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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-16162) Unnecessary push active segments to pipeline
Date Fri, 01 Jul 2016 11:46:10 GMT

    [ https://issues.apache.org/jira/browse/HBASE-16162?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15358839#comment-15358839
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ramkrishna.s.vasudevan commented on HBASE-16162:
------------------------------------------------

I think this even fixes many of the problems  because under heavy load the number of items
in pipeline is around 40 sometimes and hence multiple threads producing big pipelines is a
load on the heap and thus leading to big GCs. 


> Unnecessary push active segments to pipeline
> --------------------------------------------
>
>                 Key: HBASE-16162
>                 URL: https://issues.apache.org/jira/browse/HBASE-16162
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Anoop Sam John
>            Assignee: Anoop Sam John
>
> We have flow like this
> {code}
> protected void checkActiveSize() {
>     if (shouldFlushInMemory()) {
>          InMemoryFlushRunnable runnable = new InMemoryFlushRunnable();
>       }
>       getPool().execute(runnable);
>     }
>   }
> private boolean shouldFlushInMemory() {
>     if(getActive().getSize() > inmemoryFlushSize) {
>       // size above flush threshold
>       return (allowCompaction.get() && !inMemoryFlushInProgress.get());
>     }
>     return false;
>   }
> void flushInMemory() throws IOException {
>     // Phase I: Update the pipeline
>     getRegionServices().blockUpdates();
>     try {
>       MutableSegment active = getActive();
>       pushActiveToPipeline(active);
>     } finally {
>       getRegionServices().unblockUpdates();
>     }
>     // Phase II: Compact the pipeline
>     try {
>       if (allowCompaction.get() && inMemoryFlushInProgress.compareAndSet(false,
true)) {
>         // setting the inMemoryFlushInProgress flag again for the case this method is
invoked
>         // directly (only in tests) in the common path setting from true to true is idempotent
>         // Speculative compaction execution, may be interrupted if flush is forced while
>         // compaction is in progress
>         compactor.startCompaction();
>       }
> {code}
> So every write of cell will produce the check checkActiveSize().   When we are at border
of in mem flush,  many threads doing writes to this memstore can get this check to pass. 
Yes the AtomicBoolean is still false only. It is turned ON after some time once the new thread
is started run and it push the active to pipeline etc.
> The time gap btw the size check return true and the block updates.   In btw all updates
to memstore would have kicked this in memory flush
> So all these threads can push the same active to pipeline.  We unnecessarily passing
through same segment many times. 



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