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https://issues.apache.org/jira/browse/HBASE-20090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16397086#comment-16397086
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Eshcar Hillel commented on HBASE-20090:
---------------------------------------

yes to this set

> Properly handle Preconditions check failure in 
> MemStoreFlusher$FlushHandler.run
> -------------------------------------------------------------------------------
>
>                 Key: HBASE-20090
>                 URL: https://issues.apache.org/jira/browse/HBASE-20090
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Ted Yu
>            Assignee: Ted Yu
>            Priority: Major
>         Attachments: 20090-server-61260-01-000007.log, 20090.v6.txt, 
> 20090.v7.txt
>
>
> Copied the following from a comment since this was better description of the 
> race condition.
> The original description was merged to the beginning of my first comment 
> below.
> With more debug logging, we can see the scenario where the exception was 
> triggered.
> {code}
> 2018-03-02 17:28:30,097 DEBUG [MemStoreFlusher.0] regionserver.CompactSplit: 
> Splitting TestTable,,1520011528142.0453f29030757eedb6e6a1c57e88c085., 
> compaction_queue=(0:0),     split_queue=1
> 2018-03-02 17:28:30,098 DEBUG 
> [RpcServer.priority.FPBQ.Fifo.handler=19,queue=1,port=16020] 
> regionserver.IncreasingToUpperBoundRegionSplitPolicy: ShouldSplit because 
> info      size=6.9G, sizeToCheck=256.0M, regionsWithCommonTable=1
> 2018-03-02 17:28:30,296 INFO  
> [RpcServer.default.FPBQ.Fifo.handler=24,queue=0,port=16020] 
> regionserver.MemStoreFlusher: wake up flusher due to ABOVE_ONHEAP_LOWER_MARK
> 2018-03-02 17:28:30,297 DEBUG [MemStoreFlusher.1] 
> regionserver.MemStoreFlusher: Flush thread woke up because memory above low 
> water=381.5 M
> 2018-03-02 17:28:30,297 INFO  
> [RpcServer.default.FPBQ.Fifo.handler=25,queue=1,port=16020] 
> regionserver.MemStoreFlusher: wake up flusher due to ABOVE_ONHEAP_LOWER_MARK
> 2018-03-02 17:28:30,298 DEBUG [MemStoreFlusher.1] 
> regionserver.MemStoreFlusher: region 
> TestTable,,1520011528142.0453f29030757eedb6e6a1c57e88c085. with size 400432696
> 2018-03-02 17:28:30,298 DEBUG [MemStoreFlusher.1] 
> regionserver.MemStoreFlusher: region 
> atlas_janus,,1519927429371.fbcb5e495344542daf8b499e4bac03ae. with size 0
> 2018-03-02 17:28:30,298 INFO  [MemStoreFlusher.1] 
> regionserver.MemStoreFlusher: Flush of region 
> atlas_janus,,1519927429371.fbcb5e495344542daf8b499e4bac03ae. due to global    
>  heap pressure. Flush type=ABOVE_ONHEAP_LOWER_MARKTotal Memstore Heap 
> size=381.9 MTotal Memstore Off-Heap size=0, Region memstore size=0
> 2018-03-02 17:28:30,298 INFO  [MemStoreFlusher.1] 
> regionserver.MemStoreFlusher: wake up by WAKEUPFLUSH_INSTANCE
> 2018-03-02 17:28:30,298 INFO  [MemStoreFlusher.1] 
> regionserver.MemStoreFlusher: Nothing to flush for 
> atlas_janus,,1519927429371.fbcb5e495344542daf8b499e4bac03ae.
> 2018-03-02 17:28:30,298 INFO  [MemStoreFlusher.1] 
> regionserver.MemStoreFlusher: Excluding unflushable region 
> atlas_janus,,1519927429371.fbcb5e495344542daf8b499e4bac03ae. -    trying to 
> find a different region to flush.
> {code}
> Region 0453f29030757eedb6e6a1c57e88c085 was being split.
> In HRegion#flushcache, the log from else branch can be seen in 
> 20090-server-61260-01-000007.log :
> {code}
>       synchronized (writestate) {
>         if (!writestate.flushing && writestate.writesEnabled) {
>           this.writestate.flushing = true;
>         } else {
>           if (LOG.isDebugEnabled()) {
>             LOG.debug("NOT flushing memstore for region " + this
>                 + ", flushing=" + writestate.flushing + ", writesEnabled="
>                 + writestate.writesEnabled);
>           }
> {code}
> Meaning, region 0453f29030757eedb6e6a1c57e88c085 couldn't flush, leaving 
> memory pressure at high level.
> When MemStoreFlusher ran to the following call, the region was no longer a 
> flush candidate:
> {code}
>       HRegion bestFlushableRegion =
>           getBiggestMemStoreRegion(regionsBySize, excludedRegions, true);
> {code}
> So the other region, 
> atlas_janus,,1519927429371.fbcb5e495344542daf8b499e4bac03ae. , was examined 
> next. Since the region was not receiving write, the (current) Precondition 
> check failed.
> The proposed fix is to convert the Precondition to normal return.



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