Relation stats: Call pg_stat_get_* directly instead of using system views #512
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…iews Due to the way how pg_stat_all_tables and pg_statio_all_tables are defined, its significantly more expensive to query through the views when a table filter is in place, since all the data gets pulled, only for the filter to be applied afterwards. Instead, call the underlying pg_stat_get* functions directly, which has the same effect as querying the views (as they are simple views without any security barrier), and shows a major speedup in cases where a large portion of tables is filtered out. This also should provide a minor speedup in regular operations, even with no table filter in place.
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For the record, this rewrite of the query did not perform faster for the customer for whom this was a problem (we suspect they had more general I/O issues). Is this still worth doing? |
Maybe? I haven't identified a downside to this approach, and it does save a few cycles for all cases, and more so when a table filter is active (even if its not necessarily a big performance impact for regular hardware). |
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Yeah, makes sense. |
msakrejda
approved these changes
Mar 21, 2024
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Due to the way how pg_stat_all_tables and pg_statio_all_tables are defined, its significantly more expensive to query through the views when a table filter is in place, since all the data gets pulled, only for the filter to be applied afterwards.
Instead, call the underlying pg_stat_get* functions directly, which has the same effect as querying the views (as they are simple views without any security barrier), and shows a major speedup in cases where a large portion of tables is filtered out. This also should provide a minor speedup in regular operations, even with no table filter in place.