Horton

Re: unlogged tables vs. GIST

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>

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From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, pgsql-hackers@postgresql.org
Date: 2010-12-17T19:19:11Z
Lists: pgsql-hackers

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

On 17.12.2010 21:07, Tom Lane wrote:
> IIUC, the problem is that the bufmgr might think that a GIST NSN is an
> LSN that should affect when to force out a dirty buffer?  What if we
> taught it the difference?  We could for example dedicate a pd_flags
> bit to marking pages whose pd_lsn isn't actually an LSN.
>
> This solution would probably imply that all pages in the shared buffer
> pool have to have a standard PageHeaderData header, not just an LSN at
> the front as is assumed now.  But that doesn't seem like a bad thing to
> me, unless maybe we were dumb enough to not use a standard page header
> in some of the secondary forks.

I'm not very fond of expanding buffer manager's knowledge of the page 
layout. How about a new flag in the buffer desc, BM_UNLOGGED? There was 
some talk about skipping flushing of unlogged tables at checkpoints, I 
think we'd need BM_UNLOGGED for that anyway. Or I guess we could hang 
that behavior on the pd_flags bit too, but it doesn't seem like the 
right place for that information.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com