Mauro Pagano's Blog

Little help in creating SQL Plan Baselines

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One of the main design goals behind SQLd360 is to have no installation nor “evidence” left in the database, i.e. there is no SQLd360 repository in the database while there is a SQLTXPLAIN one (this isn’t necessarily bad, it’s just a different approach).

As a consequence several little things SQLT provided are gone with SQLd360, for example few years ago (it’s been disabled by default for a while) SQLT generated a script to create a “custom” SQL Profile for the best performing plan it identified, something similar was happening for SQL Plan Baselines stored in SQL Tuning Set for quick implementation of baselines down the road.

There is a new standalone script shipped with SQLd360, sql/sqld360_create_sql_baseline.sql, that aims at providing the same functionality of SPM+STS provided by SQLT, using the idea of “no evidence left by default”.
The script is NOT executed as part of SQLd360, it can (and needs to) be manually executed at any time, which in turns means there is no need to run SQLd360 for this script to work.
The script requires three parameters:

  • SQL ID for the SQL of interest
  • Oracle Pack available in this database ([N]one, [D]iagnostic or [T]uning)
  • Plan Hash Value you wish to “freeze”

You can provide the parameters directly inline to SQL*Plus (assuming you know the PHV you want to enforce) or just enter them one by one when prompted, the script will list all the PHV it can find around (memory + history) with their performance, helping you in case you don’t recall which PHV you want.

The script does just two things:

  1. It create a SQL Tuning Set (named s_<<SQLID>>_<<PHV>>) and loads the plan details into it, the goal is to “freeze” it in time so info don’t get lost if the plan is aged out of memory, purged from AWR, etc.
  2. Provide copy&paste instructions to create a Baseline based on the plan in the STS either in the current system or in a remote one. The script DOES NOT execute such steps, only prints them at screen. This way you can read, understand, digest and validate them before YOU execute them.

Hopefully it will make it a little bit easier to play with SPM.

Feedbacks, correction, recommendations are welcome as usual!

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