From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Noah Misch <noah(at)leadboat(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: pgsql: Fix a couple of bugs in MultiXactId freezing |
Date: | 2013-12-13 16:39:20 |
Message-ID: | 20131213163920.GD12902@eldon.alvh.no-ip.org |
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Alvaro Herrera wrote:
> So I think this is the only remaining issue to make this patch
> committable (I will address the other points in Andres' email.) Since
> there has been no other feedback on this thread, Andres and I discussed
> the cache issue a bit over IM and we seem to agree that a patch to
> revamp the cache should be a fairly localized change that could be
> applied on both 9.3 and master, separately from this fix. Doing cache
> deletion seems more invasive, and not provide better performance anyway.
Here's cache code with LRU superpowers (ahem.)
I settled on 256 as number of entries because it's in the same ballpark
as MaxHeapTuplesPerPage which seems a reasonable guideline to follow.
I considered the idea of avoiding palloc/pfree for cache entries
entirely, instead storing them in a static array which is referenced
from the dlist; unfortunately that doesn't work because each cache entry
is variable size, depending on number of members. We could try to work
around that and allocate a large shared array for members, but that
starts to smell of over-engineering, so I punted.
I was going to 'perf' this, but then found out that I need to compile my
own linux-tools package for a home-compiled kernel ATM.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
Attachment | Content-Type | Size |
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revamp-multixact-cache.patch | text/x-diff | 5.2 KB |
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