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Don Burleson Blog 









plsql_optimize_level parameter

Oracle Database Tips by Donald Burleson

This test indicates that the default setting for plsql_optimize_level in Oracle 10g (default plsql_optimize_level=2), can make a 10x speed difference for

"I run the script for it takes 3 seconds, does ~30000 LIOs/sec/CPU via 40300 LIOs.

I run the script for it takes .25 seconds"

This result may be due to the automatic bulking of fetches in PL/SQL, as noted by the plsql_optimize_level parameter.  Steve Feuerstein notes the values for plsql_optimize_level below. 


       2 Most aggressive, maximum possible code transformations, biggest impact on compile time. [default]

       1 Smaller scale change, less impact on compile times

       0 Pre-10g compilation without optimization


Setting plsql_optimize_level=2 (the default) will often replace cursor for loops (CFL) to the faster bulk collect.  Feuerstein offers the following advice on this PL/SQL transformation with plsql_optimize_level:

"If you want to do complex processing on each row as it is queried - and possibly halt further fetching.

You are retrieving many rows and cannot afford to use up the memory (large numbers of users).

Otherwise, moving to BULK COLLECT is a smart move"



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