[ https://issues.apache.org/jira/browse/HDFS-4270?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Derek Dagit updated HDFS-4270: ------------------------------ Attachment: HDFS-4270.patch Re-attaching patch, as the errors reported by the bot appear to be transient. > Replications of the highest priority should be allowed to choose a source > datanode that has reached its max replication limit > ----------------------------------------------------------------------------------------------------------------------------- > > Key: HDFS-4270 > URL: https://issues.apache.org/jira/browse/HDFS-4270 > Project: Hadoop HDFS > Issue Type: Bug > Components: namenode > Affects Versions: 3.0.0, 0.23.5 > Reporter: Derek Dagit > Assignee: Derek Dagit > Priority: Minor > Attachments: HDFS-4270-branch-0.23.patch, HDFS-4270.patch, > HDFS-4270.patch > > > Blocks that have been identified as under-replicated are placed on one of > several priority queues. The highest priority queue is essentially reserved > for situations in which only one replica of the block exists, meaning it > should be replicated ASAP. > The ReplicationMonitor periodically computes replication work, and a call to > BlockManager#chooseUnderReplicatedBlocks selects a given number of > under-replicated blocks, choosing blocks from the highest-priority queue > first and working down to the lowest priority queue. > In the subsequent call to BlockManager#computeReplicationWorkForBlocks, a > source for the replication is chosen from among datanodes that have an > available copy of the block needed. This is done in > BlockManager#chooseSourceDatanode. > chooseSourceDatanode's job is to choose the datanode for replication. It > chooses a random datanode from the available datanodes that has not reached > its replication limit (preferring datanodes that are currently > decommissioning). > However, the priority queue of the block does not inform the logic. If a > datanode holds the last remaining replica of a block and has already reached > its replication limit, the node is dismissed outright and the replication is > not scheduled. > In some situations, this could lead to data loss, as the last remaining > replica could disappear if an opportunity is not taken to schedule a > replication. It would be better to waive the max replication limit in cases > of highest-priority block replication. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira