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https://issues.apache.org/jira/browse/HBASE-2646?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12874180#action_12874180
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Jeff Whiting commented on HBASE-2646:
-------------------------------------
That is great news to hear about optimizations being made on the compaction
queue. Looking at HBASE-2375 I see a lot of improvement in how the compaction
is being done and being more intelligent on when to compact and split but I
don't seem to see any prioritization of the compaction requests (I may be
overlooking it). Maybe some of the improvements in the patch here would
integrate nicely with what is already being done? It seems that whenever the an
action is blocking on a compaction that the request should take precedence.
But that is just my two cents.
> Compaction requests should be prioritized to prevent blocking
> -------------------------------------------------------------
>
> Key: HBASE-2646
> URL: https://issues.apache.org/jira/browse/HBASE-2646
> Project: HBase
> Issue Type: Improvement
> Components: regionserver
> Affects Versions: 0.20.4
> Environment: ubuntu server 10; hbase 0.20.4; 4 machine cluster (each
> machine is an 8 core xeon with 16 GB of ram and 6TB of storage); ~250 Million
> rows;
> Reporter: Jeff Whiting
> Attachments: prioritycompactionqueue-0.20.4.patch
>
>
> While testing the write capacity of a 4 machine hbase cluster we were getting
> long and frequent client pauses as we attempted to load the data. Looking
> into the problem we'd get a relatively large compaction queue and when a
> region hit the "hbase.hstore.blockingStoreFiles" limit it would get block the
> client and the compaction request would get put on the back of the queue
> waiting for many other less important compactions. The client is basically
> stuck at that point until a compaction is done. Prioritizing the compaction
> requests and allowing the request that is blocking other actions go first
> would help solve the problem.
> You can see the problem by looking at our log files:
> You'll first see an event such as a too many HLog which will put a lot of
> requests on the compaction queue.
> {noformat}
> 2010-05-25 10:53:26,570 INFO org.apache.hadoop.hbase.regionserver.HLog: Too
> many hlogs: logs=33, maxlogs=32; forcing flush of 22 regions(s):
> responseCounts,RS_6eZzLtdwhGiTwHy,1274232223324,
> responses,RS_0qhkL5rUmPCbx3K-1274213057242,1274513189592,
> responses,RS_1ANYnTegjzVIsHW-12742177419
> 21,1274511001873, responses,RS_1HQ4UG5BdOlAyuE-1274216757425,1274726323747,
> responses,RS_1Y7SbqSTsZrYe7a-1274328697838,1274478031930,
> responses,RS_1ZH5TB5OdW4BVLm-1274216239894,1274538267659,
> responses,RS_3BHc4KyoM3q72Yc-1274290546987,1274502062319,
> responses,RS_3ra9BaBMAXFAvbK-127421457
> 9958,1274381552543, responses,RS_6SDrGNuyyLd3oR6-1274219941155,1274385453586,
> responses,RS_8AGCEMWbI6mZuoQ-1274306857429,1274319602718,
> responses,RS_8C8T9DN47uwTG1S-1274215381765,1274289112817,
> responses,RS_8J5wmdmKmJXzK6g-1274299593861,1274494738952,
> responses,RS_8e5Sz0HeFPAdb6c-1274288
> 641459,1274495868557,
> responses,RS_8rjcnmBXPKzI896-1274306981684,1274403047940,
> responses,RS_9FS3VedcyrF0KX2-1274245971331,1274754745013,
> responses,RS_9oZgPtxO31npv3C-1274214027769,1274396489756,
> responses,RS_a3FdO2jhqWuy37C-1274209228660,1274399508186,
> responses,RS_a3LJVxwTj29MHVa-12742
> {noformat}
> Then you see the too many log files:
> {noformat}
> 2010-05-25 10:53:31,364 DEBUG
> org.apache.hadoop.hbase.regionserver.CompactSplitThread: Compaction requested
> for region
> responses-index,--1274799047787--R_cBKrGxx0FdWjPso,1274804575862/783020138
> because: regionserver/192.168.0.81:60020.cacheFlusher
> 2010-05-25 10:53:32,364 WARN
> org.apache.hadoop.hbase.regionserver.MemStoreFlusher: Region
> responses-index,--1274799047787--R_cBKrGxx0FdWjPso,1274804575862 has too many
> store files, putting it back at the end of the flush queue.
> {noformat}
> Which leads to this:
> {noformat}
> 2010-05-25 10:53:27,061 INFO org.apache.hadoop.hbase.regionserver.HRegion:
> Blocking updates for 'IPC Server handler 60 on 60020' on region
> responses-index,--1274799047787--R_cBKrGxx0FdWjPso,1274804575862: memstore
> size 128.0m is >= than blocking 128.0m size
> 2010-05-25 10:53:27,061 INFO org.apache.hadoop.hbase.regionserver.HRegion:
> Blocking updates for 'IPC Server handler 84 on 60020' on region
> responses-index,--1274799047787--R_cBKrGxx0FdWjPso,1274804575862: memstore
> size 128.0m is >= than blocking 128.0m size
> 2010-05-25 10:53:27,065 INFO org.apache.hadoop.hbase.regionserver.HRegion:
> Blocking updates for 'IPC Server handler 1 on 60020' on region
> responses-index,--1274799047787--R_cBKrGxx0FdWjPso,1274804575862: memstore
> size 128.0m is >= than blocking 128.0m size
> {noformat}
> Once the compaction / split is done a flush is able to happen which unblocks
> the IPC allowing writes to continue. Unfortunately this process can take
> upwards of 15+ minutes (the specific case shown here from our logs took about
> 4 minutes).
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