Yi Liu created HDFS-6784: ---------------------------- Summary: Avoid rescan twice in HDFS CacheReplicationMonitor for one FS Op if it calls setNeedsRescan multiple times. Key: HDFS-6784 URL: https://issues.apache.org/jira/browse/HDFS-6784 Project: Hadoop HDFS Issue Type: Improvement Components: caching Affects Versions: 3.0.0 Reporter: Yi Liu Assignee: Yi Liu
In HDFS CacheReplicationMonitor, rescan is expensive. Sometimes, {{setNeedsRescan}} is called multiple times, for example, in FSNamesystem#modifyCacheDirective, there are 3 times. In monitor thread of CacheReplicationMonitor, if it checks {{needsRescan}} is true, rescan will happen, but {{needsRescan}} is set to false before real scan. Meanwhile, the 2nd or 3rd time {{setNeedsResacn}} may set {{needsRescan}} to true. So after the scan finish, in next loop, a new rescan will be triggered, that's not necessary at all and inefficient for rescan twice. -- This message was sent by Atlassian JIRA (v6.2#6252)