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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-18116) Replication buffer quota accounting should not include bulk transfer hfiles
Date Thu, 25 May 2017 18:22:04 GMT
Andrew Purtell created HBASE-18116:
--------------------------------------

             Summary: Replication buffer quota accounting should not include bulk transfer
hfiles
                 Key: HBASE-18116
                 URL: https://issues.apache.org/jira/browse/HBASE-18116
             Project: HBase
          Issue Type: Bug
          Components: Replication
            Reporter: Andrew Purtell


In ReplicationSourceWALReaderThread we maintain a global quota on enqueued replication work
for preventing OOM by queuing up too many edits into queues on heap. When calculating the
size of a given replication queue entry, if it has associated hfiles (is a bulk load to be
replicated as a batch of hfiles), we get the file sizes and include the sum. We then apply
that result to the quota. This isn't quite right. Those hfiles will be transferred by the
sink as a file copy and then the files will be bulk loaded on the sink. The cells in those
files are not queued in memory at the source and therefore shouldn't be counted against the
quota.

Related, the sum of the hfile sizes are also included when checking if queued work exceeds
the configured replication queue capacity, which is by default 64 MB. HFiles are commonly
much larger than this. 

So what happens is when we encounter a bulk load replication entry typically both the quota
and capacity limits are exceeded, we break out of loops, and send right away. What is transferred
on the wire via HBase RPC though has only a partial relationship to the calculation. 

Depending how you look at it, it makes sense to factor hfile file sizes against replication
queue capacity limits. The sink will be occupied transferring those files at the HDFS level.
Anyway, this is how we have been doing it and it is too late to change now. I do not however
think it is correct to apply hfile file sizes against a quota for in memory state on the source.
The source doesn't queue or even transfer those bytes. 

Something I noticed while working on HBASE-18027.



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