| Attributes | Values |
|---|
| type
| |
| Date Created
| |
| Date Modified
| |
| label
| |
| maker
| |
| Title
| |
| isDescribedUsing
| |
| has creator
| |
| content
| - %META:TOPICPARENT{name="VirtTipsAndTricksGuide"}%
---+ Virtuoso Diagnostics for Query Optimization
Queries involving a large number of possible plans may run out of memory during optimization. There
are a number of settings that influence query optimization memory utilization.
These are set in the <code>virtuoso.ini</code> file, or can be altered on a running system with the
<b><code>[[http://docs.openlinksw.com/virtuoso/fn_dbf_set.html][__dbf_set()]]</code></b> function.
| *INI section* | *INI param name* | *default value* | *__dbf_set flag_name* | *__dbf_set flag_name description* |
| Parameters | <code><nowiki>MaxMemPoolSize</nowiki></code> | <code>200000000</code> | <code><nowiki>sqlo_max_mp_size</nowiki></code> | The <b><code><nowiki>sqlo_max_mp_size</nowiki></code></b> is a size limit in bytes for transient memory consumption. Increasing this may help. The <b><code><nowiki>sqlo_max_mp_size</nowiki></code> </b> should be over 10M; increasing this over 100M is seldom useful but can be tried. |
| Parameters | <code><nowiki>MaxOptimizeLayouts</nowiki></code> | <code>1000</code> | <code><nowiki>sqlo_max_layouts</nowiki></code> | Decreasing <b><code><nowiki>sqlo_max_layouts</nowiki></code></b> will reduce the number of plans tried, hence save memory. Reasonable values for <b><code><nowiki>sqlo_max_layouts</nowiki></code></b> are 0 for no limit, or somewhere in excess of 500. |
| Parameters | <code><nowiki>StopCompilerWhenXOverRunTime</nowiki></code> | <code>0</code> | <code><nowiki>sqlo_compiler_exceeds_run_factor</nowiki></code> | Setting <b><code><nowiki>sqlo_compiler_exceeds_run_factor</nowiki></code></b> to 1 will stop opttimization once the best plan is expected to take less time than the amount of time spent optimizing so far. |
| Flags | <code><nowiki>enable_joins_only</nowiki></code> | <code>1</code> | <code><nowiki>enable_joins_only</nowiki></code> | Setting <b><code><nowiki>enable_joins_only</nowiki></code></b> will cause the optimizer to only consider next plan candidates that are connected by a join to the existing partial plan. In other words, no [[http://dbpedia.org/resource/Cartesian_product][Cartesian products]] will be considered. This may save some space and time. <b>Note:</b> This option is now the default with <b><code><nowiki>3215</nowiki></code></b>+ builds and there are no known cases when it should be set to 0.|
When reporting issues with query optimization, it will be useful to include statistics from the database
in order to facilitate reproducing the effect. The <b><code>[[http://docs.openlinksw.com/virtuoso/fn_stat_export.html][stat_export()]]</code></b>
function produces a statistics summary that can be read back into another database with the
<b><code>[[http://docs.openlinksw.com/virtuoso/fn_stat_import.html][stat_import()]]</code></b> function.
* To export statistics:
<verbatim>
string_to_file ('stat.dv', serialize(stat_export()), -2);
or
exp_stat_to_file ('stat.dv'); which does not have 10MB file size limit
</verbatim>
* To load exported statistics into a database:
<verbatim>
stat_import (deserialize (file_to_string ('stat.dv')));
</verbatim>
When exporting statistics as part of bug reporting, make sure to run the queries exhibiting the problem before exporting the stats. The queries drive statistics gathering.
---++Related
* [[VirtTipsAndTricksGuide][Virtuoso Tips and Tricks Collection]]
* [[http://docs.openlinksw.com/virtuoso/sqloptimizer.html][Virtuoso SQL Optimization]]
|
| id
| - c8b4135cd6fa24198c53115c4063e405
|
| link
| |
| has container
| |
| http://rdfs.org/si...ices#has_services
| |
| atom:title
| |
| links to
| |
| atom:source
| |
| atom:author
| |
| atom:published
| |
| atom:updated
| |
| topic
| |
| is made
of | |
| is container of
of | |
| is link
of | |
| is http://rdfs.org/si...vices#services_of
of | |
| is links to
of | |
| is creator of
of | |
| is atom:entry
of | |
| is atom:contains
of | |
![[RDF Data]](/fct/images/sw-rdf-blue.png)
![[cxml]](/fct/images/cxml_doc.png)
![[csv]](/fct/images/csv_doc.png)
![[text]](/fct/images/ntriples_doc.png)
![[turtle]](/fct/images/n3turtle_doc.png)
![[ld+json]](/fct/images/jsonld_doc.png)
![[rdf+json]](/fct/images/json_doc.png)
![[rdf+xml]](/fct/images/xml_doc.png)
![[atom+xml]](/fct/images/atom_doc.png)
![[html]](/fct/images/html_doc.png)