Timing of pgstats updates

"David Parker" <dparker(at)tazznetworks(dot)com> writes:
> What I think is happening with the missing pg_statistic entries:
> The install of our application involves a lot of data importing (via
> JDBC) in one large transaction, which can take up to 30 minutes. (I
> realize I left out this key piece of info in my original post...)

> The pg_autovacuum logic is relying on data from pg_stat_all_tables to
> make the decision about running analyze. As far as I can tell, the data
> in this view gets updated outside of the transaction, because I saw the
> numbers growing while I was importing. I saw pg_autovacuum log messages
> for running analyze on several tables, but no statistics data showed up
> for these, I assume because the actual data in the table wasn't yet
> visible to pg_autovacuum because the import transaction had not finished
> yet.

> When the import finished, not all of the tables affected by the import
> were re-visited because they had not bumped up over the threshold again,
> even though the analyze run for those tables had not generated any stats
> because of the still-open transaction.

Bingo. The per-table activity stats are sent to the collector whenever
the backend waits for a client command. Given a moderately long
transaction block doing updates, it's not hard at all to imagine that
autovacuum would kick off vacuum and/or analyze while the updating
transaction is still in progress. The resulting operation is of course
a waste of time.

It'd be trivial to adjust postgres.c so that per-table stats are
only transmitted when we exit the transaction (basically move the
pgstat_report_tabstat call down a couple lines so it's not called if
IsTransactionOrTransactionBlock).

This seems like a good change to me. Does anyone not like it?

regards, tom lane