already REDIS_ENCODING_RAW).
This was cut & pasted many times in multiple places of the code. This
commit puts the small logic needed into a function called
dbUnshareStringValue().
We need to be sure that you can save a dataset in a Redis instance,
reload it in a different architecture, and continue to count in the same
HyperLogLog structure.
So 32 and 64 bit, little or bit endian, must all guarantee to output the
same hash for the same element.
The new representation is more obvious, starting from the LSB of the
first byte and using bits going to MSB, and passing to next byte as
needed.
There was also a subtle error: first two bits were unused, everything
was carried over on the right of two bits, even if it worked because of
the code requirement of always having a byte more at the end.
During the rewrite the code was made safer trying to avoid undefined
behavior due to shifting an uint8_t for more than 8 bits.
To test the bitfield array of counters set/get macros from the Redis Tcl
suite is hard, so a specialized command that is able to test the
internals was developed.
This is not really an error but something that always happens for
example when creating a new cluster, or if the sysadmin rejoins manually
a node that is already known.
Since useless logs don't help, moved to VERBOSE level.
New config epochs must always be obtained incrementing the currentEpoch,
that is itself guaranteed to be >= the max configEpoch currently known
to the node.
redis-trib used to allocate slots not considering fractions of nodes
when computing the slots_per_node amount. So the fractional part was
carried over till the end of the allocation, where the last node
received a few more slots than any other (or a lot more if the cluster
was composed of many nodes).
The computation was changed to allocate slots more evenly when they are
not exactly divisible for the number of masters we have.
The slave election in Redis Cluster guarantees that slaves promoted to
masters always end with unique config epochs, however failures during
manual reshardings, software bugs and operational errors may in theory
cause two nodes to have the same configEpoch.
This commit introduces a mechanism to eventually always end with different
configEpochs if a collision ever happens.
As a (wanted) side effect, this also ensures that after a new cluster
is created, all nodes will end with a different configEpoch automatically.
Bug found by the continuous integration test running the Redis
with valgrind:
==6245== Invalid read of size 8
==6245== at 0x4C2DEEF: memcpy@GLIBC_2.2.5 (mc_replace_strmem.c:876)
==6245== by 0x41F9E6: freeMemoryIfNeeded (redis.c:3010)
==6245== by 0x41D2CC: processCommand (redis.c:2069)
memmove() size argument was accounting for an extra element, going
outside the bounds of the array.
In this commit:
* Decrement steps are semantically differentiated from the reserved FDs.
Previously both values were 32 but the meaning was different.
* Make it clear that we save setrlimit errno.
* Don't explicitly handle wrapping of 'f', but prevent it from
happening.
* Add comments to make the function flow more readable.
This integrates PR #1630
In sentinelFlushConfig() fd could be undefined when the following if
statement was true:
if (rewrite_status == -1) goto werr;
This could cause random file descriptors to get closed.
Previously, the (!fp) would only catch lack of free space
under OS X. Linux waits to discover it can't write until
it actually writes contents to disk.
(fwrite() returns success even if the underlying file
has no free space to write into. All the errors
only show up at flush/sync/close time.)
Fixesantirez/redis#1604
Also update the original REDIS_EVENTLOOP_FDSET_INCR to
include REDIS_MIN_RESERVED_FDS. REDIS_EVENTLOOP_FDSET_INCR
exists to make sure more than (maxclients+RESERVED) entries
are allocated, but we can only guarantee that if we include
the current value of REDIS_MIN_RESERVED_FDS as a minimum
for the INCR size.
This got removed in 2e5c394 during a new feature addition.
The prior commit had "break if masters.length == masters_count"
but we are guaranteed to aready have that condition met since
otherwise we would haven't gotten this far.
Without this break statement, it's possible some masters may
be forgotten and have zero replicas while other masters have
more than their requested number of replicas.
Thanks to carlos for pointing out this regression at:
https://groups.google.com/forum/#!topic/redis-db/_WVVqDw5B7c
This bug was introduced in 2e5c394f during a refactor.
It took me a while to understand what was going on with
the code, so I've refactored it further by:
- Replacing boolean values with meaningful symbols
- Replacing 'i' with a meaningful variable name
- Adding the proper abort check
- Factoring out now duplicated conditionals
- Adding optional verbose logging (we're inside *four*
different looping constructs, so it takes a while to
figure out where all the moving parts are)
- Updating comment for the section
This fixes a problem when the number of master instances
equaled the number of replica instances. Before, when
there were equal numbers of both, nodes_count would go to
zero, but the while loop would spin in i < @replicas because
i would never be updated (because the nodes_list of each ip
was length == 0, which triggered an endless loop of
next -> i = 0 -> 0 < 1? -> true -> next -> i = 0 ...)
Thanks to carlo who found this problem at:
https://groups.google.com/forum/#!topic/redis-db/_WVVqDw5B7c
Fun fact: rlim_t is an unsigned long long on all platforms.
Continually subtracting from a rlim_t makes it get smaller
and smaller until it wraps, then you're up to 2^64-1.
This was causing an infinite loop on Redis startup if
your ulimit was extremely (almost comically) low.
The case of (f > oldlimit) would never be met in a case like:
f = 150
while (f > 20) f -= 128
Since f is unsigned, it can't go negative and would
take on values of:
Iteration 1: 150 - 128 => 22
Iteration 2: 22 - 128 => 18446744073709551510
Iterations 3-∞: ...
To catch the wraparound, we use the previous value of f
stored in limit.rlimit_cur. If we subtract from f and
get a larger number than the value it had previously,
we print an error and exit since we don't have enough
file descriptors to help the user at this point.
Thanks to @bs3g for the inspiration to fix this problem.
Patches existed from @bs3g at antirez#1227, but I needed to repair a few other
parts of Redis simultaneously, so I didn't get a chance to use them.
The log messages about open file limits have always
been slightly opaque and confusing. Here's an attempt to
fix their wording, detail, and meaning. Users will have a
better understanding of how to fix very common problems
with these reworded messages.
Also, we handle a new error case when maxclients becomes less
than one, essentially rendering the server unusable. We
now exit on startup instead of leaving the user with a server
unable to handle any connections.
This fixes antirez#356 as well.
32 was the additional number of file descriptors Redis
would reserve when managing a too-low ulimit. The
number 32 was in too many places statically, so now
we use a macro instead that looks more appropriate.
When Redis sets up the server event loop, it uses:
server.maxclients+REDIS_EVENTLOOP_FDSET_INCR
So, when reserving file descriptors, it makes sense to
reserve at least REDIS_EVENTLOOP_FDSET_INCR FDs instead
of only 32. Currently, REDIS_EVENTLOOP_FDSET_INCR is
set to 128 in redis.h.
Also, I replaced the static 128 in the while f < old loop
with REDIS_EVENTLOOP_FDSET_INCR as well, which results
in no change since it was already 128.
Impact: Users now need at least maxclients+128 as
their open file limit instead of maxclients+32 to obtain
actual "maxclients" number of clients. Redis will carve
the extra REDIS_EVENTLOOP_FDSET_INCR file descriptors it
needs out of the "maxclients" range instead of failing
to start (unless the local ulimit -n is too low to accomidate
the request).
Everywhere in the Redis code base, maxclients is treated
as an int with (int)maxclients or `maxclients = atoi(source)`,
so let's make maxclients an int.
This fixes a bug where someone could specify a negative maxclients
on startup and it would work (as well as set maxclients very high)
because:
unsigned int maxclients;
char *update = "-300";
maxclients = atoi(update);
if (maxclients < 1) goto fail;
But, (maxclients < 1) can only catch the case when maxclients
is exactly 0. maxclients happily sets itself to -300, which isn't
-300, but rather 4294966996, which isn't < 1, so... everything
"worked."
maxclients config parsing checks for the case of < 1, but maxclients
CONFIG SET parsing was checking for case of < 0 (allowing
maxclients to be set to 0). CONFIG SET parsing is now updated to
match config parsing of < 1.
It's tempting to add a MINIMUM_CLIENTS define, but... I didn't.
These changes were inspired by antirez#356, but this doesn't
fix that issue.
Obtaining the RSS (Resident Set Size) info is slow in Linux and OSX.
This slowed down the generation of the INFO 'memory' section.
Since the RSS does not require to be a real-time measurement, we
now sample it with server.hz frequency (10 times per second by default)
and use this value both to show the INFO rss field and to compute the
fragmentation ratio.
Practically this does not make any difference for memory profiling of
Redis but speeds up the INFO call significantly.
For small content the function now tries to use a static buffer to avoid
a malloc/free cycle that is too costly when the function is used in the
context of performance critical code path such as INFO output generation.
This change was verified to have positive effects in the execution speed
of the INFO command.
Uname was profiled to be a slow syscall. It produces always the same
output in the context of a single execution of Redis, so calling it at
every INFO output generation does not make too much sense.
The uname utsname structure was modified as a static variable. At the
same time a static integer was added to check if we need to call uname
the first time.
sdscatvprintf() uses a loop where it tries to output the formatted
string in a buffer of the initial length, if there was not enough room,
a buffer of doubled size is tried and so forth.
The initial guess for the buffer length was very poor, an hardcoded
"16". This caused the printf to be processed multiple times without a
good reason. Given that printf functions are already not fast, the
overhead was significant.
The new heuristic is to use a buffer 4 times the length of the format
buffer, and 32 as minimal size. This appears to be a good balance for
typical uses of the function inside the Redis code base.
This change improved INFO command performances 3 times.
This is safer as by default maxmemory should just set a memory limit
without any key to be deleted, unless the policy is set to something
more relaxed.
There were 2 spare bits inside the Redis object structure that are now
used in order to enlarge 4x the range of the LRU field.
At the same time the resolution was improved from 10 to 1 second: this
still provides 194 days before the LRU counter overflows (restarting from
zero).
This is not a problem since it only causes lack of eviction precision for
objects not touched for a very long time, and the lack of precision is
only temporary.
This new function is useful to get a number of random entries from an
hash table when we just need to do some sampling without particularly
good distribution.
It just jumps at a random place of the hash table and returns the first
N items encountered by scanning linearly.
The main usefulness of this function is to speedup Redis internal
sampling of the key space, for example for key eviction or expiry.
This is an improvement over the previous eviction algorithm where we use
an eviction pool that is persistent across evictions of keys, and gets
populated with the best candidates for evictions found so far.
It allows to approximate LRU eviction at a given number of samples
better than the previous algorithm used.
For testing purposes it is handy to have a very high resolution of the
LRU clock, so that it is possible to experiment with scripts running in
just a few seconds how the eviction algorithms works.
This commit allows Redis to use the cached LRU clock, or a value
computed on demand, depending on the resolution. So normally we have the
good performance of a precomputed value, and a clock that wraps in many
days using the normal resolution, but if needed, changing a define will
switch behavior to an high resolution LRU clock.
GCC-4.9 warned about this, but clang didn't.
This commit fixes warning:
sentinel.c: In function 'sentinelReceiveHelloMessages':
sentinel.c:2156:43: warning: variable 'master' set but not used [-Wunused-but-set-variable]
sentinelRedisInstance *ri = c->data, *master;
Test sentinel.tilt condition on top and return if it is true.
This allows to remove the check for the tilt condition in the remaining
code paths of the function.
Failure detection in Sentinel is ping-pong based. It used to work by
remembering the last time a valid PONG reply was received, and checking
if the reception time was too old compared to the current current time.
PINGs were sent at a fixed interval of 1 second.
This works in a decent way, but does not scale well when we want to set
very small values of "down-after-milliseconds" (this is the node
timeout basically).
This commit reiplements the failure detection making a number of
changes. Some changes are inspired to Redis Cluster failure detection
code:
* A new last_ping_time field is added in representation of instances.
If non zero, we have an active ping that was sent at the specified
time. When a valid reply to ping is received, the field is zeroed
again.
* last_ping_time is not reset when we reconnect the link or send a new
ping, so from our point of view it represents the time we started
waiting for the instance to reply to our pings without receiving a
reply.
* last_ping_time is now used in order to check if the instance is
timed out. This means that we can have a node timeout of 100
milliseconds and yet the system will work well since the new check is
not bound to the period used to send pings.
* Pings are now sent every second, or often if the value of
down-after-milliseconds is less than one second. With a lower limit of
10 HZ ping frequency.
* Link reconnection code was improved. This is used in order to try to
reconnect the link when we are at 50% of the node timeout without a
valid reply received yet. However the old code triggered unnecessary
reconnections when the node timeout was very small. Now that should be
ok.
The new code passes the tests but more testing is needed and more unit
tests stressing the failure detector, so currently this is merged only
in the unstable branch.
Sentinel's main safety argument is that there are no two configurations
for the same master with the same version (configuration epoch).
For this to be true Sentinels require to be authorized by a majority.
Additionally Sentinels require to do two important things:
* Never vote again for the same epoch.
* Never exchange an old vote for a fresh one.
The first prerequisite, in a crash-recovery system model, requires to
persist the master->leader_epoch on durable storage before to reply to
messages. This was not the case.
We also make sure to persist the current epoch in order to never reply
to stale votes requests from other Sentinels, after a recovery.
The configuration is persisted by making use of fsync(), this is
considered in the context of this code a good enough guarantee that
after a restart our durable state is restored, however this may not
always be the case depending on the kind of hardware and operating
system used.
Now the way HELLO messages are received is unified.
Now it is no longer needed for Sentinels to converge to the higher
configuration for a master to be able to chat via some Redis instance,
the are able to directly exchanges configurations.
Note that this commit does not include the (trivial) change needed to
send HELLO messages to Sentinel instances as well, since for an error I
committed the change in the previous commit that refactored hello
messages processing into a separated function.
Example: if the user will try to configure a cluster with 9 nodes,
asking for 1 slave for master, redis-trib will configure a 4 masters
cluster with 1 slave each as usually, but this time will assign the
spare node as a slave of one of the masters.
By manually modifying nodes configurations in random ways, it is possible
to create the following scenario:
A is serving keys for slot 10
B is manually configured to serve keys for slot 10
A receives an update from B (or another node) where it is informed that
the slot 10 is now claimed by B with a greater configuration epoch,
however A still has keys from slot 10.
With this commit A will put the slot in error setting it in IMPORTING
state, so that redis-trib can detect the issue.
The new "error" subcommand of the DEBUG command can reply with an user
selected error, specified as its sole argument:
DEBUG ERROR "LOADING please wait..."
The error is generated just prefixing the command argument with a "-"
character, and replacing newlines with spaces (since error replies can't
include newlines).
The goal of the command is to help in Client libraries unit tests by
making simple to simulate a command call triggering a given error.
getKeysFromCommand() is designed to be called with the command arguments
passing the basic arity checks described in the command table.
DEBUG CMDKEYS must provide the same guarantees for calling
getKeysFromCommand() to be safe.
Examples:
redis 127.0.0.1:6379> debug cmdkeys set foo bar
1) "foo"
redis 127.0.0.1:6379> debug cmdkeys mget a b c
1) "a"
2) "b"
3) "c"
redis 127.0.0.1:6379> debug cmdkeys zunionstore foo 2 a b
1) "a"
2) "b"
3) "foo"
redis 127.0.0.1:6379> debug cmdkeys ping
(empty list or set)
There is the exception of a "constant" BY pattern that is used in order
to signal to don't sort at all. In this case no lookup is needed so it
is possible to support this case in Cluster mode.
Previously we used zunionInterGetKeys(), however after this function was
fixed to account for the destination key (not needed when the API was
designed for "diskstore") the two set of commands can no longer be served
by an unique keys-extraction function.
This API originated from the "diskstore" experiment, not for Redis
Cluster itself, so there were legacy/useless things trying to
differentiate between keys that are going to be overwritten and keys
that need to be fetched from disk (preloaded).
All useless with Cluster, so removed with the result of code
simplification.
The code was already correct but it was using that bindaddr[0] is set to
NULL as a side effect of current implementation if no bind address is
configured. This is not guarnteed to hold true in the future.
When node-timeout is too small, in the order of a few milliseconds,
there is no way the voting process can terminate during that time, so we
set a lower limit for the failover timeout of two seconds.
The retry time is set to two times the failover timeout time, so it is
at least 4 seconds.
The previous implementation wasn't taking into account
the storage key in position 1 being a requirement (it
was only counting the source keys in positions 3 to N).
Fixesantirez/redis#1581
This value needs to be set to zero (in addition to
stat_numcommands) or else people may see
a negative operations per second count after they
run CONFIG RESETSTAT.
Fixesantirez/redis#1577
The first address specified as a bind parameter
(server.bindaddr[0]) gets used as the source IP
for cluster communication.
If no bind address is specified by the user, the
behavior is unchanged.
This patch allows multiple Redis Cluster instances
to communicate when running on the same interface
of the same host.
Sentinel needs to avoid split brain conditions due to multiple sentinels
trying to get voted at the exact same time.
So far some desynchronization was provided by fluctuating server.hz,
that is the frequency of the timer function call. However the
desynchonization provided in this way was not enough when using many
Sentinel instances, especially when a large quorum value is used in
order to force a greater degree of agreement (more than N/2+1).
It was verified that it was likely to trigger a split brain
condition, forcing the system to try again after a timeout.
Usually the system will succeed after a few retries, but this is not
optimal.
This commit desynchronizes instances in a more effective way to make it
likely that the first attempt will be successful.
This is still code to rework in order to use agreement to obtain a new
configEpoch when a slot is migrated, however this commit handles the
special case that happens when the nodes are just started and everybody
has a configEpoch of 0. In this special condition to have the maximum
configEpoch is not enough as the special epoch 0 is not unique (all the
others are).
This does not fixes the intrinsic race condition of a failover happening
while we are resharding, that will be addressed later.
used_memory_peak only updates in serverCron every server.hz,
but Redis can use more memory and a user can request memory
INFO before used_memory_peak gets updated in the next
cron run.
This patch updates used_memory_peak to the current
memory usage if the current memory usage is higher
than the recorded used_memory_peak value.
(And it only calls zmalloc_used_memory() once instead of
twice as it was doing before.)
This commit reworks the redis-cli --bigkeys command to provide more
information about our progress as well as output summary information
when we're done.
- We now show an approximate percentage completion as we go
- Hiredis pipelining is used for TYPE and SIZE retreival
- A summary of keyspace distribution and overall breakout at the end
With the new behavior it is possible to specify just the start in the
range (the end will be assumed to be the first byte), or it is possible
to specify both start and end.
This is useful to change the behavior of the command when looking for
zeros inside a string.
1) If the user specifies both start and end, and no 0 is found inside
the range, the command returns -1.
2) If instead no range is specified, or just the start is given, even
if in the actual string no 0 bit is found, the command returns the
first bit on the right after the end of the string.
So for example if the string stored at key foo is "\xff\xff":
BITPOS foo (returns 16)
BITPOS foo 0 -1 (returns -1)
BITPOS foo 0 (returns 16)
The idea is that when no end is given the user is just looking for the
first bit that is zero and can be set to 1 with SETBIT, as it is
"available". Instead when a specific range is given, we just look for a
zero within the boundaries of the range.
This commit changes the findBigKeys() function in redis-cli.c to use the new
SCAN command for iterating the keyspace, rather than RANDOMKEY. Because we
can know when we're done using SCAN, it will exit after exhausting the keyspace.
The computation is just something to take the CPU busy, no need to use a
specific type. Since stdint.h was not included this prevented
compilation on certain systems.
Now that we have a runtime configuration system, it is very important to
be able to log how the Sentinel configuration changes over time because
of API calls.
This error was conceived for the older version of Sentinel that worked
via master redirection and that was not able to get configuration
updates from other Sentinels via the Pub/Sub channel of masters or
slaves.
This reply does not make sense today, every Sentinel should reply with
the best information it has currently. The error will make even more
sense in the future since the plan is to allow Sentinels to update the
configuration of other Sentinels via gossip with a direct chat without
the prerequisite that they have at least a monitored instance in common.
If you launch redis with `redis-server --sentinel` then
in a ps, your output only says "redis-server IP:Port" — this
patch changes the proc title to include [sentinel] or
[cluster] depending on the current server mode:
e.g. "redis-server IP:Port [sentinel]"
"redis-server IP:Port [cluster]"
The default cluster control port is 10,000 ports higher than
the base Redis port. If Redis is started on a too-high port,
Cluster can't start and everything will exit later anyway.
Report the actual port used for the listening attempt instead of
server.port.
Originally, Redis would just listen on server.port.
But, with clustering, Redis uses a Cluster Port too,
so we can't say server.port is always where we are listening.
If you tried to launch Redis with a too-high port number (any
port where Port+10000 > 65535), Redis would refuse to start, but
only print an error saying it can't connect to the Redis port.
This patch fixes much confusions.
If we can't reconfigure a slave in time during failover, go forward as
anyway the slave will be fixed by Sentinels in the future, once they
detect it is misconfigured.
Otherwise a failover in progress may never terminate if for some reason
the slave is uncapable to sync with the master while at the same time
it is not disconnected.
The code tried to obtain the configuration file absolute path after
processing the configuration file. However if config file was a relative
path and a "dir" statement was processed reading the config, the absolute
path obtained was wrong.
With this fix the absolute path is obtained before processing the
configuration while the server is still in the original directory where
it was executed.
Now it logs the file name if it is not accessible. Also there is a
different error for the missing config file case, and for the non
writable file case.
server.unixtime and server.mstime are cached less precise timestamps
that we use every time we don't need an accurate time representation and
a syscall would be too slow for the number of calls we require.
Such an example is the initialization and update process of the last
interaction time with the client, that is used for timeouts.
However rdbLoad() can take some time to load the DB, but at the same
time it did not updated the time during DB loading. This resulted in the
bug described in issue #1535, where in the replication process the slave
loads the DB, creates the redisClient representation of its master, but
the timestamp is so old that the master, under certain conditions, is
sensed as already "timed out".
Thanks to @yoav-steinberg and Redis Labs Inc for the bug report and
analysis.
This commit fixes a serious Lua scripting replication issue, described
by Github issue #1549. The root cause of the problem is that scripts
were put inside the script cache, assuming that slaves and AOF already
contained it, even if the scripts sometimes produced no changes in the
data set, and were not actaully propagated to AOF/slaves.
Example:
eval "if tonumber(KEYS[1]) > 0 then redis.call('incr', 'x') end" 1 0
Then:
evalsha <sha1 step 1 script> 1 0
At this step sha1 of the script is added to the replication script cache
(the script is marked as known to the slaves) and EVALSHA command is
transformed to EVAL. However it is not dirty (there is no changes to db),
so it is not propagated to the slaves. Then the script is called again:
evalsha <sha1 step 1 script> 1 1
At this step master checks that the script already exists in the
replication script cache and doesn't transform it to EVAL command. It is
dirty and propagated to the slaves, but they fail to evaluate the script
as they don't have it in the script cache.
The fix is trivial and just uses the new API to force the propagation of
the executed command regardless of the dirty state of the data set.
Thank you to @minus-infinity on Github for finding the issue,
understanding the root cause, and fixing it.
A system similar to the RDB write error handling is used, in which when
we can't write to the AOF file, writes are no longer accepted until we
are able to write again.
For fsync == always we still abort on errors since there is currently no
easy way to avoid replying with success to the user otherwise, and this
would violate the contract with the user of only acknowledging data
already secured on disk.
Avoid to trash a configEpoch for every slot migrated if this node has
already the max configEpoch across the cluster.
Still work to do in this area but this avoids both ending with a very
high configEpoch without any reason and to flood the system with fsyncs.
The actual goal of the function was to get the max configEpoch found in
the cluster, so make it general by removing the assignment of the max
epoch to currentEpoch that is useful only at startup.
Removed a stale conditional preventing the configEpoch from incrementing
after the import in certain conditions. Since the master got a new slot
it should always claim a new configuration.
The node receiving the hash slot needs to have a version that wins over
the other versions in order to force the ownership of the slot.
However the current code is far from perfect since a failover can happen
during the manual resharding. The fix is a work in progress but the
bottom line is that the new version must either be voted as usually,
set by redis-trib manually after it makes sure can't be used by other
nodes, or reserved configEpochs could be used for manual operations (for
example odd versions could be never used by slaves and are always used
by CLUSTER SETSLOT NODE).
During slots migration redis-trib can send a number of SETSLOT commands.
Fsyncing every time is a bit too much in production as verified
empirically.
To make sure configs are fsynced on all nodes after a resharding
redis-trib may send something like CLUSTER CONFSYNC.
In this case fsyncs were not providing too much value since anyway
processes can crash in the middle of the resharding of an hash slot, and
redis-trib should be able to recover from this condition anyway.
If the slot is manually assigned to another node, clear the migrating
status regardless of the fact it was previously assigned to us or not,
as long as we no longer have keys for this slot.
This avoid a race during slots migration that may leave the slot in
migrating status in the source node, since it received an update message
from the destination node that is already claiming the slot.
This way we are sure that redis-trib at the end of the slot migration is
always able to close the slot correctly.
If someone asks for SYNC or PSYNC from redis-cli,
automatically enter slaveMode (as if they ran
redis-cli --slave) and continue printing the replication
stream until either they Ctrl-C or the master gets disconnected.
Currently this is marginally useful, only to make sure two keys are in
the same hash slot when the cluster is stable (no rehashing in
progress).
In the future it is possible that support will be added to run
mutli-keys operations with keys in the same hash slot.
Sometime an osx master with a Linux server over a slow link caused
a strange error where osx called the writable function for
the socket but actually apparently there was no room in the socket
buffer to accept the write: write(2) call returned an EAGAIN error,
that was not checked, so we considered write(2) == 0 always as a connection
reset, which was unfortunate since the bulk transfer has to start again.
Also more errors are logged with the WARNING level in the same code path
now.
When a slave requests masters vote for a manual failover, the
REQUEST_AUTH message is flagged in a special way in order to force the
masters to give the authorization even if the master is not marked as
failing.
The API is one of the bulding blocks of CLUSTER FAILOVER command that
executes a manual failover in Redis Cluster. However exposed as a
command that the user can call directly, it makes much simpler to
upgrade a standalone Redis instance using a slave in a safer way.
The commands works like that:
CLIENT PAUSE <milliesconds>
All the clients that are not slaves and not in MONITOR state are paused
for the specified number of milliesconds. This means that slaves are
normally served in the meantime.
At the end of the specified amount of time all the clients are unblocked
and will continue operations normally. This command has no effects on
the population of the slow log, since clients are not blocked in the
middle of operations but only when there is to process new data.
Note that while the clients are unblocked, still new commands are
accepted and queued in the client buffer, so clients will likely not
block while writing to the server while the pause is active.
Keys expiring in the middle of the execution of Lua scripts are to
create inconsistencies in masters and / or AOF files. See the following
example:
if redis.call("exists",KEYS[1]) == 1
then
redis.call("incr","mycounter")
end
if redis.call("exists",KEYS[1]) == 1
then
return redis.call("incr","mycounter")
end
The script executes two times the same *if key exists then incrementcounter*
logic. However the two executions will work differently in the master and
the slaves, provided some unlucky timing happens.
In the master the first time the key may still exist, while the second time
the key may no longer exist. This will result in the key incremented just one
time. However as a side effect the master will generate a synthetic
`DEL` command in the replication channel in order to force the slaves to
expire the key (given that key expiration is master-driven).
When the same script will run in the slave, the key will no longer be
there, so the script will not increment the key.
The key idea used to implement the expire-at-first-lookup semantics was
provided by Marc Gravell.
server.lua_time_start is expressed in milliseconds. Use mstime_t instead
of long long, and populate it with mstime() instead of ustime()/1000.
Functionally identical but more natural.
In high RPS environments, the default listen backlog is not sufficient, so
giving users the power to configure it is the right approach, especially
since it requires only minor modifications to the code.
The check was placed in a way that conflicted with the continue
statements used by the node hearth beat code later that needs to skip
the current node sometimes. Moved at the start of the function so that's
always executed.
This feature allows slaves to migrate to orphaned masters (masters
without working slaves), as long as a set of conditions are met,
including the fact that the migrating slave needs to be in a
master-slaves ring with at least another slave working.
When we schedule a failover, broadcast a PONG to the slaves.
The other slaves that plan to get elected will do the same too, this way
it is likely that every slave will have a good picture of its own rank.
Note that this is N*N messages where N is the number of slaves for the
failing master, however usually even large clusters have many master
nodes but a limited number of replicas per node, so this is harmless.
Note that when we compute the initial delay, there are probably still
more up to date information to receive from slaves with new offsets, so
the delay is recomputed when new data is available.
Return the number of slaves for the same master having a better
replication offset of the current slave, that is, the slave "rank" used
to pick a delay before the request for election.
Accessing to the 'myself' node, the node representing the currently
running instance, is handy without the need to type
server.cluster->myself every time.
The two fields are used in order to remember the latest known
replication offset and the time we received it from other slave nodes.
This will be used by slaves in order to start the election procedure
with a delay that is proportional to the rank of the slave among the
other slaves for this master, when sorted for replication offset.
Usually this allows the slave with the most updated offset to win the
election and replace the failing master in the cluster.
Incremental flushing in rio.c is only used to avoid huge kernel buffers
synched to slow disks creating big latency spikes, so this fix has no
durability implications, however it is certainly more correct to make
sure that the FILE buffers are flushed to the kernel before calling
fsync on the file descriptor.
Thanks to Li Shao Kai for reporting this issue in the Redis mailing
list.
One of the simple heuristics used by Redis Cluster in order to avoid
losing data in the typical failure modes created by the asynchronous
replication with the slaves (a master is unable, when accepting a
write, to immediately tell if it should be really accepted or refused
because of a configuration change), is to wait some time before to
rejoin the cluster after being partitioned away from the majority of
instances.
A similar condition happens when a master is restarted. It does not know
if it was already failed over, nor if all the clients have already an
updated configuration about the cluster map, so it is possible that
clients will try to write to stale masters that were restarted.
In a similar way this commit changes masters behavior so they wait
2000 milliseconds before accepting writes after a reboot. There is
nothing special about 2 seconds if not to be a value supposedly larger
a few orders of magnitude compared to the cluster bus communication
latencies.
The code was doing checks for slaves that should be done only when the
instance is currently a master. Switching a slave from a master to
another one should just work.
When an instance is potentially set to replicate with another master, it
is conceptually disconnected forever, since we have no old copy of the
dataset for this master in memory.
CLUSTER FORGET is not useful if we can't remove a node from all the
nodes of our cluster because of the Gossip protocol that keeps adding
a given node to nodes where we already tried to remove it.
So now CLUSTER FORGET implements a nodes blacklist that is set and
checked by the Gossip section processing function. This way before a
node is re-added at least 60 seconds must elapse since the FORGET
execution.
This means that redis-trib has some time to remove a node from a whole
cluster. It is possible that in the future it will be uesful to raise
the 60 sec figure to something bigger.
The rejoin delay usually is the node timeout. However if the node
timeout is too small, we set it to 500 milliseconds, that is a value
chosen to be greater than most setups RTT / instances latency figures
so that likely communication with other nodes happen before rejoining.
Usually we update the cluster state (to understand if we should accept
queries or reply with an error) only when there is a change in the state
of the nodes. However for the "delayed rejoin" feature to work, that is,
for a master to wait some time before accepting queries again after it
rejoins the majority, we need to periodically update the last time when
the node was partitioned away from the majority.
With this commit if the cluster is down we update the state ten times
per second.
Even without the user messing manually with the file, it is still
possible to have blank lines (just a single "\n" per line) because of
how the nodes.conf update/write process works.
The way the file was generated was unsafe and leaded to nodes.conf file
corruption (zero length file) on server stop/crash during the creation
of the file.
The previous file update method was as simple as open with O_TRUNC
followed by the write call. While the write call was a single one with
the full payload, ensuring no half-written files for POSIX semantics,
stopping the server just after the open call resulted into a zero-length
file (all the nodes information lost!).
A client can enter a special cluster read-only mode using the READONLY
command: if the client read from a slave instance after this command,
for slots that are actually served by the instance's master, the queries
will be processed without redirection, allowing clients to read from
slaves (but without any kind fo read-after-write guarantee).
The READWRITE command can be used in order to exit the readonly state.
The new command allows to change master-specific configurations
at runtime. All the settable parameters can be retrivied via the
SENTINEL MASTER command, so there is no equivalent "GET" command.
The claim about unlinking the instance from the connected hash tables
was the opposite of the reality. Also the current actual behavior is
safer in most cases, so it is better to manually unlink when needed.
The new function is used when we want to normalize an IP address without
performing a DNS lookup if the string to resolve is not a valid IP.
This is useful every time only IPs are valid inputs or when we want to
skip DNS resolution that is slow during runtime operations if we are
required to block.
Masters not understanding REPLCONF ACK will reply with errors to our
requests causing a number of possible issues.
This commit detects a global replication offest set to -1 at the end of
the replication, and marks the client representing the master with the
REDIS_PRE_PSYNC flag.
Note that this flag was called REDIS_PRE_PSYNC_SLAVE but now it is just
REDIS_PRE_PSYNC as it is used for both slaves and masters starting with
this commit.
This commit fixes issue #1488.
Now the socket is closed if anetNonBlock() fails, and in general the
code structure makes it harder to introduce this kind of bugs in the
future.
Reference: pull request #1059.
There were two problems with the implementation.
1) "save" was not correctly processed when no save point was configured,
as reported in issue #1416.
2) The way the code checked if an option existed in the "processed"
dictionary was wrong, as we add the element with as a key associated
with a NULL value, so dictFetchValue() can't be used to check for
existance, but dictFind() must be used, that returns NULL only if the
entry does not exist at all.
Currently replication offsets could be used into a limited way in order
to understand, out of a set of slaves, what is the one with the most
updated data. For example this comparison is possible of N slaves
were replicating all with the same master.
However the replication offset was not transferred from master to slaves
(that are later promoted as masters) in any way, so for instance if
there were three instances A, B, C, with A master and B and C
replication from A, the following could happen:
C disconnects from A.
B is turned into master.
A is switched to master of B.
B receives some write.
In this context there was no way to compare the offset of A and C,
because B would use its own local master replication offset as
replication offset to initialize the replication with A.
With this commit what happens is that when B is turned into master it
inherits the replication offset from A, making A and C comparable.
In the above case assuming no inconsistencies are created during the
disconnection and failover process, A will show to have a replication
offset greater than C.
Note that this does not mean offsets are always comparable to understand
what is, in a set of instances, since in more complex examples the
replica with the higher replication offset could be partitioned away
when picking the instance to elect as new master. However this in
general improves the ability of a system to try to pick a good replica
to promote to master.
When the configured node timeout is very small, the data validity time
(maximum data age for a slave to try a failover) is too little (ten
times the configured node timeout) when the replication link with the
master is mostly idle. In this case we'll receive some data from the
master only every server.repl_ping_slave_period to refresh the last
interaction with the master.
This commit adds to the max data validity time the slave ping period to
avoid this problem of slaves sensing too old data without a good reason.
However this max data validity time is likely a setting that should be
configurable by the Redis Cluster user in a way completely independent
from the node timeout.
This commit makes it simple to start an handshake with a specific node
address, and uses this in order to detect a node IP change and start a
new handshake in order to fix the IP if possible.
As specified in the Redis Cluster specification, when a node can reach
the majority again after a period in which it was partitioend away with
the minorty of masters, wait some time before accepting queries, to
provide a reasonable amount of time for other nodes to upgrade its
configuration.
This lowers the probabilities of both a client and a master with not
updated configuration to rejoin the cluster at the same time, with a
stale master accepting writes.
With this commit options not explicitly rewritten by CONFIG REWRITE are
not touched at all. These include new options that may not have support
for REWRITE, and other special cases like rename-command and include.
The value was otherwise undefined, so next time the node was promoted
again from slave to master, adding a slave to the list of slaves
would likely crash the server or result into undefined behavior.
Later this should be configurable from the command line but at least now
we use something more appropriate for our use case compared to the
redis-rb default timeout.
The bug could be easily triggered by:
SADD foo a b c 1 2 3 4 5 6
SDIFF foo foo
When the key was the same in two sets, an unsafe iterator was used to
check existence of elements in the same set we were iterating.
Usually this would just result into a wrong output, however with the
dict.c API misuse protection we have in place, the result was actually
an assertion failed that was triggered by the CI test, while creating
random datasets for the "MASTER and SLAVE consistency" test.
When a slave was disconnected from its master the replication offset was
reported as -1. Now it is reported as the replication offset of the
previous master, so that failover can be performed using this value in
order to try to select a slave with more processed data from a set of
slaves of the old master.
The previous fix for false positive timeout detected by master was not
complete. There is another blocking stage while loading data for the
first synchronization with the master, that is, flushing away the
current data from the DB memory.
This commit uses the newly introduced dict.c callback in order to make
some incremental work (to send "\n" heartbeats to the master) while
flushing the old data from memory.
It is hard to write a regression test for this issue unfortunately. More
support for debugging in the Redis core would be needed in terms of
functionalities to simulate a slow DB loading / deletion.
Redis hash table implementation has many non-blocking features like
incremental rehashing, however while deleting a large hash table there
was no way to have a callback called to do some incremental work.
This commit adds this support, as an optiona callback argument to
dictEmpty() that is currently called at a fixed interval (one time every
65k deletions).
Starting with Redis 2.8 masters are able to detect timed out slaves,
while before 2.8 only slaves were able to detect a timed out master.
Now that timeout detection is bi-directional the following problem
happens as described "in the field" by issue #1449:
1) Master and slave setup with big dataset.
2) Slave performs the first synchronization, or a full sync
after a failed partial resync.
3) Master sends the RDB payload to the slave.
4) Slave loads this payload.
5) Master detects the slave as timed out since does not receive back the
REPLCONF ACK acknowledges.
Here the problem is that the master has no way to know how much the
slave will take to load the RDB file in memory. The obvious solution is
to use a greater replication timeout setting, but this is a shame since
for the 0.1% of operation time we are forced to use a timeout that is
not what is suited for 99.9% of operation time.
This commit tries to fix this problem with a solution that is a bit of
an hack, but that modifies little of the replication internals, in order
to be back ported to 2.8 safely.
During the RDB loading time, we send the master newlines to avoid
being sensed as timed out. This is the same that the master already does
while saving the RDB file to still signal its presence to the slave.
The single newline is used because:
1) It can't desync the protocol, as it is only transmitted all or
nothing.
2) It can be safely sent while we don't have a client structure for the
master or in similar situations just with write(2).
The way the role change was recoded was not sane and too much
convoluted, causing the role information to be not always updated.
This commit fixes issue #1445.
When there is a master address switch, the reported role must be set to
master so that we have a chance to re-sample the INFO output to check if
the new address is reporting the right role.
Otherwise if the role was wrong, it will be sensed as wrong even after
the address switch, and for enough time according to the role change
time, for Sentinel consider the master SDOWN.
This fixes isue #1446, that describes the effects of this bug in
practice.
antirez