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https://issues.apache.org/jira/browse/HBASE-22422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16840955#comment-16840955
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Zheng Hu commented on HBASE-22422:
----------------------------------
Another risk is here, LruBlockCache#evictBlock, we should move the
previous.getBuffer().release() to the last line before return because once the
release decrease the refCnt to zero then nobody can access the buf (such as
victimHandler).
{code}
protected long evictBlock(LruCachedBlock block, boolean
evictedByEvictionProcess) {
LruCachedBlock previous = map.remove(block.getCacheKey());
if (previous == null) {
return 0;
}
// Decrease the block's reference count, and if refCount is 0, then it'll
auto-deallocate.
previous.getBuffer().release();
updateSizeMetrics(block, true);
long val = elements.decrementAndGet();
if (LOG.isTraceEnabled()) {
long size = map.size();
assertCounterSanity(size, val);
}
if (block.getBuffer().getBlockType().isData()) {
dataBlockElements.decrement();
}
if (evictedByEvictionProcess) {
// When the eviction of the block happened because of invalidation of
HFiles, no need to
// update the stats counter.
stats.evicted(block.getCachedTime(), block.getCacheKey().isPrimary());
if (victimHandler != null) {
victimHandler.cacheBlock(block.getCacheKey(), block.getBuffer());
}
}
return block.heapSize();
}
{code}
> Retain an ByteBuff with refCnt=0 when getBlock from LRUCache
> ------------------------------------------------------------
>
> Key: HBASE-22422
> URL: https://issues.apache.org/jira/browse/HBASE-22422
> Project: HBase
> Issue Type: Sub-task
> Components: BlockCache
> Reporter: Zheng Hu
> Assignee: Zheng Hu
> Priority: Major
> Attachments: LRUBlockCache-getBlock.png,
> image-2019-05-15-12-00-03-641.png
>
>
> After runing YCSB scan/get benchmark in our XiaoMi cluster, we found the get
> QPS dropped from 25000/s to hunderds per second in a cluster with five
> nodes.
> After enable the debug log at YCSB client side, I found the following
> stacktrace , see
> https://issues.apache.org/jira/secure/attachment/12968745/image-2019-05-15-12-00-03-641.png
> Need a patch to fix this.
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