pgsql: Save a few cycles during nbtree VACUUM.

Save a few cycles during nbtree VACUUM.

Avoid calling RelationGetNumberOfBlocks() unnecessarily in the common
case where there are no deleted but not yet recycled pages to recycle
during a cleanup-only nbtree VACUUM operation.

Follow-up to commit e5d8a999, which (among other things) taught the
"skip full scan" nbtree VACUUM mechanism to only trigger a full index
scan when the absolute number of deleted pages in the index is
considered excessive.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7bb97211a5589265f3f88183ae9353639ab184c6

Modified Files
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src/backend/access/nbtree/nbtree.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)