comnetwork commented on pull request #1970:
URL: https://github.com/apache/hbase/pull/1970#issuecomment-649947198
@Apache9 , I already added comments for `WriteBase.getSyncedLength` like
following:
/**
*NOTE: We add this method for {@link WALFileLengthProvider} used for
replication, considering the
* case if we use {@link AsyncFSWAL},we write to 3 DNs
concurrently,according to the visibility
* guarantee of HDFS, the data will be available immediately when
arriving at DN since all the DNs
* will be considered as the last one in pipeline. This means
replication may read uncommitted data
* and replicate it to the remote cluster and cause data inconsistency.
* The method {@link WriterBase#getLength} may return length which just
in hdfs client buffer and not
* successfully synced to HDFS, so we use this method to return the
length successfully synced to HDFS
* and replication thread could only read writing WAL file limited by
this length.
* see also HBASE-14004 and this document for more details:
*
https://docs.google.com/document/d/11AyWtGhItQs6vsLRIx32PwTxmBY3libXwGXI25obVEY/edit#
*/
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