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https://issues.apache.org/jira/browse/HBASE-14178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14659553#comment-14659553
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Heng Chen commented on HBASE-14178:
-----------------------------------
{quote}
Why we need different condition for reading from the cache with and with out
lock? with out lock we do at first , as an optimistic approach. If block is not
there by then, we are doing one more round of check for a possible another
concurrent thread doing the caching of this block. So we use lock then. So am
not sure whether to read from cache why it has to have different condition.
Looks like the patch tend to make an impression that we will read from cache
with lock in order to cache that block into the BC. But it is not the case.
Sorry if I missed some other discussion parts in above comments
{quote}
Thanks for your reply!
The lock purpose is to improve the perf when other thread read same block. If
we make sure the block is not in BC, there is no need to lock. So in
{{shouldLockOnCacheMiss}} , we will check if the block will be cached after
read from hdfs.
> regionserver blocks because of waiting for offsetLock
> -----------------------------------------------------
>
> Key: HBASE-14178
> URL: https://issues.apache.org/jira/browse/HBASE-14178
> Project: HBase
> Issue Type: Bug
> Components: regionserver
> Affects Versions: 0.98.6
> Reporter: Heng Chen
> Priority: Critical
> Fix For: 0.98.6
>
> Attachments: HBASE-14178-0.98.patch, HBASE-14178.patch,
> HBASE-14178_v1.patch, HBASE-14178_v2.patch, HBASE-14178_v3.patch,
> HBASE-14178_v4.patch, HBASE-14178_v5.patch, HBASE-14178_v6.patch, jstack
>
>
> My regionserver blocks, and all client rpc timeout.
> I print the regionserver's jstack, it seems a lot of threads were blocked
> for waiting offsetLock, detail infomation belows:
> PS: my table's block cache is off
> {code}
> "B.DefaultRpcServer.handler=2,queue=2,port=60020" #82 daemon prio=5 os_prio=0
> tid=0x0000000001827000 nid=0x2cdc in Object.wait() [0x00007f3831b72000]
> java.lang.Thread.State: WAITING (on object monitor)
> at java.lang.Object.wait(Native Method)
> at java.lang.Object.wait(Object.java:502)
> at org.apache.hadoop.hbase.util.IdLock.getLockEntry(IdLock.java:79)
> - locked <0x0000000773af7c18> (a
> org.apache.hadoop.hbase.util.IdLock$Entry)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2.readBlock(HFileReaderV2.java:352)
> at
> org.apache.hadoop.hbase.io.hfile.HFileBlockIndex$BlockIndexReader.loadDataBlockWithScanInfo(HFileBlockIndex.java:253)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2$AbstractScannerV2.seekTo(HFileReaderV2.java:524)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2$AbstractScannerV2.reseekTo(HFileReaderV2.java:572)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseekAtOrAfter(StoreFileScanner.java:257)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(StoreFileScanner.java:173)
> at
> org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner.doRealSeek(NonLazyKeyValueScanner.java:55)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.generalizedSeek(KeyValueHeap.java:313)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.requestSeek(KeyValueHeap.java:269)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.reseek(StoreScanner.java:695)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.seekAsDirection(StoreScanner.java:683)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.next(StoreScanner.java:533)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.next(KeyValueHeap.java:140)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.populateResult(HRegion.java:3889)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:3969)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:3847)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.next(HRegion.java:3820)
> - locked <0x00000005e5c55ad0> (a
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.next(HRegion.java:3807)
> at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:4779)
> at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:4753)
> at
> org.apache.hadoop.hbase.regionserver.HRegionServer.get(HRegionServer.java:2916)
> at
> org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:29583)
> at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2027)
> at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:108)
> at
> org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:114)
> at org.apache.hadoop.hbase.ipc.RpcExecutor$1.run(RpcExecutor.java:94)
> at java.lang.Thread.run(Thread.java:745)
> Locked ownable synchronizers:
> - <0x00000005e5c55c08> (a
> java.util.concurrent.locks.ReentrantLock$NonfairSync)
> {code}
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