[Zope-dev] Serving big files thru zope?

[Dieter Maurer]

Jeremy Hylton wrote at 2004-3-1 14:01 -0500:
> ...
>It really would be good to get to the bottom of the bad ZEO performance
>for loading an object the first time.  I won't have time to do it until
>after the ZODB 3.3 release, but I think it's a worthwhile effort to
>understand what ZEO is doing.

I instrumented "ClientStorage" to get precise timings
for ZEO operations. The obtained times are not bad:

    When the data file was not yet in the operating system's
    cache, loading an object took between 3 to 30 ms
    with very high variance.

    After the relevant parts of the data file have been cached
    by the OS, time was between 1 to 3 ms per object, almost
    independent from object size.

    I obsevered loading of about 1.600 objects between several
    hundred bytes and several kilobytes in size
    mostly index data for a ZCatalog "FieldIndex".

    I had disabled both the ZODB cache as well as
    the ZEO client cache for my measurement.

    ZEO client and server have been on the same machine (local
    communication)

I interpreted these observations in the following way:

  *  time is dominated by the disc access

  *  time is largely independent of the object size (if
     the object is in the OS disc cache)

  *  ZEO overhead is about 1 to 3 ms per object.

-- 
Dieter