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https://issues.apache.org/jira/browse/HBASE-28890?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Wellington Chevreuil resolved HBASE-28890.
------------------------------------------
Resolution: Fixed
Merged into master, branch-3, branch-2, branch-2.6 and branch-2.5.
> RefCnt Leak error when caching index blocks at write time
> ---------------------------------------------------------
>
> Key: HBASE-28890
> URL: https://issues.apache.org/jira/browse/HBASE-28890
> Project: HBase
> Issue Type: Bug
> Affects Versions: 3.0.0-beta-1, 2.7.0, 2.6.1, 2.5.10
> Reporter: Wellington Chevreuil
> Assignee: Wellington Chevreuil
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.0.0, 2.7.0, 2.5.11, 2.6.2
>
>
> Following [~bbeaudreault] works from HBASE-27170 that added the (very useful)
> refcount leak detector, we sometimes see these reports on some branch-2 based
> deployments:
> {noformat}
> 2024-09-25 10:06:42,413 ERROR
> org.apache.hbase.thirdparty.io.netty.util.ResourceLeakDetector: LEAK:
> RefCnt.release() was not called before it's garbage-collected. See
> https://netty.io/wiki/reference-counted-objects.html for more information.
> Recent access records:
> Created at:
> org.apache.hadoop.hbase.nio.RefCnt.<init>(RefCnt.java:59)
> org.apache.hadoop.hbase.nio.RefCnt.create(RefCnt.java:54)
> org.apache.hadoop.hbase.nio.ByteBuff.wrap(ByteBuff.java:550)
>
> org.apache.hadoop.hbase.io.ByteBuffAllocator.allocate(ByteBuffAllocator.java:357)
>
> org.apache.hadoop.hbase.io.hfile.HFileBlock$Writer.cloneUncompressedBufferWithHeader(HFileBlock.java:1153)
>
> org.apache.hadoop.hbase.io.hfile.HFileBlock$Writer.getBlockForCaching(HFileBlock.java:1215)
>
> org.apache.hadoop.hbase.io.hfile.HFileBlockIndex$BlockIndexWriter.lambda$writeIndexBlocks$0(HFileBlockIndex.java:997)
> java.base/java.util.Optional.ifPresent(Optional.java:178)
>
> org.apache.hadoop.hbase.io.hfile.HFileBlockIndex$BlockIndexWriter.writeIndexBlocks(HFileBlockIndex.java:996)
>
> org.apache.hadoop.hbase.io.hfile.HFileWriterImpl.close(HFileWriterImpl.java:635)
>
> org.apache.hadoop.hbase.regionserver.StoreFileWriter.close(StoreFileWriter.java:378)
>
> org.apache.hadoop.hbase.regionserver.StoreFlusher.finalizeWriter(StoreFlusher.java:69)
>
> org.apache.hadoop.hbase.regionserver.DefaultStoreFlusher.flushSnapshot(DefaultStoreFlusher.java:74)
>
> org.apache.hadoop.hbase.regionserver.HStore.flushCache(HStore.java:831)
>
> org.apache.hadoop.hbase.regionserver.HStore$StoreFlusherImpl.flushCache(HStore.java:2033)
>
> org.apache.hadoop.hbase.regionserver.HRegion.internalFlushCacheAndCommit(HRegion.java:2878)
>
> org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:2620)
>
> org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:2592)
>
> org.apache.hadoop.hbase.regionserver.HRegion.flushcache(HRegion.java:2462)
>
> org.apache.hadoop.hbase.regionserver.MemStoreFlusher.flushRegion(MemStoreFlusher.java:602)
>
> org.apache.hadoop.hbase.regionserver.MemStoreFlusher.flushRegion(MemStoreFlusher.java:572)
>
> org.apache.hadoop.hbase.regionserver.MemStoreFlusher.access$1000(MemStoreFlusher.java:65)
>
> org.apache.hadoop.hbase.regionserver.MemStoreFlusher$FlushHandler.run(MemStoreFlusher.java:344)
> {noformat}
> It turns out that we always convert the block to a "on-heap" one, inside
> LruBlockCache.cacheBlock, so when the index block is a SharedMemHFileBlock,
> the blockForCaching instance in the code
> [here|https://github.com/apache/hbase/blob/master/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlockIndex.java#L1076]
> becomes eligible for GC without releasing buffers/decreasing refcount
> (leak), right after we return the BlockIndexWriter.writeIndexBlocks call.
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