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: 2010-12-17T20:15:16Z
Lists: pgsql-hackers

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

Robert Haas <robertmhaas@gmail.com> writes:
> On Fri, Dec 17, 2010 at 3:03 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Yeah. I think that BM_UNLOGGED might be a poor choice for the flag name,
>> just because it overstates what the bufmgr needs to assume.

> I was actually thinking of adding BM_UNLOGGED even before this
> discussion, because that would allow unlogged buffers to be excluded
> from non-shutdown checkpoints.  We could add two flags with different
> semantics that take on, under present rules, the same value, but I'd
> be disinclined to burn the extra bit without a concrete need.

bufmgr is currently using eight bits out of a 16-bit flag field, and
IIRC at least five of those have been there since the beginning.  So our
accretion rate is something like one bit every four years.  I think not
being willing to use two bits to describe two unrelated behaviors is
penny-wise and pound-foolish --- bufmgr is already complicated enough,
let's not add useless barriers to readability.

			regards, tom lane