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https://issues.apache.org/jira/browse/ZOOKEEPER-1148?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13087907#comment-13087907
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Vishal Kathuria commented on ZOOKEEPER-1148:
--------------------------------------------
Thanks for taking a look at the patch Patrick. I deliberately did not click
"submit patch" since it was not ready to be committed :)
I will be breaking this up into smaller committable chunks and submitting those
patches over the next few weeks.
thanks!
> Multi-threaded handling of reads
> ---------------------------------
>
> Key: ZOOKEEPER-1148
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1148
> Project: ZooKeeper
> Issue Type: Improvement
> Components: server
> Reporter: Vishal Kathuria
> Labels: scaling
> Fix For: 3.5.0
>
> Attachments: zookeeperEverything.patch
>
>
> This improvement is to take advantage of multiple cores in the machines that
> typically run ZooKeeper servers to get higher read throughput.
> The challenge with multiple threads is read/write ordering guarantees that
> ZooKeeper provides.
> One way of handling these is to let readOnly clients use the multiple
> threads, and the read/write clients continue to use the same single
> CommitProcessor thread for both reads and writes. For this to work, a client
> would have to declare its readOnly intent through a flag at connect time. (We
> already have a readOnly flag, but its intent is a bit different).
> Another way of honoring the read/write guarantee is to let all sessions start
> as readOnly sessions and have them use the multi-threaded reads until they do
> their first write. Once a session performs a write, it automatically flips
> from a read/write session to a read only session and starts using the single
> threaded CommitProcessor. This is a little tricky as one has to worry about
> in flight reads when the write comes and we have to make sure those reads
> finish before the write goes through.
> I would like to get the community's feedback on whether it would be useful to
> have this and whether an automatic discovery of readOnly or read/write intent
> is critical for this to be useful. For us, the clients know at connect time
> whether they will ever do a write or not, so an automatic detection is of
> limited use.
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