pgstattuple: fix free space calculation
Frédéric Yhuel <frederic.yhuel@dalibo.com>
From: Frédéric Yhuel <frederic.yhuel@dalibo.com>
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-08-22T08:10:53Z
Lists: pgsql-hackers
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Consistently use PageGetExactFreeSpace() in pgstattuple.
- de239d01e7cc 18.0 landed
Attachments
- 0001-pgstattuple-use-PageGetExactFreeSpace.patch (text/x-patch) patch 0001
Hello,
I think that pgstattuple should use PageGetExactFreeSpace() instead of
PageGetHeapFreeSpace() or PageGetFreeSpace(). The latter two compute the
free space minus the space of a line pointer. They are used like this in
the rest of the code (heapam.c):
pagefree = PageGetHeapFreeSpace(page);
if (newtupsize > pagefree) { we need a another page for the tuple }
... so it makes sense to take the line pointer into account in this context.
But it in the pgstattuple context, I think we want the exact free space.
I have attached a patch.
Best regards,
Frédéric