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https://issues.apache.org/jira/browse/HBASE-13520?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14504328#comment-14504328
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Josh Elser commented on HBASE-13520:
------------------------------------
I thought about this for a little bit. I'm undecided on whether or not it's a
good idea to avoid returning null. On one hand, we made the conscious decision
which states "the underlying cell's tags should never be accessed again by this
object". This implies that it would be an error if the caller tries to access
this array when it is null (leads me to think something like {{assert null !=
this.tags}} could be added). On the other hand, we might avoid a future bug if
we fail gracefully to an empty byte array.
I couldn't make up my mind if one was better than the other, so I didn't make a
change. I'm happy to make a change if there are those who are more strongly
opinionated than me :)
> NullPointerException in TagRewriteCell
> --------------------------------------
>
> Key: HBASE-13520
> URL: https://issues.apache.org/jira/browse/HBASE-13520
> Project: HBase
> Issue Type: Bug
> Affects Versions: 1.0.0
> Reporter: Josh Elser
> Assignee: Josh Elser
> Fix For: 2.0.0, 1.1.0, 1.0.2
>
> Attachments: HBASE-13520-v1.patch, HBASE-13520.patch
>
>
> Found via running {{IntegrationTestIngestWithVisibilityLabels}} with Kerberos
> enabled.
> {noformat}
> 2015-04-20 18:54:36,712 ERROR
> [B.defaultRpcServer.handler=17,queue=2,port=16020] ipc.RpcServer: Unexpected
> throwable object
> java.lang.NullPointerException
> at
> org.apache.hadoop.hbase.TagRewriteCell.getTagsLength(TagRewriteCell.java:157)
> at
> org.apache.hadoop.hbase.TagRewriteCell.heapSize(TagRewriteCell.java:186)
> at
> org.apache.hadoop.hbase.CellUtil.estimatedHeapSizeOf(CellUtil.java:568)
> at
> org.apache.hadoop.hbase.regionserver.DefaultMemStore.heapSizeChange(DefaultMemStore.java:1024)
> at
> org.apache.hadoop.hbase.regionserver.DefaultMemStore.internalAdd(DefaultMemStore.java:259)
> at
> org.apache.hadoop.hbase.regionserver.DefaultMemStore.upsert(DefaultMemStore.java:567)
> at
> org.apache.hadoop.hbase.regionserver.DefaultMemStore.upsert(DefaultMemStore.java:541)
> at
> org.apache.hadoop.hbase.regionserver.HStore.upsert(HStore.java:2154)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.increment(HRegion.java:7127)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.increment(RSRpcServices.java:504)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.mutate(RSRpcServices.java:2020)
> at
> org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:31967)
> at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2106)
> at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:101)
> at
> org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:130)
> at org.apache.hadoop.hbase.ipc.RpcExecutor$2.run(RpcExecutor.java:107)
> at java.lang.Thread.run(Thread.java:745)
> {noformat}
> HBASE-11870 tried to be tricky when only the tags of a {{Cell}} need to be
> altered in the write-pipeline by creating a {{TagRewriteCell}} which avoided
> copying all components of the original {{Cell}}. In an attempt to help free
> the tags on the old cell that we wouldn't be referencing anymore,
> {{TagRewriteCell}} nulls out the original {{byte[] tags}}.
> This causes a problem in that the implementation of {{heapSize()}} as it
> {{getTagsLength()}} on the original {{Cell}} instead of the on {{this}}.
> Because the tags on the passed in {{Cell}} (which was also a
> {{TagRewriteCell}}) were null'ed out in the constructor, this results in a
> NPE by the byte array is null.
> I believe this isn't observed in normal, unsecure deployments because there
> is only one RegionObserver/Coprocessor loaded that gets invoked via
> {{postMutationBeforeWAL}}. When there is only one RegionObserver, the
> TagRewriteCell isn't passed another TagRewriteCell, but instead a cell from
> the wire/protobuf. This means that the optimization isn't performed. When we
> have two (or more) observers that a TagRewriteCell passes through (and a new
> TagRewriteCell is created and the old TagRewriteCell's tags array is nulled),
> this enables the described-above NPE.
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