Horton

Re: Replication slot stats misgivings

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Amit Kapila <amit.kapila16@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Date: 2021-03-22T04:25:16Z
Lists: pgsql-hackers 
On Sat, Mar 20, 2021 at 3:52 AM Andres Freund <andres@anarazel.de> wrote:
>
> - If max_replication_slots was lowered between a restart,
>   pgstat_read_statfile() will happily write beyond the end of
>   replSlotStats.

I think we cannot restart the server after lowering
max_replication_slots to a value less than the number of replication
slots actually created on the server. No?

>
> - pgstat_reset_replslot_counter() acquires ReplicationSlotControlLock. I
>   think pgstat.c has absolutely no business doing things on that level.

Agreed.

>
> - PgStat_ReplSlotStats etc use slotname[NAMEDATALEN]. Why not just NameData?

That's because we followed other definitions in pgstat.h that use
char[NAMEDATALEN]. I'm okay with using NameData.

>
> - pgstat_report_replslot() already has a lot of stats parameters, it
>   seems likely that we'll get more. Seems like we should just use a
>   struct of stats updates.

Agreed.

Regards,

-- 
Masahiko Sawada
EDB:  https://www.enterprisedb.com/

Commits

  1. Doc: Update logical decoding stats information.

  2. Fix tests for replication slots stats.

  3. Update replication statistics after every stream/spill.

  4. Fix the computation of slot stats for 'total_bytes'.

  5. Another try to fix the test case added by commit f5fc2f5b23.

  6. Use HTAB for replication slot statistics.

  7. Fix test case added by commit f5fc2f5b23.

  8. Add information of total data processed to replication slot stats.

  9. Use NameData datatype for slotname in stats.