Re: IO related waits

On Tue, 17 Sept 2024 at 18:43, Greg Sabino Mullane <htamfids(at)gmail(dot)com>
wrote:

>
> This is a better place to optimize. Batch many rows per transaction.
> Remove unused indexes.
>
> flushing of the WAL to the disk has to happen anyway(just that it will be
>> delayed now), so can this method cause contention in the database storage
>> side if the speed in which the data gets ingested from the client is not
>> getting written to the disk , and if it can someway impact the data
>> consistency for the read queries?
>>
>
> Not quite clear what you are asking here re data consistency. The data
> will always be consistent, even if synchronous_commit is disabled. The only
> danger window is on a server crash.
>
> (Keep in mind that RDS is not Postgres, so take tuning recommendations and
> advice with a grain of salt.)
>
>
>
Thank you Greg.

Yes, our Java application was doing row by row commit and we saw that from
pg_stat_database from the column "xact_commit" which was closely the same
as the sum of tup_inserted, tup_updated, tup_deleted column. And also we
verified in pg_stats_statements the number against the "calls" column were
matching to the "rows" column for the INSERT queries, so it means also we
are inserting exactly same number of rows as the number of DB calls, so it
also suggest that we are doing row by row operations/dmls.

And we then asked the application tema to make the inserts in batches, but
still seeing those figures in these above two views are not changing much
the number "xact_commit" is staying almost same and also even the "calls"
and the "rows" column in pg_stats_statements also staying almost same. So
does it mean that the application code is somehow still doing the same row
by row processing or we are doing something wrong in the above analysis?

And another thing we noticed , even after the data load finished , even
then the "xact_commit" was keep increasing along with "tup_fetched", so
does it mean that its doing some kind of implicit commit even for the fetch
type queries which must be "select" queries i believe? Also not sure if its
expected, but here in postgres i have seen unless we put a code within
begin and end block , it's default gets committed even we just run it on
the console , it doesn't ask for a explicit commit/rollback ,so not sure if
that is someway playing a role here.

Regards
Veem

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