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From "Jimmy Xiang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5162) Basic client pushback mechanism
Date Tue, 23 Oct 2012 22:42:12 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5162?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13482767#comment-13482767
] 

Jimmy Xiang commented on HBASE-5162:
------------------------------------

Isn't the exception way much cleaner and simpler?  I think the exception way is greedy, and
the hbase client code needs minimal change. Based on the retry count, it can adjust the delay
time in the middle.

For the load monitoring, we assume the load trend remains the same, which may not be that
case actually. The client side has to track the regions whose memstore is under pressure.
 Every client needs to do the same tracking.
                
> Basic client pushback mechanism
> -------------------------------
>
>                 Key: HBASE-5162
>                 URL: https://issues.apache.org/jira/browse/HBASE-5162
>             Project: HBase
>          Issue Type: New Feature
>    Affects Versions: 0.92.0
>            Reporter: Jean-Daniel Cryans
>             Fix For: 0.96.0
>
>         Attachments: java_HBASE-5162.patch
>
>
> The current blocking we do when we are close to some limits (memstores over the multiplier
factor, too many store files, global memstore memory) is bad, too coarse and confusing. After
hitting HBASE-5161, it really becomes obvious that we need something better.
> I did a little brainstorm with Stack, we came up quickly with two solutions:
>  - Send some exception to the client, like OverloadedException, that's thrown when some
situation happens like getting past the low memory barrier. It would be thrown when the client
gets a handler and does some check while putting or deleting. The client would treat this
a retryable exception but ideally wouldn't check .META. for a new location. It could be fancy
and have multiple levels of pushback, like send the exception to 25% of the clients, and then
go up if the situation persists. Should be "easy" to implement but we'll be using a lot more
IO to send the payload over and over again (but at least it wouldn't sit in the RS's memory).
>  - Send a message alongside a successful put or delete to tell the client to slow down
a little, this way we don't have to do back and forth with the payload between the client
and the server. It's a cleaner (I think) but more involved solution.
> In every case the RS should do very obvious things to notify the operators of this situation,
through logs, web UI, metrics, etc.
> Other ideas?

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