pgsql: Initialize GIN metapage correctly when replaying metapage-update

Initialize GIN metapage correctly when replaying metapage-update WAL record.

I broke this with my WAL format refactoring patch. Before that, the metapage
was read from disk, and modified in-place regardless of the LSN. That was
always a bit silly, as there's no need to read the old page version from
disk disk when we're overwriting it anyway. So that was changed in 9.5, but
I failed to add a GinInitPage call to initialize the page-headers correctly.
Usually you wouldn't notice, because the metapage is already in the page
cache and is not zeroed.

One way to reproduce this is to perform a VACUUM on an already vacuumed
table (so that the vacuum has no real work to do), immediately after a
checkpoint, and then perform an immediate shutdown. After recovery, the
page headers of the metapage will be incorrectly all-zeroes.

Reported by Jeff Janes

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/47fe4d25d57c81b9d7b2ac88783a12ee487db220

Modified Files
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src/backend/access/gin/ginxlog.c | 1 +
1 file changed, 1 insertion(+)