[ https://issues.apache.org/jira/browse/HDFS-15150?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Ahmed Hussein reopened HDFS-15150: ---------------------------------- Thanks [~sodonnell] and [~weichiu] for introducing this optimization. I am opening the issue in order to submit patches backporting the changes to branches 2.10 - 3.x > Introduce read write lock to Datanode > ------------------------------------- > > Key: HDFS-15150 > URL: https://issues.apache.org/jira/browse/HDFS-15150 > Project: Hadoop HDFS > Issue Type: Improvement > Components: datanode > Affects Versions: 3.3.0 > Reporter: Stephen O'Donnell > Assignee: Stephen O'Donnell > Priority: Major > Fix For: 3.3.0 > > Attachments: HDFS-15150.001.patch, HDFS-15150.002.patch, > HDFS-15150.003.patch > > > HDFS-9668 pointed out the issues around the DN lock being a point of > contention some time ago, but that Jira went in a direction of creating a new > FSDataset implementation which is very risky, and activity on the Jira has > stalled for a few years now. Edit: Looks like HDFS-9668 eventually went in a > similar direction to what I was thinking, so I will review that Jira in more > detail to see if this one is necessary. > I feel there could be significant gains by moving to a ReentrantReadWrite > lock within the DN. The current implementation is simply a ReentrantLock so > any locker blocks all others. > Once place I think a read lock would benefit us significantly, is when the DN > is serving a lot of small blocks and there are jobs which perform a lot of > reads. The start of reading any blocks right now takes the lock, but if we > moved this to a read lock, many reads could do this at the same time. > The first conservative step, would be to change the current lock and then > make all accesses to it obtain the write lock. That way, we should keep the > current behaviour and then we can selectively move some lock accesses to the > readlock in separate Jiras. > I would appreciate any thoughts on this, and also if anyone has attempted it > before and found any blockers. -- This message was sent by Atlassian Jira (v8.3.4#803005) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-dev-unsubscr...@hadoop.apache.org For additional commands, e-mail: hdfs-dev-h...@hadoop.apache.org