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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-10924) [region_mover]: Adjust region_mover script to retry unloading a server a configurable number of times in case of region splits/merges
Date Sun, 27 Jul 2014 18:57:39 GMT

     [ https://issues.apache.org/jira/browse/HBASE-10924?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Lars Hofhansl updated HBASE-10924:

    Fix Version/s:     (was: 0.94.22)

> [region_mover]: Adjust region_mover script to retry unloading a server a configurable
number of times in case of region splits/merges
> -------------------------------------------------------------------------------------------------------------------------------------
>                 Key: HBASE-10924
>                 URL: https://issues.apache.org/jira/browse/HBASE-10924
>             Project: HBase
>          Issue Type: Bug
>          Components: Region Assignment
>    Affects Versions: 0.94.15
>            Reporter: Aleksandr Shulman
>            Assignee: Aleksandr Shulman
>              Labels: region_mover, rolling_upgrade
>             Fix For: 0.94.23
>         Attachments: HBASE-10924-0.94-v2.patch, HBASE-10924-0.94-v3.patch
> Observed behavior:
> In about 5% of cases, my rolling upgrade tests fail because of stuck regions during a
region server unload. My theory is that this occurs when region assignment information changes
between the time the region list is generated, and the time when the region is to be moved.
> An example of such a region information change is a split or merge.
> Example:
> Regionserver A has 100 regions (#0-#99). The balancer is turned off and the regionmover
script is called to unload this regionserver. The regionmover script will generate the list
of 100 regions to be moved and then proceed down that list, moving the regions off in series.
However, there is a region, #84, that has split into two daughter regions while regions 0-83
were moved. The script will be stuck trying to move #84, timeout, and then the failure will
bubble up (attempt 1 failed).
> Proposed solution:
> This specific failure mode should be caught and the region_mover script should now attempt
to move off all the regions. Now, it will have 16+1 (due to split) regions to move. There
is a good chance that it will be able to move all 17 off without issues. However, should it
encounter this same issue (attempt 2 failed), it will retry again. This process will continue
until the maximum number of unload retry attempts has been reached.
> This is not foolproof, but let's say for the sake of argument that 5% of unload attempts
hit this issue, then with a retry count of 3, it will reduce the unload failure probability
from 0.05 to 0.000125 (0.05^3).
> Next steps:
> I am looking for feedback on this approach. If it seems like a sensible approach, I will
create a strawman patch and test it.

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