How do I find buffer cache hit ratio in SQL?
Table of Contents
How do I find buffer cache hit ratio in SQL?
Buffer cache hit ratio The ratio is the total number of cache hits divided by the total number of cache lookups over the last few thousand page accesses.
What should buffer cache hit ratio be?
There is no standard metric for the buffer cache hit ratio. Our recommended value for it is over 90. When better performance is needed, the minimal acceptable value is 95. A lower value indicates a memory problem.
What is buffer cache hit ratio in Oracle?
The buffer cache hit ratio calculates how often a requested block has been found in the buffer cache without requiring disk access. This ratio is computed using data selected from the V$SYSSTAT performance view. Use the buffer cache hit ratio to verify the physical I/O as predicted by the V$DB_CACHE_ADVICE view.
How do you calculate buffer hit ratio?
The best way to calculate a cache hit ratio is to divide the total number of cache hits by the sum of the total number of cache hits, and the number of cache misses. This value is usually presented in the percentage of the requests or hits to the applicable cache.
What is Db_keep_cache_size?
DB_KEEP_CACHE_SIZE specifies the size of the KEEP buffer pool. The size of the buffers in the KEEP buffer pool is the primary block size (the block size defined by the DB_BLOCK_SIZE initialization parameter).
Can it be possible to have 100% hit in a cache?
That is not mathematically possible.
How do I check my PGA usage?
Show PGA usage of sessions
- SELECT SID, b. NAME, ROUND (a. VALUE / (1024 * 1024), 2) MB.
- WHERE ( NAME LIKE ‘%session uga memory%’
- OR NAME LIKE ‘%session pga memory%’)
- AND a. statistic# = b.statistic#
- ORDER BY ROUND (a. VALUE / (1024 * 1024), 2) DESC.
What is DB cache size?
DB_CACHE_SIZE specifies the size of the DEFAULT buffer pool for buffers with the primary block size (the block size defined by the DB_BLOCK_SIZE initialization parameter). The value must be at least 4M * number of cpus * granule size (smaller values are automatically rounded up to this value).
How do I keep the table in buffer cache?
Keep Table in Buffer Pool Oracle 11g
- Keep Table in Buffer Pool. SQL> alter table testtable storage (buffer_pool keep);
- Remove Table From Buffer Pool.
- ALTER TABLE testtable STORAGE (buffer_pool keep) command places the table in a special section of the cache called the KEEP buffer pool.
How do I check my cache hit ratio?
How is hit ratio calculated?
To calculate a hit ratio, divide the number of cache hits with the sum of the number of cache hits, and the number of cache misses. For example, if you have 51 cache hits and three misses over a period of time, then that would mean you would divide 51 by 54. The result would be a hit ratio of 0.944.
