This is V4 patch to improve file read during startup for review.
Basic algorithm is same as V3 but works with Gregory's fadvise patch.
http://archives.postgresql.org/pgsql-hackers/2009-01/msg00026.php
This patc also include additional patch for posix_fadvise to skip
prefetch of pages which does not exist.
We still need a patch to work this with syncronous replication, which
will be posted by the end of this week.
Regards;
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Koichi Suzuki