BUFFER HIT RATIO NOTES
2010.06.15 20:37
원문 : http://www.ischo.net -- 조인상 // 시스템 엔지니어
Writer : http://www.ischo.net -- ischo // System Engineer in Replubic Of Korea
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원문 : http://www.ischo.net -- 조인상 //시스템 엔지니어
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BUFFER HIT RATIO NOTES:
Consistent Gets - The number of accesses made to the block buffer to retrieve data in a consistent mode.
DB Blk Gets - The number of blocks accessed via single block gets (i.e. not through the consistent get mechanism).
Physical Reads - The cumulative number of blocks read from disk.
Logical reads are the sum of consistent gets and db block gets.
The db block gets statistic value is incremented when a block is read for update and when segment header blocks are accessed.
The buffer hit ratio (also known as read hit ratio) is one indicator that identifies whether to add more database block buffers. This buffer hit ratio identifies the difference between the number of reads from disk versus memory (found in the database block buffers).If your system is highly interactive, then a good rule of thumb is to ensure the buffer hit ratio is greater than 95 percent. If your system is highly batch reporting, then a good rule of thumb is to ensure the buffer hit ratio is greater than 85 percent. Keep in mind it is much faster to find data in memory than going to disk, therefore, if there is memory to increase the database block buffers without hurting system resources, then more memory should be added to this area to increase these percentages.
Hit Ratio should be > 85%, else increase DB_BLOCK_BUFFERS in init.ora
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BUFFER HIT RATIO NOTES:
