A hot buffer is frequently accessed and has been recently used. Pointers to dirty and nondirty buffers exist on the same least recently used (LRU) list, which has a hot end and cold end.Ī cold buffer is one that has not been recently used. The database uses a sophisticated algorithm to make buffer access efficient. Multiple sessions cannot modify a pinned buffer at the same time. The database must checkpoint the block before reusing it.Įvery buffer has an access mode: pinned or free (unpinned).Ī buffer is "pinned" in the cache so that it does not age out of memory while a user session accesses it. The buffer contain modified data that has not yet been written to disk. The database can pin the block and reuse it. The block contains data but is "clean" so it does not need to be checkpointed.
This buffer was used earlier and now contains a read-consistent version of a block as of a point in time. This type of buffer is the easiest for the database to use.
The buffer is available for use because it has never been used or is currently unused. The database can improve performance by caching buffers in flash memory instead of reading from magnetic disk.ĭatabase Smart Flash Cache is available only in Solaris and Oracle Enterprise Linux.Ī buffer can be in any of the following mutually exclusive states: This buffer cache extension is stored on a flash disk device, which is a solid state storage device that uses flash memory. When Database Smart Flash Cache (flash cache) is enabled, part of the buffer cache can reside in the flash cache. > Keep frequently accessed blocks in the buffer cache and write infrequently accessed blocks to disk
Instead, database wirter (DBWn) performs lazy writes in the background. After a COMMIT, the database writes the redo buffers to disk but does not immediately write data blocks to disk. The database updates data blocks in the cache and stores metadata about the changes in the redo log buffer. The buffer cache to achieve the following goals: All users concurrently connected to a database instance share access to the buffer cache. A buffer is a main memory address in which the buffer manager temporarily caches a currently or recently used data block. The database buffer cache, also called the buffer cache, is the memory area that stores copies of data blocks read from data files. Oracle Memory Architecture-Oracle 体系结构篇 2 1.
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