Question on Buffer pin/unpin
Dear All,
Simple algorithm to access a buffer is: (I had to deliberately cut out so as not to deviate too much from our primary discussion.)
- Hash data block address (DBA: Combination of tablespace, file_id and block_id) to find hash bucket.
- Get latch protecting hash bucket.
- If (success) then Walk the hash chain reading buffer headers to see if a specific version of the block is already in the chain.
If found, access the buffer in buffer cache, with protection of buffer pin/unpin actions.
If not found, then find a free buffer in buffer cache, unlink the buffer header for that buffer from its current chain, link that buffer header with this hash chain, release the latch and read block in to that free buffer in buffer cache with buffer header pinned.
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