Buffer pool or buffer cache is a memory structure within Oracle SGA that is used for caching data blocks in the memory. Accessing data from the memory is significantly faster than accessing data from disk. The goal of block buffer tuning is to efficiently cache frequently used data blocks in the buffer cache (SGA) and provide faster access to data.
Tuning block buffer is a key task in any Oracle tuning initiative and is a part of an ongoing tuning and monitoring of production databases. The task of database performance optimization by allocating appropriate memory structure within SGA is a very interesting and challenging task for a DBA. Generally, it takes a few iterations before you can reach to a satisfactory memory allocation. This article presents a tuning approach that greatly simplifies the tuning effort. The methodology discussed here will help DBAs in creating a proactive database tuning and monitoring strategy for their production databases. If you are a DBA responsible for tuning a database without enough physical memory on the server, you will find this article very informative and useful. With the help of an established methodology and tuning strategy, you can easily identify the problem areas and tune the SGA memory structure.
- Identify the amount of memory that you can allocate to block buffers. Create buffer pool without inducing significant paging or swapping.
- Identify how frequently data blocks are accessed from the buffer cache (a. k. a Block Buffer Hit Ratio).
- Identify frequently used and rarely used data blocks. Cache frequently used blocks and discard rarely used blocks.
- Assign tables to KEEP / RECYCLE pool. Identify buffer hit ratio for KEEP, RECYCLE, and DEFAULT pool. Adjust the initialization parameters for optimum performance.
- Identify the amount of memory needed to maintain required performance.
Using this methodical approach, a DBA can easily identify the problem areas, and tune the database block buffers. The DBA can create the following buffer pool to efficiently cache data blocks in SGA:
KEEP
Cache tables that are very critical for system performance. Typically, lookup tables are very good candidates for the KEEP pool. The DBA should create the KEEP pool large enough to maintain 99% buffer hit ratio on this pool.
RECYCLE
Cache tables that are not critical for system performance. Typically, a table containing historical information that is either rarely queried or used by batch process is a good candidate for the RECYCLE pool. The DBA should create the RECYCLE pool large enough to finish the current transaction.
DEFAULT
Cache tables that do not belong to either KEEP or RECYCLE pool.
The DBA can setup OEM jobs, Oracle statspack, or custom monitoring scripts to monitor your production database block buffer efficiency, and to identify and tune the problem area.
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