CLUSTER SLOTS now includes IDs in the nodes description associated with
a given slot range. Certain client libraries implementations need a way
to reference a node in an unique way, so they were relying on CLUSTER
NODES, that is not a stable API and may change frequently depending on
Redis Cluster future requirements.
The change covers the case where:
1. There is a node we can't reach (in fail or pfail state).
2. We see a different address for this node, in the gossip section sent
to us by a node that, instead, is able to talk with the node we cannot
talk to.
In this case it's a good bet to switch to the address reported by this
node, since there was an address switch and it is able to talk with the
node and we are not.
However previosuly this was done in a dangerous way, by initiating an
handshake. The handshake, using the MEET packet, forces the receiver to
join our cluster, and this is not a good idea. If the node in question
really just switched address, but is the same node, it already knows about
us, so we just need to perform an address update and a reconnection.
So with this commit instead we just update the address of the node,
release the node link if any, and attempt to reconnect in the next
clusterCron() cycle.
The commit also improves debugging messages printed by Cluster during
address or ID switches.
Another leak was fixed in the case of syntax error by restructuring the
allocation strategy for the two dynamic vectors.
We also make sure to always close the cached socket on I/O errors so that
all the I/O errors are handled the same, even if we had a previously
queued error of a different kind from the destination server.
Thanks to Kevin McGehee. Related to issue #3016.
In issue #3016 Kevin McGehee identified multiple very serious issues in
the new implementation of MIGRATE. This commit attempts to restructure
the code in oder to avoid mistakes, an analysis of the new
implementation is in progress in order to check for possible edge cases.
With this commit we preserve the list of nodes that have .slaveof set
to the node, even when the node is turned into a slave, and make sure to
fix the .slaveof pointers to NULL when a node is freed from memory,
regardless of the fact it's a slave or a master.
Basically we try to remember the logical master in the current
configuration even if the logical master advertised it as a slave
already. However we still remember the associations, so that when a node
is freed we can fix them.
This should fix issue #3002.
Sometimes during "fixes" we have to setup a new configuration and assign
slots to nodes. With BUMPEPOCH we can make sure the new configuration of
the node will win if there are conflicting configurations (for example
another node is *also* claiming the same slot because the cluster is
totally messed up).
Extend the MIGRATE extra freedom to be able to be called in the context
of the local slot, anytime there is a slot open in one or the other
direction (importing or migrating). This is useful for redis-trib to fix
the cluster when it has in an odd state.
Thix fix allows "redis-trib fix" to make its work in certain cases where
previously an error was reported.
For non existing keys, we don't want to send -ASK redirections to
MIGRATE, since when moving slots from the migrating node to the
importing node, we want just to ignore keys that are no longer there.
They may be expired or deleted between the GETKEYSINSLOT call and the
MIGRATE call. Otherwise this causes an error during migrations with
redis-trib (or equivalent cluster management tools).
We need to process replies after errors in order to delete keys
successfully transferred. Also argument rewriting was fixed since
it was broken in several ways. Now a fresh argument vector is created
and set if we are acknowledged of at least one key.
We wait a fixed amount of time (5 seconds currently) much greater than
the usual Cluster node to node communication latency, before migrating.
This way when a failover occurs, before detecting the new master as a
target for migration, we give the time to its natural slaves (the slaves
of the failed over master) to announce they switched to the new master,
preventing an useless migration operation.
Some time ago I broken replicas migration (reported in #2924).
The idea was to prevent masters without replicas from getting replicas
because of replica migration, I remember it to create issues with tests,
but there is no clue in the commit message about why it was so
undesirable.
However my patch as a side effect totally ruined the concept of replicas
migration since we want it to work also for instances that, technically,
never had slaves in the past: promoted slaves.
So now instead the ability to be targeted by replicas migration, is a
new flag "migrate-to". It only applies to masters, and is set in the
following two cases:
1. When a master gets a slave, it is set.
2. When a slave turns into a master because of fail over, it is set.
This way replicas migration targets are only masters that used to have
slaves, and slaves of masters (that used to have slaves... obviously)
and are promoted.
The new flag is only internal, and is never exposed in the output nor
persisted in the nodes configuration, since all the information to
handle it are implicit in the cluster configuration we already have.
There was a bug in Redis Cluster caused by clients blocked in a blocking
list pop operation, for keys no longer handled by the instance, or
in a condition where the cluster became down after the client blocked.
A typical situation is:
1) BLPOP <somekey> 0
2) <somekey> hash slot is resharded to another master.
The client will block forever int this case.
A symmentrical non-cluster-specific bug happens when an instance is
turned from master to slave. In that case it is more serious since this
will desynchronize data between slaves and masters. This other bug was
discovered as a side effect of thinking about the bug explained and
fixed in this commit, but will be fixed in a separated commit.
This commit moves the process of generating a new config epoch without
consensus out of the clusterCommand() implementation, in order to make
it reusable for other reasons (current target is to have a CLUSTER
FAILOVER option forcing the failover when no master majority is
reachable).
Moreover the commit moves other functions which are similarly related to
config epochs in a new logical section of the cluster.c file, just for
clarity.
Before we relied on the global cluster state to make sure all the hash
slots are linked to some node, when getNodeByQuery() is called. So
finding the hash slot unbound was checked with an assertion. However
this is fragile. The cluster state is often updated in the
clusterBeforeSleep() function, and not ASAP on state change, so it may
happen to process clients with a cluster state that is 'ok' but yet
certain hash slots set to NULL.
With this commit the condition is also checked in getNodeByQuery() and
reported with a identical error code of -CLUSTERDOWN but slightly
different error message so that we have more debugging clue in the
future.
Root cause of issue #2288.
1. Remove useless "cs" initialization.
2. Add a "select" var to capture a condition checked multiple times.
3. Avoid duplication of the same if (!copy) conditional.
4. Don't increment dirty if copy is given (no deletion is performed),
otherwise we propagate MIGRATE when not needed.
This improves PFAIL -> FAIL switch. Too late at this point in the RC
releases to add proper PFAIL/FAIL separate dictionary to do this in a
less randomized way. Tested in practice with experiments that this
helps. PFAIL -> FAIL average with 20 nodes and node-timeout set to 5
seconds takes 2.5 seconds without this commit, 1 second with this
commit.
Otherwise it is impossible to receive the majority of failure reports in
the node_timeout*2 window in larger clusters.
Still with a 200 nodes cluster, 20 gossip sections are a very reasonable
amount of bytes to send.
A side effect of this change is also fater cluster nodes joins for large
clusters, because the cluster layout makes less time to propagate.
Otherwise we risk sending not initialized data to other nodes, that may
contain anything. This was actually not possible only because the
initialization of the buffer where the cluster packets header is created
was larger than the 3 gossip sections we use, so the memory was already
all filled with zeroes by the memset().
Fixes valgrind error:
48 bytes in 1 blocks are definitely lost in loss record 196 of 373
at 0x4910D3: je_malloc (jemalloc.c:944)
by 0x42807D: zmalloc (zmalloc.c:125)
by 0x41FA0D: dictGetIterator (dict.c:543)
by 0x41FA48: dictGetSafeIterator (dict.c:555)
by 0x459B73: clusterHandleSlaveMigration (cluster.c:2776)
by 0x45BF27: clusterCron (cluster.c:3123)
by 0x423344: serverCron (redis.c:1239)
by 0x41D6CD: aeProcessEvents (ae.c:311)
by 0x41D8EA: aeMain (ae.c:455)
by 0x41A84B: main (redis.c:3832)
If array has N elements, we can't read +1 if we are already at N.
Also, we need to move elements by their storage size in the array,
not just by individual bytes.
[maybe] Fixes valgrind errors:
32 bytes in 4 blocks are definitely lost in loss record 107 of 228
at 0x80EA447: je_malloc (jemalloc.c:944)
by 0x806E59C: zrealloc (zmalloc.c:125)
by 0x80A9AFC: clusterSetMaster (cluster.c:801)
by 0x80AEDC9: clusterCommand (cluster.c:3994)
by 0x80682A5: call (redis.c:2049)
by 0x8068A20: processCommand (redis.c:2309)
by 0x8076497: processInputBuffer (networking.c:1143)
by 0x8073BAF: readQueryFromClient (networking.c:1208)
by 0x8060E98: aeProcessEvents (ae.c:412)
by 0x806123B: aeMain (ae.c:455)
by 0x806C3DB: main (redis.c:3832)
64 bytes in 8 blocks are definitely lost in loss record 143 of 228
at 0x80EA447: je_malloc (jemalloc.c:944)
by 0x806E59C: zrealloc (zmalloc.c:125)
by 0x80AAB40: clusterProcessPacket (cluster.c:801)
by 0x80A847F: clusterReadHandler (cluster.c:1975)
by 0x30000FF: ???
80 bytes in 10 blocks are definitely lost in loss record 148 of 228
at 0x80EA447: je_malloc (jemalloc.c:944)
by 0x806E59C: zrealloc (zmalloc.c:125)
by 0x80AAB40: clusterProcessPacket (cluster.c:801)
by 0x80A847F: clusterReadHandler (cluster.c:1975)
by 0x2FFFFFF: ???
Fixes valgrind error:
Syscall param write(buf) points to uninitialised byte(s)
at 0x514C35D: ??? (syscall-template.S:81)
by 0x456B81: clusterWriteHandler (cluster.c:1907)
by 0x41D596: aeProcessEvents (ae.c:416)
by 0x41D8EA: aeMain (ae.c:455)
by 0x41A84B: main (redis.c:3832)
Address 0x5f268e2 is 2,274 bytes inside a block of size 8,192 alloc'd
at 0x4932D1: je_realloc (jemalloc.c:1297)
by 0x428185: zrealloc (zmalloc.c:162)
by 0x4269E0: sdsMakeRoomFor.part.0 (sds.c:142)
by 0x426CD7: sdscatlen (sds.c:251)
by 0x4579E7: clusterSendMessage (cluster.c:1995)
by 0x45805A: clusterSendPing (cluster.c:2140)
by 0x45BB03: clusterCron (cluster.c:2944)
by 0x423344: serverCron (redis.c:1239)
by 0x41D6CD: aeProcessEvents (ae.c:311)
by 0x41D8EA: aeMain (ae.c:455)
by 0x41A84B: main (redis.c:3832)
Uninitialised value was created by a stack allocation
at 0x457810: nodeUpdateAddressIfNeeded (cluster.c:1236)
read() and write() return ssize_t (signed long), not int.
For other offsets, we can use the unsigned size_t type instead
of a signed offset (since our replication offsets and buffer
positions are never negative).
In order to avoid that misconfigured cluster nodes at some time may
force an IP update on other nodes, it is required that nodes update
their own address only on MEET messages. However it does not make sense
to do this the first time a node is contacted and yet does not have an
IP, we just risk that myself->ip remains not assigned if there are
messages lost or cluster creation procedures that don't make sure
everybody is targeted by at least one incoming MEET message.
Also fix the logging of the IP switch avoiding the :-1 tail.
Also explicitly set version to 0, add a protocol version define, improve
comments in the gossip structure.
Note that the structure layout is the same after the change, we are just
making the padding explicit with an additional not used 16 bits field.
So this commit is still able to talk with the previous versions of
cluster nodes.
Valgrind checks that the buffers we transfer via syscalls are all
composed of bytes actually initialized. This is useful, it makes we able
to avoid leaking informations in non initialized parts fo messages
transferred to other hosts. This commit fixes one of such issues.
Can't be initialized by resetManualFailover() since it's actual state
the function uses, so we need to initialize it at startup time. Not
really a bug in practical terms, but showed up into valgrind and is not
technically correct anyway.
If we woke up to accept a connection, but we can't
accept it, inform the user of the error going on
with their networking.
(The previous message was the same for success or error!)
Slaves key expire is orchestrated by the master. Sometimes the master
will send the synthesized DEL to expire keys on the slave with a non
trivial delay (when the key is not accessed, only the incremental expiry
algorithm will expire it in background).
During that time, a key is logically expired, but slaves still return
the key if you GET (or whatever) it. This is a bad behavior.
However we can't simply trust the slave view of the key, since we need
the master to be able to send write commands to update the slave data
set, and DELs should only happen when the key is expired in the master
in order to ensure consistency.
However 99.99% of the issues with this behavior is when a client which
is not a master sends a read only command. In this case we are safe and
can consider the key as non existing.
This commit does a few changes in order to make this sane:
1. lookupKeyRead() is modified in order to return NULL if the above
conditions are met.
2. Calls to lookupKeyRead() in commands actually writing to the data set
are repliaced with calls to lookupKeyWrite().
There are redundand checks, so for example, if in "2" something was
overlooked, we should be still safe, since anyway, when the master
writes the behavior is to don't care about what expireIfneeded()
returns.
This commit is related to #1768, #1770, #2131.
bulk_data field size was not removed from the count. It is not possible
to declare it simply as 'char bulk_data[]' since the structure is nested
into another structure.
Same as the original bind fixes (we just missed these the
first time around).
This helps Redis not automatically send
connections from the first IP on an interface if we are bound
to a specific IP address (e.g. with multiple IP aliases on one
interface, you want to send from _your_ IP, not from the first IP
on the interface).
With the exception of nodes sending MEET packets: we have to trust them
since they can send us MEET packets only when the cluster is initially
created or because sysadmin manual action.
In the cluster evaluation function we are supposed to set the cluster
state as "fail" if we are among a minority, however the code was not
detecting to be into a minority partition if exactly half the masters
were reachable, which is a minority.
- Remove trailing newlines from redis.conf
- Fix comment misspelling
- Clarifies zipEncodeLength usage and a C API mention (#1243, #1242)
- Fix cluster typos (inspired by @papanikge #1507)
- Fix rewite -> rewrite in a few places (inspired by #682)
Closes#1243, #1242, #1507
This fixes a potential bug that was never observed in practice since
what happens is that the asynchronous connect returns ok (to fail later,
calling the handler) every time, so a ping is queued, and sent_ping
happens to always be populated.
Howver technically connect(2) with a non blocking socket may return an
error synchronously, so before this fix the code was not correct.
This commit adds a size check after initial config
line parsing to make sure we have *at least* 8 arguments
per line.
Also, instead of asserting for cluster->myself, we just test
and error out normally (since the error does a hard exit anyway).
Closes#1597
The funciton was also modified in order to be more standalone and
produce an output without trailing spaces, making the reuse simpler.
The global variable was renamed in cammel case as most other Redis
globals, except the main ones we refer too many times, like 'server'.
Replica migration algorithm modified so that slaves never try to migrate
to masters that were never configured to have slaves in the past.
We want the algorithm to take care of masters that remained without
*working* slaves, but that used to have slaves according to the cluster
configuration.
For non-empty masters, CLUSTER RESET is denied, and the user requires to
start to reset a node by explicitly clearing it with FLUSHALL.
However CLUSTER RESET when executed with slaves don't have this
restrictions since data is just a replica of the master, and with
read-only slaves it is also not possible to remove the data set. However
the node was turned from slave to master after a reset, without touching
the old slave data. This is 99.99% of times not appropriate and forces
full resets to follow this path to work with both slave and master
nodes:
FLUSHALL
CLUSTER RESET HARD
FLUSHALL
Since we need the first flushall for masters, and the second for slaves.
This commit changes the behavior so that CLUSTER RESET removes the data set
of a slave node during a reset, in the moment it gets turned into a master,
so the new pattern is simply:
FLUSHALL (that may fail for slaves)
CLUSTER RESET
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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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 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.
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.
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.
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.
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.
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 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.
antirez