From: | "Simon Riggs" <simon(at)2ndquadrant(dot)com> |
---|---|
To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "Jim C(dot) Nasby" <jim(at)nasby(dot)net>, "ITAGAKI Takahiro" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Dead Space Map version 2 |
Date: | 2007-02-27 08:16:54 |
Message-ID: | 1172564214.3760.547.camel@silverbirch.site |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers pgsql-patches pgsql-performance |
On Tue, 2007-02-27 at 00:55 -0500, Tom Lane wrote:
> "Jim C. Nasby" <jim(at)nasby(dot)net> writes:
> > Yes, DSM would make FSM recovery more important, but I thought it was
> > recoverable now? Or is that only on a clean shutdown?
>
> Currently we throw away FSM during any non-clean restart. This is
> probably overkill but I'm quite unclear what would be a safe
> alternative.
>
> > I suspect we don't need perfect recoverability...
>
> The main problem with the levels proposed by Takahiro-san is that any
> transition from FROZEN to not-FROZEN *must* be exactly recovered,
> because vacuum will never visit an allegedly frozen page at all. This
> appears to require WAL-logging DSM state changes, which is a pretty
> serious performance hit. I'd be happier if the DSM content could be
> treated as just a hint. I think that means not trusting it for whether
> a page is frozen to the extent of not needing vacuum even for
> wraparound.
Agreed.
> So I'm inclined to propose that there be only two states
> (hence only one DSM bit per page): page needs vacuum for space recovery,
> or not. Vacuum for XID wraparound would have to hit every page
> regardless.
I'm inclined to think: this close to deadline it would be more robust to
go with the simpler option. So, agreed to the one bit per page.
We can revisit the 2 bits/page idea easily for later releases. If the
DSM is non-transactional, upgrading to a new format in the future should
be very easy.
--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com
From | Date | Subject | |
---|---|---|---|
Next Message | ITAGAKI Takahiro | 2007-02-27 08:38:39 | Re: Dead Space Map version 2 |
Previous Message | Simon Riggs | 2007-02-27 08:11:37 | Re: Dead Space Map version 2 |
From | Date | Subject | |
---|---|---|---|
Next Message | ITAGAKI Takahiro | 2007-02-27 08:38:39 | Re: Dead Space Map version 2 |
Previous Message | Simon Riggs | 2007-02-27 08:11:37 | Re: Dead Space Map version 2 |
From | Date | Subject | |
---|---|---|---|
Next Message | Peter Kovacs | 2007-02-27 08:27:52 | Re: Two hard drives --- what to do with them? |
Previous Message | Simon Riggs | 2007-02-27 08:11:37 | Re: Dead Space Map version 2 |