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2017-06-13T05:37:43.075604

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VirtQueryOptDiagnostic

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%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]]

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