database - Do Virtualized systems effect Explain Plans? -



database - Do Virtualized systems effect Explain Plans? -

i'm having unusual , different results explain plans on postgresql. postgresql server installed on vmware machine , when executing several explain plans given sql query, different results returned. seems me hardware virtualization may provide "erroneous" info postgresql server returns "anormal , random" costs measurements. right or there other explanation surprising , unusual results?

in case, if know any, i'd appreciate helpful docs.

vacuum should regular part of database operations. it's not source of problem, though.

we recommend active production databases vacuumed (at to the lowest degree nightly), in order remove dead rows. after adding or deleting big number of rows, might thought issue vacuum analyze command affected table. update scheme catalogs results of recent changes, , allow postgresql query planner create improve choices in planning queries.

the total alternative not recommended routine use, might useful in special cases. illustration when have deleted or updated of rows in table , table physically shrink occupy less disk space , allow faster table scans. vacuum total shrink table more plain vacuum would.

since got different costs on consecutive executions, 1 under vmware , 1 without, no database changes, i'd virtualization having effect. i'm pretty sure virtual machine appear have less ram straight hardware, don't have way test that, or test effect on query optimizer right now.

database postgresql virtualization vmware explain-plan

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