stack created HBASE-20716:
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Summary: Unsafe access cleanup
Key: HBASE-20716
URL: https://issues.apache.org/jira/browse/HBASE-20716
Project: HBase
Issue Type: Bug
Components: Performance
Reporter: stack
We have two means of getting at unsafe; UnsafeAccess and then internal to the
Bytes class. They are effectively doing the same thing. We should have one
avenue to Unsafe only.
Many of our paths to Unsafe via UnsafeAccess traverse flags to check if access
is available, if it is aligned and the order in which words are written on the
machine. Each check costs -- especially if done millions of times a second --
and on occasion adds bloat in hot code paths. The unsafe access inside Bytes
checks on startup what the machine is capable off and then does a static assign
of the appropriate class-to-use from there on out. UnsafeAccess does not do
this running the checks everytime. Would be good to have the Bytes behavior
pervasive.
The benefit of one access to Unsafe only is plain. The benefits we gain
removing checks will be harder to measure though should be plain when you
disassemble a hot-path; in a (very) rare case, the saved byte codes could be
the difference between inlining or not.
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