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Thread pool (request for review)


Worklog#246  http://askmonty.org/worklog/Server-BackLog/?tid=246  is ready
to review.   The worklog is implemented in
lp:~maria-captains/maria/5.5-threadpool, and if someone prefers to have a
one big diff, it is in the attachment(diff.diff)

It would be great if Monty, Serg (optionally Kristian if there is interest)
could take a some time to review it in the near future. The worklog has
extensive description of the implementation, might be helpful to consult it
before reviewing.

The branch currently has thread-handling=pool-if-threads as default, I found
it easier for testing.  Based on results of benchmark (see below),  it seems
to be generally performing well. So maybe we should use it as default, beta
version of 5.5 for better testing coverage . Maybe we can keep it as new
default after testing default, if there are no complains.


I also run some sysbench on 3 machines (2 Linuxes - fb-maria1 with 16 cores
and pitbull with 24 cores, and windows one with 8 cores but good IO),
results in
I used sysbench 0.4 to run some of "unit" oltp tests (point-select and
update-nokey), as well as mere "classic" OLTP-readonly and OLTP-readwrite.
All tests are run with number of concurrent clients ranging from 16 to 4096,
with warm cache, with sysbench table having 1Mio records.

The results seem to be quite different on all of the machines tested (the
machines are very different, in terms of cores, IO etc) , yet threadpool has
a positive effect on all 3 machines, and the positive effect seems to grow
with the number of cores.
Some words about how I ran the benchmarks

1. Benchmark client and server used different  CPUs - (I used 'taskset'
(Linux), or 'start /affinity' (Windows) to run benchmark client on #CPUs/4,
the rest of CPUs are used by the server). On Linuxes, I used
--thread_pool_size=<N> where N is number of cores I dedicate to server.
2.I used innodb_flush_log_at_trx_commit=0 and innodb_flush_method=
ALL_O_DIRECT to avoid extensive fsyncing, which I think is ok for the
purposes of the testing for this WL.
3. Every "write" benchmark (oltp_rw and update_nokey) started with new
server (i.e I kill mysqld, remove innodb files, and restart mysqld for each
test),whereas every "read" benchmark reused the same running server
instance.  Starting afresh with a new server on write benchmarks is done
mailnly to eliminate the effects of the purge lag.

I attach config file sysbench.ini is the one I used on fb-maria1

In case I missed to say it before, Happy Xmas and Happy New Year!

PS. Elena, we need to have some plan on testing it.
PPS. Kristian, tried to  integrate the 5.5-threadpool branch into Buildbot,
and stuck. Can you help?

Attachment: diff.diff
Description: Binary data

Attachment: sysbench.ini
Description: Binary data

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