Re: Postgresql JDBC process consumes more memory with partition tables update delete

On Thu, 8 Sept 2022 at 08:05, James Pang (chaolpan) <chaolpan(at)cisco(dot)com>
wrote:

> Hi,
> When I convert the partitioned table to non-partitioned and copy all
> data to non-partitioned tables, then restart the load test , one backend
> server only consumes 25mb there. With partitioned tables ,
> PGV13 , 160-170mb /per backend server, PGV14, 130-138mb/per backend
> server. So , it's partitioned tables make the memory consumption changes.
> The dumped stats is backend(session) level cached plans ,right? The test
> servers use shared connection pooling to run same insert/update/delete
> transaction by multiple connections(we simulate 300 connections) , so each
> session see similar cached SQL plans, and part of table has trigger before
> UPDATE, so when UPDATE it trigger to call pl/pgsql function. Another
> thing is even after the backend server idle there long time, it's still
> keep the same memory without release back to OS.
>

If you are using a connection pool, then the connections aren't closed so I
don't see this an issue.

Dave

> I only use psql to make same prepared SQL and run that in a loop, I see
> stable memory usage, maybe my psql test is not same as the JAVA test code.
> I will check the test code details and try to check if possible to dump
> more context details.
>
> Thanks,
>
> James
>
>
> -----Original Message-----
> From: Vladimir Sitnikov <sitnikov(dot)vladimir(at)gmail(dot)com>
> Sent: Thursday, September 8, 2022 5:56 PM
> To: James Pang (chaolpan) <chaolpan(at)cisco(dot)com>
> Cc: pgsql-jdbc(at)lists(dot)postgresql(dot)org
> Subject: Re: Postgresql JDBC process consumes more memory with partition
> tables update delete
>
> > interesting thing is we only see this issue by JDBC driver client
>
> First of all, it turns out that a single UPDATE statement consumes 4M
>
> Then, it looks like you have **multiple** UPDATE statements in the
> server-side cache.
> It does sound strange that a single backend contains multiple entries for
> the same SQL text.
>
> 1) Would you please double-check that SQL text is the same. Do you use
> bind variables?
> 2) Would you please double-check that you close statements after use (e.g.
> try-with-resources).
>
>
> CachedPlan: 4204544 total in 13 blocks; 489400 free (4 chunks);
> 3715144 used: UPDATE WBXMEETINGINS
>
> Frankly speaking, I am not sure the JDBC driver is in a position to
> predict that a single-line statement would consume that much server-side
> memory.
>
> It would be nice if backend devs could optimize the memory consumption of
> the cached plan.
> If optimization is not possible, then it would be nice if the backend
> could provide clients with memory consumption of the cached plan.
> In other words, it would be nice if there was a status message or
> something that says "ok, by the way, the prepared statement S_01 consumes
> 2M".
>
> James, the captured dump includes only the first 100 entries.
> Would you please try capturing more details via the following command?
>
> MemoryContextStatsDetail(TopMemoryContext, 1000, true)
>
> (see
> https://github.com/postgres/postgres/blob/adb466150b44d1eaf43a2d22f58ff4c545a0ed3f/src/backend/utils/mmgr/mcxt.c#L574-L591
> )
>
>
> Vladimir
>