xadd with id * generates random stream id
xadd & xtrim with approximate maxlen count may
trim stream randomly
xinfo may get random radix-tree-keys/nodes
xpending may get random idletime
xclaim: master and slave may have different
idletime in stream
Here the idea is that we do not want freeMemoryIfNeeded() to propagate a
DEL command before the script and change what happens in the script
execution once it reaches the slave. For example see this potential
issue (in the words of @soloestoy):
On master, we run the following script:
if redis.call('get','key')
then
redis.call('set','xxx','yyy')
end
redis.call('set','c','d')
Then when redis attempts to execute redis.call('set','xxx','yyy'), we call freeMemoryIfNeeded(), and the key may get deleted, and because redis.call('set','xxx','yyy') has already been executed on master, this script will be replicated to slave.
But the slave received "DEL key" before the script, and will ignore maxmemory, so after that master has xxx and c, slave has only one key c.
Note that this patch (and other related work) was authored collaboratively in
issue #5250 with the help of @soloestoy and @oranagra.
Related to issue #5250.
The conclusion, that a xread request can be answered syncronously in
case that the stream's last_id is larger than the passed last-received-id
parameter, assumes, that there must be entries present, which could be
returned immediately.
This assumption fails for empty streams that actually contained some
entries which got removed by xdel, ... .
As result, the client is answered synchronously with an empty result,
instead of blocking for new entries to arrive.
An additional check for a non-empty stream is required.
If we are going to read a large object from network
try to make it likely that it will start at c->querybuf
boundary so that we can optimize object creation
avoiding a large copy of data.
But only when the data we have not parsed is less than
or equal to ll+2. If the data length is greater than
ll+2, trimming querybuf is just a waste of time, because
at this time the querybuf contains not only our bulk.
It's easy to reproduce the that:
Time1: call `client pause 10000` on slave.
Time2: redis-benchmark -t set -r 10000 -d 33000 -n 10000.
Then slave hung after 10 seconds.
Technically speaking we don't really need to put the master client in
the clients that need to be processed, since in practice the PING
commands from the master will take care, however it is conceptually more
sane to do so.
Processing command from the master while the slave is in busy state is
not correct, however we cannot, also, just reply -BUSY to the
replication stream commands from the master. The correct solution is to
stop processing data from the master, but just accumulate the stream
into the buffers and resume the processing later.
Related to #5297.
To avoid copying buffers to create a large Redis Object which
exceeding PROTO_IOBUF_LEN 32KB, we just read the remaining data
we need, which may less than PROTO_IOBUF_LEN. But the remaining
len may be zero, if the bulklen+2 equals sdslen(c->querybuf),
in client pause context.
For example:
Time1:
python
>>> import os, socket
>>> server="127.0.0.1"
>>> port=6379
>>> data1="*3\r\n$3\r\nset\r\n$1\r\na\r\n$33000\r\n"
>>> data2="".join("x" for _ in range(33000)) + "\r\n"
>>> data3="\n\n"
>>> s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
>>> s.settimeout(10)
>>> s.connect((server, port))
>>> s.send(data1)
28
Time2:
redis-cli client pause 10000
Time3:
>>> s.send(data2)
33002
>>> s.send(data3)
2
>>> s.send(data3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
socket.error: [Errno 104] Connection reset by peer
To fix that, we should check if remaining is greater than zero.
Note: this breaks backward compatibility with Redis 4, since now slaves
by default are exact copies of masters and do not try to evict keys
independently.
Function setProtocolError just records proctocol error
details in server log, set client as CLIENT_CLOSE_AFTER_REPLY.
It doesn't care about querybuf sdsrange, because we
will do it after procotol parsing.
This is an optimization for processing pipeline, we discussed a
problem in issue #5229: clients may be paused if we apply `CLIENT
PAUSE` command, and then querybuf may grow too large, the cost of
memmove in sdsrange after parsing a completed command will be
horrible. The optimization is that parsing all commands in queyrbuf
, after that we can just call sdsrange only once.
When the element new score is the same of prev/next node, the
lexicographical order kicks in, so we can safely update the node in
place only when the new score is strictly between the adjacent nodes
but never equal to one of them.
Technically speaking we could do extra checks to make sure that even if the
score is the same as one of the adjacent nodes, we can still update on
place, but this rarely happens, so probably not a good deal to make it
more complex.
Related to #5179.
Slaves and rebooting redis may have different radix tree struct,
by different stream* config options. So propagating approximated
MAXLEN to AOF/slaves may lead to date inconsistency.
If we rewrite the MAXLEN argument as zero when no trimming
was performed, date between master and slave and aof will
be inconsistent, because `xtrim maxlen 0` means delete all
entries in stream.
User: "is there a reason why redis server logs are missing the year in
the "date time"?"
Me: "I guess I did not imagine it would be stable enough to run for
several years".
Related to #5157. The PR author correctly indentified that the check was
duplicated, but removing the second one introduces a bug that was fixed
in the past (hence the duplication). Instead we can remove the first
instance of the check without issues.
on slower machines, the active defrag test tended to fail.
although the fragmentation ratio was below the treshold, the defragger was
still in the middle of a scan cycle.
this commit changes:
- the defragger uses the current fragmentation state, rather than the cache one
that is updated by server cron every 100ms. this actually fixes a bug of
starting one excess scan cycle
- the test lets the defragger use more CPU cycles, in hope that the defrag
will be faster, but also give it more time before we give up.
The slave sends \n keepalive messages to the master while parsing the rdb,
and later sends REPLCONF ACK once a second. rarely, the master recives both
a linefeed char and a REPLCONF in the same read, \n*3\r\n$8\r\nREPLCONF\r\n...
and it tries to trim two chars (\r\n) from the query buffer,
trimming the '*' from *3\r\n$8\r\nREPLCONF\r\n...
then the master tries to process a command starting with '3' and replies to
the slave a bunch of -ERR and one +OK.
although the slave silently ignores these (prints a log message), this corrupts
the replication offset at the slave since the slave increases the replication
offset, and the master did not.
other than the fix in processInlineBuffer, i did several other improvments
while hunting this very rare bug.
- when redis replies with "unknown command" it includes a portion of the
arguments, not just the command name. so it would be easier to understand
what was recived, in my case, on the slave side, it was -ERR, but
the "arguments" were the interesting part (containing info on the error).
- about a year ago i added code in addReplyErrorLength to print the error to
the log in case of a reply to master (since this string isn't actually
trasmitted to the master), now changed that block to print a similar log
message to indicate an error being sent from the master to the slave.
note that the slave is marked as CLIENT_SLAVE only after PSYNC was received,
so this will not cause any harm for REPLCONF, and will only indicate problems
that are gonna corrupt the replication stream anyway.
- two places were c->reply was emptied, and i wanted to reset sentlen
this is a precaution (i did not actually see such a problem), since a
non-zero sentlen will cause corruption to be transmitted on the socket.
Reading the PR gave me the opportunity to better specify what the code
was doing in places where I was not immediately sure about what was
going on. Moreover I documented the structure in server.h so that people
reading the header file will immediately understand what the structure
is useful for.
A) slave buffers didn't count internal fragmentation and sds unused space,
this caused them to induce eviction although we didn't mean for it.
B) slave buffers were consuming about twice the memory of what they actually needed.
- this was mainly due to sdsMakeRoomFor growing to twice as much as needed each time
but networking.c not storing more than 16k (partially fixed recently in 237a38737).
- besides it wasn't able to store half of the new string into one buffer and the
other half into the next (so the above mentioned fix helped mainly for small items).
- lastly, the sds buffers had up to 30% internal fragmentation that was wasted,
consumed but not used.
C) inefficient performance due to starting from a small string and reallocing many times.
what i changed:
- creating dedicated buffers for reply list, counting their size with zmalloc_size
- when creating a new reply node from, preallocate it to at least 16k.
- when appending a new reply to the buffer, first fill all the unused space of the
previous node before starting a new one.
other changes:
- expose mem_not_counted_for_evict info field for the benefit of the test suite
- add a test to make sure slave buffers are counted correctly and that they don't cause eviction
We don't want to increment the deliveries here, because the sysadmin
reset the consumer group so the desire is likely to restart processing,
and having the PEL polluted with old information is not useful but
probably confusing.
Related to #5111.
To simplify the semantics of blocking for a group, this commit changes
the implementation to better match the description we provide of
conusmer groups: blocking for > will make the consumer waiting for new
elements in the group. However blocking for any other ID will always
serve the local history of the consumer.
However it must be noted that the > ID is actually an alias for the
special ID ms/seq of UINT64_MAX,UINT64_MAX.
To detect when the group (or the whole key) is destroyed to send an
error to the consumers blocked in such group is a problem, so we leave
the consumers listening, the sysadmin is free to create or destroy
groups assuming she/he knows what to do. However a client may be blocked
in a given consumer group, that is later destroyed. Then the stream
receives new elements. In that case there is no sane behavior to serve
the consumer... but to report an error about the group no longer
existing.
More about detecting this synchronously and why it is not done:
1. Normally we don't do that, we leave clients blocked for other data
types such as lists.
2. When we free a stream object there is no longer information about
what was the key it was associated with, so while destroying the
consumer groups we miss the info to unblock the clients in that moment.
3. Objects can be reclaimed in other threads where it is no longer safe
to do client operations.
When a client blocks for a consumer group, we don't know the actual ID
we want to be served: other clients blocked in the same consumer group
may be served first, so the consumer group latest delivered ID changes.
This was not handled correctly, all the clients in the consumer group
were unblocked without data but the first.
With such information will be able to use a private localtime()
implementation serverLog(), which does not use any locking and is both
thread and fork() safe.
Salvatore Sanfilippo