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What is the state of Cache buffer, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

Buffer States

The database uses internal algorithms to manage buffers in the cache. Buffers can be in any of the following mutually exclusive states:

■ Unused

The buffer is available because it has never been used or is not currently in use. This type of buffer is the easiest to use in the database.

■ Clean

This buffer has been used before and now contains a read-consistent version of the block at a point in time. The block contains data, but is "clean", so it does not need to be checked. The database can lock the block and reuse it.

■ Dirty

The buffer contains modified data that has not been written to disk. The database must check the block before reusing it.

Each buffer has an access mode: fixed or idle (unpinned). The buffer is "fixed" in the cache so that when a user session accesses it, it does not age due to insufficient memory. Multiple sessions cannot modify fixed buffers at the same time.

The database uses complex algorithms to improve buffer access efficiency. Pointers to dirty and non-dirty buffers exist in the same least recently used (LRU) list, which has a hot end and a cold end. Cold buffers are buffers that have not been used recently. Hot buffers are frequently accessed and have recently been used

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