ZEO cache best practices, was Re: [ZODB-Dev] ZEO 3.2 (Zope 2.7)->3.6 (Zope 2.9) upgrading: Much slower startup due to cache filecreation

[Pascal Peregrina]

About the whole cache being verified every time an instance is restarted:
This might indicate that the ZEO invalidation queue size is too small.
So something useful to test is to increase the invalidation-queue-size param in zeo.conf (<zeo></zeo> section).
I think default size is 100, and we solved our Zope slow startup issues by increasing to 1000. Note that the ZEO instance will consume more memory to keep this information.

Pascal

-----Message d'origine-----
De : zodb-dev-bounces+pperegrina=lastminute.com at zope.org [mailto:zodb-dev-bounces+pperegrina=lastminute.com at zope.org] De la part de Jim Fulton
Envoyé : mercredi 19 avril 2006 12:17
À : Tim Peters
Cc : Paul Winkler; zodb-dev at zope.org
Objet : Re: ZEO cache best practices, was Re: [ZODB-Dev] ZEO 3.2 (Zope 2.7)->3.6 (Zope 2.9) upgrading: Much slower startup due to cache filecreation

Tim Peters wrote:
> [Paul Winkler]
> 
>>Heh. Well, I had a site that under some usage patterns would
>>occasionally slow to a crawl with cache flips every few minutes.  That
>>was with the old default 20 MB cache size.  I think I left it at
>>500 MB or so and that site's been fine since. But the performance
>>demands were pretty low.
> 
> 
> Yes, 20MB is _very_ small.  It may have seemed conservatively safe 10
> years ago when disks were much smaller, but now it's ludicrously
> small.
> 
> OTOH, the larger the ZEO cache file, the longer it may take startup or
> reconnection cache verification to complete, so there's always some
> reason not to do the obvious thing <0.3 wink>.

This is only a problem if:

1. a persistent cache is used or

2. the client gets disconnected from the server, without
    restarting, long enough for the server to commit enough
    transactions for the server to be able to do enough quick
    verification.

We seem to have a lot of problems with persistent caches for
some reason, so I tend to recommend against their use.  I'm
not sure what's going on there.  I still find them useful in
situations in which the connection to the server is slow.

the second case should be rare.

I would definately error in the direction of using a
larger cache

Jim

-- 
Jim Fulton           mailto:jim at zope.com       Python Powered!
CTO                  (540) 361-1714            http://www.python.org
Zope Corporation     http://www.zope.com       http://www.zope.org
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