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Kihwal Lee commented on HDFS-5496: ---------------------------------- With 125M blocks in BlocksMap, checking all blocks without adding anything to the under-replicated blocks queue took about 28 seconds. If there is a large number of under-replicated blocks, the initialization time can increase significantly. There is also an issue with the under-replicated blocks queue that make it worse. > Make replication queue initialization asynchronous > -------------------------------------------------- > > Key: HDFS-5496 > URL: https://issues.apache.org/jira/browse/HDFS-5496 > Project: Hadoop HDFS > Issue Type: Improvement > Components: namenode > Reporter: Kihwal Lee > > Today, initialization of replication queues blocks safe mode exit and certain > HA state transitions. For a big name space, this can take hundreds of seconds > with the FSNamesystem write lock held. During this time, important requests > (e.g. initial block reports, heartbeat, etc) are blocked. > The effect of delaying the initialization would be not starting replication > right away, but I think the benefit outweighs. If we make it asynchronous, > the work per iteration should be limited, so that the lock duration is > capped. > If full/incremental block reports and any other requests that modifies block > state properly performs replication checks while the blocks are scanned and > the queues populated in background, every block will be processed. (Some may > be done twice) The replication monitor should run even before all blocks are > processed. > This will allow namenode to exit safe mode and start serving immediately even > with a big name space. It will also reduce the HA failover latency. -- This message was sent by Atlassian JIRA (v6.1#6144)