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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6752) On region server failure, serve writes and timeranged reads during the log split
Date Mon, 10 Sep 2012 21:37:07 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6752?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452467#comment-13452467
] 

stack commented on HBASE-6752:
------------------------------

bq. specific exception returned to the client when we cannot server.

Who would return this?  Not the server that just failed?

Or is it during recovery?  The region will be assigned this new location and meta gets updated
w/ new location only the region is not fully on line because its still recovering?

Or is this when region is moved?

bq. Priority is given to region server holding the new regions

What does this mean?  What kinda of priority?

I like being able to take writes the sooner.
                
> On region server failure, serve writes and timeranged reads during the log split
> --------------------------------------------------------------------------------
>
>                 Key: HBASE-6752
>                 URL: https://issues.apache.org/jira/browse/HBASE-6752
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>    Affects Versions: 0.96.0
>            Reporter: nkeywal
>            Priority: Minor
>
> Opening for write on failure would mean:
> - Assign the region to a new regionserver. It marks the region as recovering
>   -- specific exception returned to the client when we cannot server.
>   -- allow them to know where they stand. The exception can include some time information
(failure stated on: ...)
>   -- allow them to go immediately on the right regionserver, instead of retrying or calling
the region holding meta to get the new address
>      => save network calls, lower the load on meta.
> - Do the split as today. Priority is given to region server holding the new regions
>   -- help to share the load balancing code: the split is done by region server considered
as available for new regions
>   -- help locality (the recovered edits are available on the region server) => lower
the network usage
> - When the split is finished, we're done as of today
> - while the split is progressing, the region server can
>  -- serve writes
>    --- that's useful for all application that need to write but not read immediately:
>    --- whatever logs events to analyze them later
>    --- opentsdb is a perfect example.   
>  -- serve reads if they have a compatible time range. For heavily used tables, it could
be an help, because:
>    --- we can expect to have a few minutes of data only (as it's loaded)
>    --- the heaviest queries, often accepts a few -or more- minutes delay. 
> Some "What if":
> 1) the split fails
> => Retry until it works. As today. Just that we serves writes. We need to know (as
today) that the region has not recovered if we fail again.
> 2) the regionserver fails during the split
> => As 1 and as of today/
> 3) the regionserver fails after the split but before the state change to fully available.
> => New assign. More logs to split (the ones already dones and the new ones).
> 4) the assignment fails
> => Retry until it works. As today.

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