Horton

Re: unlogged tables vs. GIST

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, pgsql-hackers@postgresql.org
Date: 2010-12-17T21:17:56Z
Lists: pgsql-hackers

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  1. The GiST scan algorithm uses LSNs to detect concurrent pages splits, but

[ hit send too soon ... ]

Robert Haas <robertmhaas@gmail.com> writes:
> Since these bits will only be set/cleared when the buffer mapping is
> changed, can we examine this bit without taking the spinlock?

Only if you're willing for the result to be unreliable.  In the
case of the xlog flush bit, I don't believe an extra locking cycle
should be necessary anyway, as you surely had the lock when you 
found the page to be dirty in the first place.  You could grab the
bit then.  I'm not sure where you envision checking the other bit,
but I doubt it can be all that far removed from a lock acquisition.

			regards, tom lane