Re: [PATCH] Reuse Workers and Replication Slots during Logical Replication

On Fri, Aug 11, 2023 at 11:45 PM Melih Mutlu <m(dot)melihmutlu(at)gmail(dot)com> wrote:
>
> Again, I couldn't reproduce the cases where you saw significantly degraded performance. I wonder if I'm missing something. Did you do anything not included in the test scripts you shared? Do you think v26-0001 will perform 84% worse than HEAD, if you try again? I just want to be sure that it was not a random thing.
> Interestingly, I also don't see an improvement in above results as big as in your results when inserts/tx ratio is smaller. Even though it certainly is improved in such cases.
>

TEST ENVIRONMENTS

I am running the tests on a high-spec machine:

-- NOTE: Nobody else is using this machine during our testing, so
there are no unexpected influences messing up the results.

Linix

Architecture: x86_64
CPU(s): 120
Thread(s) per core: 2
Core(s) per socket: 15

total used free shared buff/cache available
Mem: 755G 5.7G 737G 49M 12G 748G
Swap: 4.0G 0B 4.0G

~~~

The results I am seeing are not random. HEAD+v26-0001 is consistently
worse than HEAD but only for some settings. With these settings, I see
bad results (i.e. worse than HEAD) consistently every time using the
dedicated test machine.

Hou-san also reproduced bad results using a different high-spec machine

Vignesh also reproduced bad results using just his laptop but in his
case, it did *not* occur every time. As discussed elsewhere the
problem is timing-related, so sometimes you may be lucky and sometimes
not.

~

I expect you are running everything correctly, but if you are using
just a laptop (like Vignesh) then like him you might need to try
multiple times before you can hit the problem happening in your
environment.

Anyway, in case there is some other reason you are not seeing the bad
results I have re-attached scripts and re-described every step below.

======

BUILDING

-- NOTE: I have a very minimal configuration without any
optimization/debug flags etc. See config.log

$ ./configure --prefix=/home/peter/pg_oss

-- NOTE: Of course, make sure to be running using the correct Postgres:

echo 'set environment variables for OSS work'
export PATH=/home/peter/pg_oss/bin:$PATH

-- NOTE: Be sure to do git stash or whatever so don't accidentally
build a patched version thinking it is the HEAD version
-- NOTE: Be sure to do a full clean build and apply (or don't apply
v26-0001) according to the test you wish to run.

STEPS
1. sudo make clean
2. make
3. sudo make install

======

SCRIPTS & STEPS

SCRIPTS
testrun.sh
do_one_test_setup.sh
do_one_test_PUB.sh
do_one_test_SUB.sh

---

STEPS

Step-1. Edit the testrun.sh

tables=( 100 )
workers=( 2 4 8 16 )
size="0"
prefix="0816headbusy" <-- edit to differentiate each test run

~

Step-2. Edit the do_one_test_PUB.sh
IF commit_counter = 1000 THEN <-- edit this if needed. I wanted 1000
inserts/tx so nothing to do

~

Step-3: Check nothing else is running. If yes, then clean it up
[peter(at)localhost testing_busy]$ ps -eaf | grep postgres
peter 111924 100103 0 19:31 pts/0 00:00:00 grep --color=auto postgres

~

Step-4: Run the tests
[peter(at)localhost testing_busy]$ ./testrun.sh
num_tables=100, size=0, num_workers=2, run #1 <-- check the echo
matched the config you set in the Setp-1
waiting for server to shut down.... done
server stopped
waiting for server to shut down.... done
server stopped
num_tables=100, size=0, num_workers=2, run #2
waiting for server to shut down.... done
server stopped
waiting for server to shut down.... done
server stopped
num_tables=100, size=0, num_workers=2, run #3
...

~

Step-5: Sanity check
When the test completes the current folder will be full of .log and .dat* files.
Check for sanity that no errors happened

[peter(at)localhost testing_busy]$ cat *.log | grep ERROR
[peter(at)localhost testing_busy]$

~

Step-6: Collect the results
The results are output (by the do_one_test_SUB.sh) into the *.dat_SUB files
Use grep to extract them

[peter(at)localhost testing_busy]$ cat 0816headbusy_100t_0_2w_*.dat_SUB |
grep RESULT | grep -v duration | awk '{print $3}'
11742.019
12157.355
11773.807
11582.981
12220.962
12546.325
12210.713
12614.892
12015.489
13527.05

Repeat grep for other files:
$ cat 0816headbusy_100t_0_4w_*.dat_SUB | grep RESULT | grep -v
duration | awk '{print $3}'
$ cat 0816headbusy_100t_0_8w_*.dat_SUB | grep RESULT | grep -v
duration | awk '{print $3}'
$ cat 0816headbusy_100t_0_16w_*.dat_SUB | grep RESULT | grep -v
duration | awk '{print $3}'

~

Step-7: Summarise the results
Now I just cut/paste the results from Step-6 into a spreadsheet and
report the median of the runs.

For example, for the above HEAD run, it was:
2w 4w 8w 16w
1 11742 5996 1919 1582
2 12157 5960 1871 1469
3 11774 5926 2101 1571
4 11583 6155 1883 1671
5 12221 6310 1895 1707
6 12546 6166 1900 1470
7 12211 6114 2477 1587
8 12615 6173 2610 1715
9 12015 5869 2110 1673
10 13527 5913 2144 1227
Median 12184 6055 2010 1584

~

Step-8: REPEAT
-- repeat all above for different size transactions (editing do_one_test_PUB.sh)
-- repeat all above after rebuilding again with HEAD+v26-0001

------
Kind Regards,
Peter Smith.
Fujitsu Australia