Wellington Chevreuil created HBASE-28890:
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Summary: 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
Reporter: Wellington Chevreuil
Assignee: Wellington Chevreuil
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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