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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3065) Retry all 'retryable' zk operations; e.g. connection loss
Date Fri, 29 Jul 2011 16:12:09 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13072886#comment-13072886
] 

stack commented on HBASE-3065:
------------------------------

Excellent Ram.  I'd figured the first part of your patch last night -- the metdata prefix
-- but not the second.  Thank you.  Let me build on your patch for the rest of the fix.

So, yes, distributed log splitting does heavy interactions with zk.  It went in after the
original 3065 patch was done.  The url encoding that distributed splitting zk'ing does is
clashing with suffixes that this patch adds to file names -- we need to find the places where
we want to use znode name and make sure we url decode.  The second issue is the one you note
above where this patch adds metadata at front of data and we need to strip it reading in a
few places.

Let me see how far I get today (I'm gone for a week starting this evening...)

> Retry all 'retryable' zk operations; e.g. connection loss
> ---------------------------------------------------------
>
>                 Key: HBASE-3065
>                 URL: https://issues.apache.org/jira/browse/HBASE-3065
>             Project: HBase
>          Issue Type: Bug
>            Reporter: stack
>            Assignee: Liyin Tang
>            Priority: Critical
>             Fix For: 0.92.0
>
>         Attachments: 3065-v3.txt, 3065-v4.txt, HBASE-3065-addendum.patch, HBase-3065[r1088475]_1.patch,
hbase3065_2.patch
>
>
> The 'new' master refactored our zk code tidying up all zk accesses and coralling them
behind nice zk utility classes.  One improvement was letting out all KeeperExceptions letting
the client deal.  Thats good generally because in old days, we'd suppress important state
zk changes in state.  But there is at least one case the new zk utility could handle for the
application and thats the class of retryable KeeperExceptions.  The one that comes to mind
is conection loss.  On connection loss we should retry the just-failed operation.  Usually
the retry will just work.  At worse, on reconnect, we'll pick up the expired session event.

> Adding in this change shouldn't be too bad given the refactor of zk corralled all zk
access into one or two classes only.
> One thing to consider though is how much we should retry.  We could retry on a timer
or we could retry for ever as long as the Stoppable interface is passed so if another thread
has stopped or aborted the hosting service, we'll notice and give up trying.  Doing the latter
is probably better than some kinda timeout.
> HBASE-3062 adds a timed retry on the first zk operation.  This issue is about generalizing
what is over there across all zk access.

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