Implications of Setting Oracle9iR2’s Statistics Collection Level

Concerned about looking at statistics within Oracle? You should
take a quick look at Oracles’ new method of turning collections on or off.

It’s New

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.

Its Settings

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