On 2014-09-02 04:34, Hugh Williams wrote:
> Hi Bart,
>
> It would be interesting to see the compiler statistics for running this
> sequence of queries which can be obtained by running the command:
>
> exp_stat_to_file ('stat.dv');
>
> as detailed at:
>
>
> http://virtuoso.openlinksw.com/dataspace/doc/dav/wiki/Main/VirtQueryOptDiagnostic
>
> which should show how the query plan changes when the 100th executions are
> occurring and the query is taking seconds to complete.
>
> If you provide the exported "stats.dv" file this can be imported into a local
> Virtuoso instance for analysis by development ...
Hello Hugh,
Sorry for the late reply, but we had some problems with our machines.
I tried to export the statistics with
exp_stat_to_file ('stat.dv');
but that did not work:
SQL> exp_stat_to_file('stat.dv');
Connected to OpenLink Virtuoso
Driver: 07.10.3209 OpenLink Virtuoso ODBC Driver
*** Error 42001: [Virtuoso Driver][Virtuoso Server]SR185: Undefined
procedure DB.DBA.exp_stat_to_file.
at line 1 of Top-Level:
exp_stat_to_file('stat.dv')
My version of Virtuoso is
Virtuoso Open Source Edition (Column Store) (multi threaded)
Version 7.1.1-dev.3209-pthreads as of May 27 2014
Compiled for Linux (x86_64-unknown-linux-gnu)
So I used the command
string_to_file ('stat.dv', serialize(stat_export()), -2);
to export the statistics and that worked. The resulting stat.dv file
can be downloaded from
https://dl.dropboxusercontent.com/u/32340538/stat.dv
The graph with the query timings is online at
https://dl.dropboxusercontent.com/u/32340538/repeattest_with_union_b.png
The timing data itself is online at
https://dl.dropboxusercontent.com/u/32340538/repeattest_with_union_b.dat
The experiment was the following: repeat a SPARQL query 1000 times (by
sending 1000 HTTP curl requests containing a certain SPARQL query to
Virtuoso) and time its execution (using time_total from curl). As you
can see, most of the time the query takes about 1 second to execute, but
about every 100 query executions it takes much more: 4 to 8 seconds.
I am particularly interested in an explanation for this behavior. Why
do we see these 'peaks' of execution times ranging from 4 to 8 seconds?
Is Virtuoso itself causing this, or could there be an other 'external'
factor that is causing this? If there are other things I can test or
monitor to find out, or you need more information, please let me know.
Kind regards,
Bart
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