maria-developers team mailing list archive

[Alexey Botchkov <holyfoot@xxxxxxxxxxxx>]

Hi, Mattias, guys!

While investigating the crash, i'd like to discuss that

> it seems to close partitions whenever it
> is not used in a statement (i.e. require it to be reopened in the next
> statement that would use another partition

Yes, it does that, handling statements with the specified 'PARTITION' 
option.
The patch supposed to solve the problem when there are too many 
partitions opened,
so i think it must close the unused partitions sometime.
No, it doesn't have to happen that often. I planned to check the 
table_open_cache
variable before the forced close. But decided not to do that initially - 
as it simplified testing,
and i thought if someone uses the PARTITION option, he would stick to 
using this partition
anyway. And  i forgot about that issue.


Best regards.
HF



13.04.2018 19:07, Mattias Jonsson wrote:
> Hi MariaDB Devs,
>
> I tried to evaluate spider engine and found an issue where it crashes,
> most likely due to MDEV-11084 (Stacktrace and reproducible test case
> attached).
>
> That also leads me to wonder about the performance for partitioned
> tables after MDEV-11084, when it seems to close partitions whenever it
> is not used in a statement (i.e. require it to be reopened in the next
> statement that would use another partition, effectively not using the
> open table cache).
>
> I cannot see anything mentioned in the final commit message hinting on
> that it closes partitions not used in the current query, but in the
> previous patches it was mentioned without any reason.
>
> Why does it close the already opened partitions?
> https://github.com/MariaDB/server/blob/10.3/sql/ha_partition.cc#L8365
>
> I would not mind opening the partitions only when they are to be used
> (even though there are engines that need to be tested more), but
> closing them makes no sense to me performance wise. Also notice that
> the partitions first will be put back into the open table cache and
> then on the next query the non-used partitions will be closed and the
> needed ones be (re)-opened.
>
> Regards
> Mattias Jonsson