Log Message:
-----------
Only skip pages marked as clean in the visibility map, if the last 32
pages were marked as clean as well. The idea is to avoid defeating OS
readahead by skipping a page here and there, and also makes it less likely
that we miss an opportunity to advance relfrozenxid, for the sake of only
a few skipped pages.
Modified Files:
--------------
pgsql/src/backend/commands:
vacuumlazy.c (r1.117 -> r1.118)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuumlazy.c?r1=1.117&r2=1.118)