Darrel Schneider created GEODE-9499:
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Summary: RedisData does not need an object reference to implement
Delta
Key: GEODE-9499
URL: https://issues.apache.org/jira/browse/GEODE-9499
Project: Geode
Issue Type: Improvement
Components: redis
Reporter: Darrel Schneider
Currently every redis data structure implements the RedisData interface. Part
of that implementation is Delta support. The way it is implemented is by
storing a reference to a DeltaInfo instance in each RedisData. Most of the time
this reference is null but it still takes up 8 bytes (4 if oops are
compressed). It is only non-null while an update is in progress.
What we could do instead is store the reference to the DeltaInfo in a thread
local. That works because we are careful to run each redis command that
modifies a RedisData on the primary. We lock the primary down during the
operation to prevent it from moving. So when it comes time for the primary to
call toDelta on the RedisData instance to distribute it to the secondary, this
call will done on the same thread so our hasDelta and toDelta can just read the
ThreadLocal. This will save us one object reference for every redis key we
store.
Something else we could consider doing is to pass the DeltaInfo as the callback
arg when we do the region put. But this would require change to core geode to
detect that the callback arg is a DeltaInfo and to use it to compute the delta
bytes that are stored on the EntryEventImpl. This is doable and may even
perform better but would require changes to the core. It would probably be a
bit faster than the ThreadLocal solution just because of the extra latency in
setting and reading a ThreadLocal compared to a stack parameter
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