Oracle Point, Oracle Life.

in Oracle,

“The redo log buffer is a circular buffer in the SGA that holds information about changes made to the database. This information is stored in redo entries. Redo entries contain the information necessary to reconstruct, or redo, changes made to the database by INSERT, UPDATE, DELETE, CREATE, ALTER, or DROP operations. Redo entries are used for database recovery, if necessary.

Redo entries are copied by Oracle server processes from the user’s memory space to the redo log buffer in the SGA. The redo entries take up continuous, sequential space in the buffer. The background process LGWR writes the redo log buffer to the active online redo log file (or group of files) on disk.”

In Oracle 9i,  Maximum of Log Buffer is 512 KB or 128 KB * CPU_COUNT, whichever is greater. And, it’s adjustable.

In Oracle 10g, Log_buffer can no longer be modified and will be set by default by Oracle.

(Script to “Check how often user process has to wait for space in the redo log buffer”)

Popularity: 6% [?]

in Oracle,

“The library cache includes the shared SQL areas, private SQL areas (in the case of a multiple transaction server), PL/SQL procedures and packages, and control structures such as locks and library cache handles.

Shared SQL areas are accessible to all users, so the library cache is contained in the shared pool within the SGA.”

To tune Library Cache, we also need to calculate GetHit Ratio and PinHit Ratio.

(Script to “Calculate GetHit Ratio and PinHit Ratio of Library Cache”)

Also, reference the scripts offered at http://www.dba-oracle.com/concepts/pinned_objects.htm

There are two scripts useful there.

• Show Objects Which Should Be Kept
• use DBMS_SHARED_POOL.KEEP to retain object in library cache

Besides of above, Parse Ratio and Recursive Call Ratio also need to be paid attention to.

(Script for “Calculate Parse Ratio and Recursive Call Ratio of Library Cache”)

Popularity: 5% [?]