[debian-mysql] Bug#1027337: Bug#1027337: mariadb-server-10.5: Huge increase in memory consumption (leak?) since upgrade from 10.5.15 to 10.5.18

[Matteo Valsasna]

Thanks a lot Faustin



I found an useful description of MDEV-29988 in a comment to one of its duplicates, and it matches quite well our application scenario for the database connection that cause the memory leak according to information_schema.PROCESSLIST.memory_used
(prepared statements executed maaany times, string comparisons)

we reproduced the issue on a test machine, and we will try to downgrade to 10.5.15



MAtteo



https://jira.mariadb.org/browse/MDEV-30096?focusedCommentId=243814&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-243814

[serg]Sergei Golubchik<https://jira.mariadb.org/secure/ViewProfile.jspa?name=serg> added a comment - 2022-11-28 22:20

Yes, <https://jira.mariadb.org/browse/MDEV-29988>  was in 10.6.11 too. But let's first check the preconditions:

  *   you use prepared statements
  *   you prepare once and then execute many thousands of times before deallocating the statement
  *   your statements contains a string comparison with strings in different (but compatible) character sets (e.g. utf8 and latin1).

if all that matches your use case you could be affected by <https://jira.mariadb.org/browse/MDEV-29988> . If you do, then

  *   every execution of such a prepared statements will allocate more memory
  *   all memory will be freed when a statements is deallocated (explicitly or when the client disconnects)
  *   time to deallocate a prepared statement is proportional to the number of times it was executed

and workarounds could be

  *   deallocate prepared statements more often
  *   rewrite statements to avoid comparing strings in different character sets

or wait for the next release that will have it fixed



On Tue, 10 Jan 2023 13:36:02 +0100 Faustin Lammler <faustin at fala.red> wrote:
> Hi,
> first of all, thank you all for the excellent (and detailed) report!
>
> I don't see anything that could be related with Debian packaging of
> MariaDB and so I suggest you check directly upstream.
>
> I have searched into https://jira.mariadb.org and the closest report
> that I can come with is https://jira.mariadb.org/browse/MDEV-29988. I do
> not forward this bug report to it because I am not sure that this is the
> same problem.
>
> There is also https://jira.mariadb.org/browse/MDEV-29097 that may give
> some ideas on how to find a workaround until the next release happen.
>
> Cheers!
>
> --
> Faustin
> GPG: F652 BCD1 1AA8 8975 F010 48A5 390A 2F27 832A 5C79

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