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https://issues.apache.org/jira/browse/HBASE-14004?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16184854#comment-16184854
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stack commented on HBASE-14004:
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[~Apache9] Any chance of a release note here please boss? This is a great fix.
Would be a shame for it to go under the radar. The release note will help folks
realize what has happened in here.
> [Replication] Inconsistency between Memstore and WAL may result in data in
> remote cluster that is not in the origin
> -------------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-14004
> URL: https://issues.apache.org/jira/browse/HBASE-14004
> Project: HBase
> Issue Type: Bug
> Components: regionserver, Replication
> Reporter: He Liangliang
> Assignee: Duo Zhang
> Priority: Critical
> Labels: replication, wal
> Fix For: 2.0.0-alpha-4
>
> Attachments: HBASE-14004.patch, HBASE-14004-v1.patch,
> HBASE-14004-v2.patch, HBASE-14004-v2.patch, HBASE-14004-v3.patch
>
>
> Looks like the current write path can cause inconsistency between
> memstore/hfile and WAL which cause the slave cluster has more data than the
> master cluster.
> The simplified write path looks like:
> 1. insert record into Memstore
> 2. write record to WAL
> 3. sync WAL
> 4. rollback Memstore if 3 fails
> It's possible that the HDFS sync RPC call fails, but the data is already
> (may partially) transported to the DNs which finally get persisted. As a
> result, the handler will rollback the Memstore and the later flushed HFile
> will also skip this record.
> ==================================
> This is a long lived issue. The above problem is solved by write path
> reorder, as now we will sync wal first before modifying memstore. But the
> problem may still exists as replication thread may read the new data before
> we return from hflush. See this document for more details:
> https://docs.google.com/document/d/11AyWtGhItQs6vsLRIx32PwTxmBY3libXwGXI25obVEY/edit#
> So we need to keep a sync length in WAL and tell replication wal reader this
> is limit when you read this wal file.
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