Comments on: Execution Plan Hash Value in SQL Trace Files http://antognini.ch/2009/01/execution-plan-hash-value-in-sql-trace-files/ Fri, 27 Jan 2012 07:31:12 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: Alberto Dell'Era http://antognini.ch/2009/01/execution-plan-hash-value-in-sql-trace-files/comment-page-1/#comment-339 Alberto Dell'Era Mon, 26 Jan 2009 10:19:41 +0000 http://antognini.ch/?p=65#comment-339 Milen, sure, I should have been more precise - "compilation" as in "production of the SQL Engine 'instructions', i.e. the 'row source operations' that together compose 'the plan' " - the "optimization". It was meant as an observation: the reason why the "plh" value of the PARSE line is not reliable is because (at least when bind variables are used) at PARSE time there is no plan associated (or a possibly "old" plan is associated); only at EXEC time the plan is (re)calculated. Milen,
sure, I should have been more precise – “compilation” as in “production of the SQL Engine ‘instructions’, i.e. the ‘row source operations’ that together compose ‘the plan’ ” – the “optimization”.

It was meant as an observation: the reason why the “plh” value of the PARSE line is not reliable is because (at least when bind variables are used) at PARSE time there is no plan associated (or a possibly “old” plan is associated); only at EXEC time the plan is (re)calculated.

]]> By: Milen Kulev http://antognini.ch/2009/01/execution-plan-hash-value-in-sql-trace-files/comment-page-1/#comment-338 Milen Kulev Sun, 25 Jan 2009 16:28:00 +0000 http://antognini.ch/?p=65#comment-338 Alberto, not only the actual compilation, but under some conditions the re-optimization will be postponed to the EXEC phase. See ML 199273.1. An excerpt from this ML: " . Certain phases may be repositioned dependant on the query submitted. Oracle may combine steps or defer them to a later stage. For example, if bind variable 'peeking' is in operation, then the optimizer needs to use the first 'bound' value to determine the execution plan for the query. This means that optimization will actually occur in the EXECUTE phase as this is the first time that any bind variable values are available. " Best Regards. Milen Alberto,
not only the actual compilation, but under some conditions the re-optimization will be postponed to the EXEC phase.
See ML 199273.1. An excerpt from this ML:
”
. Certain phases may be repositioned dependant on the query submitted. Oracle may combine steps or defer them to a later stage. For example, if bind variable ‘peeking’ is in operation, then the optimizer needs to use the first ‘bound’ value to determine the execution plan for the query. This means that optimization will actually occur in the EXECUTE phase as this is the first time that any bind variable values are available.
”

Best Regards. Milen

]]> By: Alberto Dell'Era http://antognini.ch/2009/01/execution-plan-hash-value-in-sql-trace-files/comment-page-1/#comment-306 Alberto Dell'Era Sun, 18 Jan 2009 23:13:35 +0000 http://antognini.ch/?p=65#comment-306 This shows, of course, that the actual compilation of the SQL statement happens during the EXECution, not the PARSing - at least for statements using bind variables :) This shows, of course, that the actual compilation of the SQL statement happens during the EXECution, not the PARSing – at least for statements using bind variables :)

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