pgsql: bufmgr: Return early in ScheduleBufferTagForWriteback() if fsync

bufmgr: Return early in ScheduleBufferTagForWriteback() if fsync=off

As pg_flush_data() doesn't do anything with fsync disabled, there's no point
in tracking the buffer for writeback. Arguably the better fix would be to
change pg_flush_data() to flush data even with fsync off, but that's a
behavioral change, whereas this is just a small optimization.

Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Reviewed-by: Noah Misch <noah(at)leadboat(dot)com>
Discussion: https://postgr.es/m/1f6b50a7-38ef-4d87-8246-786d39f46ab9@iki.fi

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/488f826c729bd570c36df369fa8ac90c9a5a1b46

Modified Files
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src/backend/storage/buffer/bufmgr.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)