Re: BUG #15712: latency delay for first query execution in PostgreSQL DB 11

Hi

po 25. 3. 2019 v 10:02 odesílatel PG Bug reporting form <
noreply(at)postgresql(dot)org> napsal:

> The following bug has been logged on the website:
>
> Bug reference: 15712
> Logged by: Sandeep Kumar
> Email address: sandeep(dot)t(dot)kumar(at)gmail(dot)com
> PostgreSQL version: 11.0
> Operating system: Windows
> Description:
>
> Delay of query execution due to latency on PostgreSQL DB 11 and this is
> happening for first query execution and rest of queries going smooth.
>

it can be expected. Postgres has session based cache of metadata. So first
query in session has higher overhead due empty metadata cache.

Regards

Pavel Stehule

> Following are the test result from JMeter with 5 concurrent users ,
> please
> observed the Latency for first 5.
>
> Start time Thread Label Sampletime
>
> Bytes Latency Connect time(ms)
> =========================================================================
> 1 04:15:43.473 Postgres 1-1 SQL1_PG 73 Success 58544 1
> 0
> 2 04:15:43.673 Postgres 1-2 SQL1_PG 357 Success 58544
> 166 0
> 3 04:15:43.874 Postgres 1-3 SQL1_PG 362 Success 58544
> 156 0
> 4 04:15:44.075 Postgres 1-4 SQL1_PG 365 Success 58544
> 161 0
> 5 04:15:44.275 Postgres 1-5 SQL1_PG 236 Success 58544
> 165 0
> 6 04:15:43.546 Postgres 1-1 SQL2_PG 138 Success 40336 0
> 0
> 7 04:15:44.929 Postgres 1-1 SQL3_PG 324 Success 165650 0
> 0
> 8 04:15:44.031 Postgres 1-2 SQL2_PG 1266 Success 40336 0
> 0
> 9 04:15:45.298 Postgres 1-2 SQL3_PG 325 Success 165650 0
> 0
> 10 04:15:44.236 Postgres 1-3 SQL2_PG 1415 Success 40336 0
> 0
> 11 04:15:44.440 Postgres 1-4 SQL2_PG 1269 Success 40336 0
> 0
> 12 04:15:44.512 Postgres 1-5 SQL2_PG 1269 Success 40336 0
> 0
> 13 04:15:45.651 Postgres 1-3 SQL3_PG 353 Success 165650 0
> 0
> 14 04:15:45.709 Postgres 1-4 SQL3_PG 339 Success 165650 1
> 0
> 15 04:15:45.781 Postgres 1-5 SQL3_PG 325 Success 165650 1
> 0
> 16 04:15:45.254 Postgres 1-1 SQL4_PG 999 Success 15935 0
> 0
> 17 04:15:46.254 Postgres 1-1 SQL5_PG 174 Success 23208 0
> 0
> 18 04:15:45.623 Postgres 1-2 SQL4_PG 948 Success 15935 0
> 0
> 19 04:15:46.572 Postgres 1-2 SQL5_PG 169 Success 23208 0
> 0
> 20 04:15:46.005 Postgres 1-3 SQL4_PG 1018 Success 15935 0
> 0
> 21 04:15:46.107 Postgres 1-5 SQL4_PG 916 Success 15935 0
> 0
> 22 04:15:46.049 Postgres 1-4 SQL4_PG 985 Success 15935 0
> 0
> 23 04:15:47.023 Postgres 1-3 SQL5_PG 212 Success 23208 0
> 0
> 24 04:15:47.035 Postgres 1-4 SQL5_PG 200 Success 23208 0
> 0
> 25 04:15:47.024 Postgres 1-5 SQL5_PG 211 Success 23208 0
> 0
>
>