Re: Powerfailure caused a reduction in INSERT performance of version 12 database.

On Mon, Aug 19, 2024 at 9:08 AM Frank Komsic <komsicf(at)shoeicanada(dot)com>
wrote:

> Hi Steve,
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> Thank you for your suggestions.
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> Steve wrote:
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> I'm far from an expert in this area but running explain it explain analyze
> seems like a useful thing to share with the group. Then I wonder if running
> vacuum analyze would be useful? Maybe the planner is doing something weird.
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> I have done a VACUUM ANALYZE and a VACUUM FULL on the questionable table
> with marginal improvement but still it seems to be slower than previously.
> I tried EXPLAIN ANALYZE and it does show it is slow for the number of
> records. REINDEXED the index with little success as well.
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> I'd also check if you lost any indexes you need during the bad day?
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> How do I check that?
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> Also being sure your system performance stats are correct - are you using
> all the cores and ram that you expect? Is the disk temporary space and swap
> performing normally?
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> Need to see and verify that… do not have historical data on the
> performance. Is there a way to get historicals or does it require a third
> party software?
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> Are other tables unaffected, somewhat affected or in the same situation as
> this table.
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> It seems other tables are fine as they do not have triggers on them. The
> data table of millions of records seems to visualize 100 k records faster
> than the table in question.
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> Currently I stopped all updates and the table visualizes in a little over
> 2 seconds. Previously while the updates were running it took 4 to 7
> seconds to visualize.
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> I'd recommend, if your environment can tolerate debugging, with
> reuploading this table's data into an identical table and see if the
> problem exists there too.
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> I am not an expert in PostgreSQL. We have lost our programmer and do not
> have afall back plan for now. I have been educating myself on the
> administration of postgresql, just this problem seems a bit unusual from
> the training I had.
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> How can I reupload the data into an identical table?
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> Also if you dump the entire database can you reload in a new server and
> replicate there?
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> Yes the ultimate way to verify. I gather it would be a pg_basebackup and
> then restore function?
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> I hope this helps,
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> Steve
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>

I am not a postgres admin expert, but if I had this issue, I'd use pg_dump
and pg_restore. I'm not familiar with pg_basebackup, but maybe it is more
robust. Basically I'd run pg_dump (iirc "-F c" will dump in custom/native
format), install the SAME version of postgres onto a machine with similar
hardware, create a new database with the same name, then run pg_restore to
get the data back into that.

Regarding your explain analyze: again I'm no expert, but I really don't
understand how a table with 2500 rows and 18 cols can take 2.5s to
enumerate.. So that remains a very mysterious thing for me. But pulling the
data to a new server/database and verifying that the same problem occurs
there seems wise.

But regarding the "width" - I believe that's a measure of all the columns
concatenated together, returned in bytes, but I could be wrong.

The fact that there is a trigger on this table is suggestive that there is
maybe a locking issue that is interfering with the search. If you can copy
the data to a new location, you can disable the trigger to verify if that's
a big part of the problem..

Steve