[HBASE-11226] Document and increase the default value for hbase.hstore.flusher.count

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.99.0, 0.98.2
• Fix Version/s: 0.99.0, 0.98.3
• Component/s: regionserver
• Hadoop Flags: Reviewed
• Assignee: Nicolas Liochon
• Reporter: Nicolas Liochon
• Created: 21/May/14 16:34
• Updated: 21/Feb/15 23:29
• Resolved: 23/May/14 17:48

Description

HBASE-6466 add the possibility to have multiple threads for the flusher.
The default value is 1, but this should be incremented to 2 reasons:

• I've observed that the flush of a region can be delayed because another is in progress. During a write load, this leads to an increased latency because the memstore size increases and then block the client
• if, by accident, a flusher hits a slow or bad datanode, all the flush will have to wait until the timeouts expires. With 2 or more flushers and some luck the other regions will be flushed by the second thread.

Lastly this setting is important enough to be documented in the standard hbase site imho.

I think it's important enough to go in the .98 branch as well
There will be an impact: as the flush won't be queued (or less queued) we may have more compactions...