Speed up simultaneous reads of a block when block caching is turned off
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Key: HBASE-5000
URL: https://issues.apache.org/jira/browse/HBASE-5000
Project: HBase
Issue Type: Bug
Reporter: Mikhail Bautin
Priority: Minor
With block caching, when one client starts reading a block and another one
comes around asking for the same block, the second client waits for the first
one to finish reading and returns the block from cache. This is achieved by
locking on the block offset using IdLock, a "sparse lock" primitive allowing to
lock on arbitrary long numbers. However, in case there is no block caching,
there is no reason to wait for other clients that are reading the same block.
One challenge optimizing this that we don't necessary have accurate information
about whether other HFile API clients interested in the block would cache it.
Setting priority as minor, as it is very unusual to turn off block caching.
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