Re: postgres 9.3 vs. 9.4

On 18/09/14 21:58, Mkrtchyan, Tigran wrote:
>
>
> Hi Folk,
>
> I am trying to investigate some performance issues which we have with postgres
> (a different topic by itself) and tried postgres.9.4beta2, with a hope that it
> perform better.
>
> Turned out that 9.4 is 2x slower than 9.3.5 on the same hardware.
>
> Some technical details:
>
> Host: rhel 6.5 2.6.32-431.23.3.el6.x86_64
> 256 GB RAM, 40 cores, Intel(R) Xeon(R) CPU E5-2660 v2 @ 2.20GHz
> 2x160GB PCIe SSD DELL_P320h-MTFDGAL175SAH ( on one 9.3, on an other one 9.4 )
>
> postgres tweaks:
>
>
> default_statistics_target = 100
> wal_writer_delay = 10s
> vacuum_cost_delay = 50
> synchronous_commit = off
> maintenance_work_mem = 2GB
> checkpoint_completion_target = 0.9
> effective_cache_size = 94GB
> work_mem = 402MB
> wal_buffers = 16MB
> checkpoint_segments = 64
> shared_buffers = 8GB
> max_connections = 100
> random_page_cost = 1.5
> # other goodies
> log_line_prefix = '%m <%d %u %r> %%'
> log_temp_files = 0
> log_min_duration_statement = 5
>
> in both cases databases are fresh - no data.
>
> Here is a results with pgbench.
>
>
> 9.3.5:
>
> # /usr/pgsql-9.3/bin/pgbench -r -j 1 -c 1 -T 60
> starting vacuum...end.
> transaction type: TPC-B (sort of)
> scaling factor: 1
> query mode: simple
> number of clients: 1
> number of threads: 1
> duration: 60 s
> number of transactions actually processed: 96361
> tps = 1605.972262 (including connections establishing)
> tps = 1606.064501 (excluding connections establishing)
> statement latencies in milliseconds:
> 0.001391 \set nbranches 1 * :scale
> 0.000473 \set ntellers 10 * :scale
> 0.000430 \set naccounts 100000 * :scale
> 0.000533 \setrandom aid 1 :naccounts
> 0.000393 \setrandom bid 1 :nbranches
> 0.000468 \setrandom tid 1 :ntellers
> 0.000447 \setrandom delta -5000 5000
> 0.025161 BEGIN;
> 0.131317 UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
> 0.100211 SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
> 0.117406 UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
> 0.114332 UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
> 0.086660 INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
> 0.035940 END;
>
>
> 9.4beta2:
>
> # /usr/pgsql-9.3/bin/pgbench -r -j 1 -c 1 -T 60
> starting vacuum...end.
> transaction type: TPC-B (sort of)
> scaling factor: 1
> query mode: simple
> number of clients: 1
> number of threads: 1
> duration: 60 s
> number of transactions actually processed: 34017
> tps = 566.948384 (including connections establishing)
> tps = 567.008666 (excluding connections establishing)
> statement latencies in milliseconds:
> 0.001879 \set nbranches 1 * :scale
> 0.000526 \set ntellers 10 * :scale
> 0.000490 \set naccounts 100000 * :scale
> 0.000595 \setrandom aid 1 :naccounts
> 0.000421 \setrandom bid 1 :nbranches
> 0.000480 \setrandom tid 1 :ntellers
> 0.000484 \setrandom delta -5000 5000
> 0.055047 BEGIN;
> 0.172179 UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
> 0.135392 SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
> 0.157224 UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
> 0.147969 UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
> 0.123001 INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
> 0.957854 END;
>
> any ideas?
>

Hi Tigran,

Some ideas:

60s is too short for reliable results (default settings for checkpoints
is 300s so 600s is the typical elapsed time to get reasonably repeatable
numbers (to ensure you get about 1 checkpoint in your run). In addition
I usually do

psql <<!
CHECKPOINT;
!

Plus

$ sleep 10

before each run so that I've got some confidence that we are starting
from approximately the same state each time (and getting hopefully only
*one* checkpoint per run)!

Cheers

Mark