b640e2944 added a test that now fails with valgrind
it fails for two resons:
1) the test samples the used memory and then limits the maxmemory to
that value, but it turns out this is not atomic and on slow machines
the background cron process that clean out old query buffers reduces
the memory so that the setting doesn't cause eviction.
2) the dbsize was tested late, after reading some invalidation messages
by that time more and more keys got evicted, partially draining the
db. this is not the focus of this fix (still a known limitation)
(cherry picked from commit 080ad5b0f297bc91f38cf49a7ff25605f4fcbe64)
When client tracking is enabled signalModifiedKey can increase memory usage,
this can cause the loop in performEvictions to keep running since it was measuring
the memory usage impact of signalModifiedKey.
The section that measures the memory impact of the eviction should be just on dbDelete,
excluding keyspace notification, client tracking, and propagation to AOF and replicas.
This resolves part of the problem described in #8069
p.s. fix took 1 minute, test took about 3 hours to write.
(cherry picked from commit b640e2944e42759412ac67228cf64c43dfbed9c3)
solving few replication related tests race conditions which fail on slow machines
bugfix in slave buffers test: since the test is executed twice, each time with
a different commands count, the threshold for the delta can't be a constant.
Few tests had borderline thresholds that were adjusted.
The slave buffers test had two issues, preventing the slave buffer from growing:
1) the slave didn't necessarily go to sleep on time, or woke up too early,
now using SIGSTOP to make sure it goes to sleep exactly when we want.
2) the master disconnected the slave on timeout
it looks like on slow machines we're getting:
[err]: slave buffer are counted correctly in tests/unit/maxmemory.tcl
Expected condition '$slave_buf > 2*1024*1024' to be true (16914 > 2*1024*1024)
this is a result of the slave waking up too early and eating the
slave buffer before the traffic and the test ends.
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
