On Wed, 14 May 2008, Kevin Grittner wrote:
If this is the first time that the rows are being read since they were inserted (or since the database was loaded, including from backup), it may be rewriting the rows to set hint bits, which can make subsequent access faster.
This is the second time this has come up recently, and I know it used to puzzle me too. This is a particularly relevant area to document better for people doing benchmarking. As close I've found to a useful commentary on this subject is the thread at http://archives.postgresql.org/pgsql-patches/2005-07/msg00390.php
I still don't completely understand this myself though, if I did I'd add a FAQ on it. Anyone want to lecture for a minute on the birth and care of hint bits? I'll make sure any comments here get onto the wiki.
-- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD
