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https://issues.apache.org/jira/browse/ARROW-6723?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Liya Fan closed ARROW-6723.
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Resolution: Won't Fix
This change is not guaranteed to be safe.
In addition, different ArrowBuf have separate allocation manangers, so it does
not lead to resource contention for most scenarios.
> [Java] Reduce the range of synchronized block when releasing an ArrowBuf
> ------------------------------------------------------------------------
>
> Key: ARROW-6723
> URL: https://issues.apache.org/jira/browse/ARROW-6723
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Java
> Reporter: Liya Fan
> Assignee: Liya Fan
> Priority: Major
> Labels: pull-request-available
> Time Spent: 1h 50m
> Remaining Estimate: 0h
>
> When releasing an ArrowBuf, we will run the following piece of code:
> private int decrement(int decrement) {
> allocator.assertOpen();
> final int outcome;
> synchronized (allocationManager) {
> outcome = bufRefCnt.addAndGet(-decrement);
> if (outcome == 0) {
> lDestructionTime = System.nanoTime();
> allocationManager.release(this);
> }
> }
> return outcome;
> }
> It can be seen that we need to acquire the lock for allocation manager lock,
> no matter if we need to release the buffer. In addition, the operation of
> decrementing refcount is only carried out after the lock is acquired. This
> leads to unnecessary resource contention, and may degrade performance.
> We propose to change the code like this:
> private int decrement(int decrement) {
> allocator.assertOpen();
> final int outcome;
> outcome = bufRefCnt.addAndGet(-decrement);
> if (outcome == 0) {
> lDestructionTime = System.nanoTime();
> synchronized (allocationManager) {
> allocationManager.release(this);
> }
> }
> return outcome;
> }
> Note that this change can be dangerous, as it lies in the core of our code
> base, so we should be careful with it. On the other hand, it may have
> non-trivial performance implication. As far as I know, when a distributed
> task is getting closed, a large number of ArrowBuf will be closed
> simultaneously. If we reduce the range of the synchronization block, we can
> significantly improve the performance.
> What do you think?
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