|From:||Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>|
|To:||David Gould <daveg(at)sonic(dot)net>|
|Cc:||Alexander Kuzmenkov <a(dot)kuzmenkov(at)postgrespro(dot)ru>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Alina Alexeeva <alexeeva(at)adobe(dot)com>, Ullas Lakkur Raghavendra <lakkurra(at)adobe(dot)com>|
|Subject:||Re: [patch] BUG #15005: ANALYZE can make pg_class.reltuples inaccurate.|
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> Maybe this type of situation is an argument for trusting an ANALYZE-based
> estimate more than the VACUUM-based estimate. I remain uncomfortable with
> that in cases where VACUUM looked at much more of the table than ANALYZE
> did, though. Maybe we need some heuristic based on the number of pages
> actually visited by each pass?
I looked into doing something like that. It's possible, but it's fairly
invasive; there's no clean way to compare those page counts without
altering the API of acquire_sample_rows() to pass back the number of pages
it visited. That would mean a change in FDW-visible APIs. We could do
that, but I don't want to insist on it when there's nothing backing it up
except a fear that *maybe* ANALYZE's estimate will be wrong often enough
to worry about.
So at this point I'm prepared to go forward with your patch, though not
to risk back-patching it. Field experience will tell us if we need to
do more. I propose the attached cosmetic refactoring, though.
regards, tom lane
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