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From "Tobias Bocanegra" <tobias.bocane...@day.com>
Subject Re: Threading and Query Performance
Date Tue, 13 Mar 2007 19:32:30 GMT
well, from a first glance: the more threads you add, the faster the
queries are until you reach the number of processors. if you expect
linear improvement - that does not work, since the actual 'searching'
is synchronized (marcel, correct me if i'm saying something wrong
here).
when you add more ad more threads, the synchronization and scheduling
overhead gets bigger and you loose again overall speed.

what you must ask yourself: is '~350ms' per query fast enough for my
application? how do my queries look like? can i optimize on the query
or data structure?

regards, toby

On 3/12/07, David Johnson <dbjohnson.e@gmail.com> wrote:
> This is related to two ongoing list threads - one on synchronization and the
> other on query performance.
>
> As I have mentioned in previous posts, I have been running a variety of
> query tests.  I am using a suite of 100 queries and running them against
> Jackrabbit in several different threading scenarios - i.e., I change the #
> of threads used to run sub-sets of the 100 queries.  To be clear - if I run
> a single thread case, it will run all 100 queries, one after the other.  If
> I run 2 threads - one thread will run 50 queries, while the other thread
> will run the other 50 queries.  In all cases, the 100 queries are the same,
> the only thing that changes is the number of threads used to run them.
> Also, in all tests, the repository is read only - nothing is making any
> writes to the repository.
>
> Here are some results:
>
> 1 thread: 100 queries in 41139 ms
> 2 threads: 50 queries in 37828 ms, 50 queries in 38622 ms - total time for
> all threads to complete 38960 ms
> 4 threads: 25 queries in 25895 ms, 25 queries in 28034 ms, 25 queries in
> 32335 ms, 25 queries in 32391 ms - total time 32801 ms
> 10 threads: 10 queries in 18733 ms, 10 queries in 19894 ms, ... , 10 queries
> in 33798 ms, 10 queries in 34924 ms - total time 35286 ms
> 25 threads: 4 queries in 2413 ms, 4 queries in 11725 ms, 4 queries in 18294
> ms, ... , 4 queries in 36059 ms, 4 queries in 36222 ms
>
> Some details on the box that I am running these tests on: it is a dual Xeon
> running Linux - /proc/cpuinfo shows 4 processors, so I am assuming it is a
> dual core.  I am running Jackrabbit 1.2.3 with the Bundle Persistence
> Manager.
>
> I am not sure what the numbers above are really saying, although they don't
> really look right :-)  We have a multi-user use case - large web site with
> many ongoing reads, occasional writes.  I am using the multiple threads to
> "test" multiple users.  I am hoping that the developers with more
> understanding of the internals can explain what's going on above.
>
> I am wondering if I am hitting the synchronization issue that is being
> discussed in other posts?  Thoughts?
>
> -Dave
>


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Tobias Bocanegra, Day Management AG, Barfuesserplatz 6, CH - 4001 Basel
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