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List: zodb-dev
Subject: Re: [ZODB-Dev] ZODB blob support.
From: Toby Dickenson <tdickenson () devmail ! geminidataloggers ! co ! uk>
Date: 2005-03-21 13:46:03
Message-ID: 200503211346.03966.tdickenson () devmail ! geminidataloggers ! co ! uk
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On Thursday 17 March 2005 19:59, Chris McDonough wrote:
> Hi folks,
>
> In preparation for some work that will tentatively happen at the Pycon
> sprints, I've put up a very basic proposal outlining "blob" support for
> ZODB. It would help if people with a stake in ZODB had the time to
> comment on it before work starts (please comment here, as opposed to on
> the proposal itself, just so we get the widest audience).
>
> http://www.plope.com/Members/chrism/zodb_blob_proposal
Replying here to some comments in that wiki.....
| Prevent blob data from evicting "more important" data that lives in
| a ZODB or ZEO cache.
Rather than having blobs bypassing the normal caches, I think the right
solution is to have these caches using a smarter cache eviction policy.
The connection cache uses least-recently-used, and the ZEO cache uses an
approximation of lru. A better cache eviction algorithm would be aware of
different object characteristics. IMHO blobs are only one not-so-special
case. I suspect there would also be a benefit to making those tiny internal
BTree nodes particularly cache-sticky. Ive written about this a little
before: http://mail.zope.org/pipermail/zope-dev/2003-April/019418.html
| some benchmarks I ran a while ago indicated that the current Pdata
| solution for OFS.Image suffers greatly when used with ZEO
Thats not only true for blobs surely. I guess some prefetching/readahead would
help alot of ZEO benchmarks.
--
Toby Dickenson
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