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oracleÌåϵ½á¹¹ÉîÈëѧϰBuffer Cache - Overview
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oracleÌåϵ½á¹¹Ö®£ºBuffer Cache - Overview
All Oracle data is obtained by users from the buffer cache. The basic purpose of the cache is to minimize physical
disk I/O by holding (buffering) copies of requested data blocks in memory. Data that is buffered in the cache can
be served to users at memory access speed, much faster than going to disk for it. The large performance penalty of
disk I/O makes tuning the buffer cache an extremely important task for the DBA.
Oracle data is stored on disk in identically sized units called blocks. Block size is determined at database creation
 by the DB_BLOCK_SIZE initialization parameter. The buffer cache is also divided into buffers of this same size, and
 each buffer can hold exactly one database block. Thus, the block is the basic unit of data transfer between disk and
  memory in Oracle.
 
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 oracleÊý¾Ý¿â¸ßËÙ»º´æÖ®Cache Hit Ratio
The buffer cache is a shared resource, accessible by all users. When a user process requests data, Oracle firsts looks
 for that data's block in the cache. If the data is buffered in the cache it is returned to the requ


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