[ZODB-Dev] ZEO 2 : cache twiddling

[Toby Dickenson]

On Friday 22 November 2002 10:20 am, Chris Withers wrote:
> Toby Dickenson wrote:
> >>Do I want a persistent cache?
> >
> > You probably only *need* a persistent cache if there is a slow networ=
k
> > between your ZEO clients and servers.
>
> Can you explain a little further? Then network between the clients and
> servers is a LAN, so I wouldn't say it's slow,

Thats fast enough that you dont *need* one.

There are certainly some disadvantages to having one:
* extra admin complexity (a little, anyway)
* one more thing to go wrong.
* the cache has to be validated at client startup. This causes:
  * extra startup latency=20
  * a significant server load burst

Those last points could be eliminated if ZEO validated the cached objects=
 when=20
they were accessed, rather than eagerly at startup. I think there was a=20
proposal to change this....

> but I'm curious as to why
> the persistency of the cache is related to the network speed.

The cache can reduce the number of bytes sent over the network immediatel=
y=20
after startup (until the volatile caches have been filled).

If your ZEO clients connect to the server over a modem (for example), the=
n=20
these bandwidth savings are much more attractive.