Re: unlogged tables vs. GIST

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