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From "Miller, Austin" <Austin.Mil...@morganstanley.com>
Subject RE: <Unverified Sender>RE: exposing lastSend
Date Wed, 16 Jul 2014 18:36:18 GMT

I'm still hoping to spark some discussion about the last send value.

Given the links below...


It seems the issue of thread starvation has been considered previously and is considered sufficiently
important to possibly pursue a JNI solution.

While a JNI wrapper around a C client might increase the likelihood of ZooKeeper client threads
being scheduled in the OS, it does not completely ameliorate the issue.  Resource starvation,
memory, threads, and IO, may still prevent the client from being scheduled even in a C program.

It also adds new sources of failure, more complexity, and increases difficulty of deploying

There still seems to be a race condition, in the JNI solution, between session loss notification
and Java if a partition and pause happen simultaneously.

If it is assumed that long pauses happen for some users and the last send value is exposed,
then I maintain it is possible to use that value in ways that increase the chances that a
transaction is not committed when a session has been lost.  Some users may actually want failover
in the case of a really long pause in the JVM, as well.  From the cluster's point of view,
the app rebooted.

GC pauses are not the only things that cause resource starvation, either, and a cause agnostic
measure, like using the last send value to gate writes, is going to provide more confidence
than a JNI wrapper around C.



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