Implications of Setting Oracle9iR2's Statistics Collection Level
April 2, 2003
Concerned about looking at statistics within Oracle? You should take a quick look at Oracles' new method of turning collections on or off.
In Oracle9iR2, Oracle has introduced a new initialization parameter called STATISTICS_LEVEL. Through this parameter, Oracle gives you the option to set different levels of statistical collection for major statistics and advisories.
There are three settings for this parameter: BASIC, TYPICAL, and ALL. The default setting is TYPICAL. Here is a quick matrix of what statistics and advisories are turned on depending on the setting you choose. I have added two columns to this matrix. The first is Session Affected which indicates those statistics that are affected by issuing the ALTER SESSION command for the STATISTICS_LEVEL parameter. The second is the initialization parameter that you can set in the SPFILE to override the STATISTICS_LEVEL setting.
To take a look at the advisories and statistics controlled by the setting of the STATISTICS_LEVEL parameter or the entries in the SPFILE and what their current settings are, just issue the following SQL:
col statistics_name for a30 head "Statistics Name" col session_status for a10 head "Session|Status" col system_status for a10 head "System|Status" col activation_level for a10 head "Activation|Level" col session_settable for a10 head "Session|Settable" SELECT STATISTICS_NAME, SESSION_STATUS, SYSTEM_STATUS, ACTIVATION_LEVEL, SESSION_SETTABLE FROM v$statistics_level ORDER BY 1 / Session System Activation Session Statistics Name Status Status Level Settable ------------------------------ ---------- ---------- ---------- ---------- Buffer Cache Advice ENABLED ENABLED TYPICAL NO MTTR Advice ENABLED ENABLED TYPICAL NO PGA Advice ENABLED ENABLED TYPICAL NO Plan Execution Statistics DISABLED DISABLED ALL YES Segment Level Statistics ENABLED ENABLED TYPICAL NO Shared Pool Advice ENABLED ENABLED TYPICAL NO Timed OS Statistics DISABLED DISABLED ALL YES Timed Statistics ENABLED ENABLED TYPICAL YES