[HBASE-25065] WAL archival to be done by a separate thread

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.0-alpha-1, 2.4.0
• Fix Version/s: 3.0.0-alpha-1, 2.4.0
• Component/s: wal
• Hadoop Flags: Reviewed
• Assignee: ramkrishna.s.vasudevan
• Reporter: ramkrishna.s.vasudevan
• Created: 18/Sep/20 13:34
• Updated: 10/Nov/20 02:36
• Resolved: 14/Oct/20 10:28

Description

Currently we do clean up of logs once we ensure that the region data has been flushed. We track the sequence number and if we ensure that the seq number has been flushed for any given region and the WAL that was rolled has that seq number then those WAL can be archived.
When we have around ~50 files to archive (per RS) - we do the archiving one after the other. Since archiving is nothing but a rename operation it adds to the meta operation load of Cloud based FS.
Not only that - the entire archival is done inside the rollWriterLock. Though we have closed the writer and created a new writer and the writes are ongoing - we never release the lock until we are done with the archiving.
What happens is that during that period our logs grow in size compared to the default size configured (when we have consistent writes happening).
So the proposal is to move the log archival to a seperate thread and ensure we can do some kind of throttling or batching so that we don't do archival at one shot.

Issue Links

• breaks: HBASE-25186 TestMasterRegionOnTwoFileSystems is failing after HBASE-25065
• links to: GitHub Pull Request #2501
• links to: GitHub Pull Request #2531