Dieter Maurer wrote:
We do not yet precisely the cause of our commit contentions.


Hard to tell what'll make them better then. ;)

Almost surely there are several causes that all can lead to contention.

We already found:

  *  client side causes (while the client helds to commit lock)
- garbage collections (which can block a client in the order of
      10 to 20 s)

Interesting. Perhaps someone might enjoy investigating turning off garbage collection during commits.

    - NFS operations (which can take up to 27 s in our setup -- for
      still unknown reasons)

Not much ZODB can do about that. ;)

    - invalidation processing, espicially ZEO ClientCache processing

Interesting. Not knowing much about how invalidations are handled, I'm curious where the slow-down is. Do you have any more detail?

  *  server side causes

    - commit lock hold during copy phase of pack

    - IO trashing during the reachability analysis in pack

The new pack code should help quite a bit with the above (if you're saying what I think you're saying).

    - non deterministic server side IO anomalities
      (IO suddently takes several times longer than usual -- for still
      unknown reasons)

Curious.
--
Benji York
Senior Software Engineer
Zope Corporation
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