pgsql: Improve handling of dead tuples in hash indexes.

Improve handling of dead tuples in hash indexes.

When squeezing a bucket during vacuum, it's not necessary to retain
any tuples already marked as dead, so ignore them when deciding which
tuples must be moved in order to empty a bucket page. Similarly, when
splitting a bucket, relocating dead tuples to the new bucket is a
waste of effort; instead, just ignore them.

Amit Kapila, reviewed by me. Testing help provided by Ashutosh
Sharma.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/f0e72a25b05d4c29d0102fa0b892782ff193a00e

Modified Files
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src/backend/access/hash/hashovfl.c | 4 ++++
src/backend/access/hash/hashpage.c | 4 ++++
2 files changed, 8 insertions(+)