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From Todd Lipcon <t...@cloudera.com>
Subject Re: Question about redistributing tablets on failure of a tserver.
Date Mon, 08 May 2017 19:55:21 GMT
Hey Jason

Sorry for the delayed response here. It looks from your ksck like copying
is ongoing but hasn't yet finished.

FWIW Will B is working on adding more informative output to ksck to help
diagnose cases like this:
https://gerrit.cloudera.org/#/c/6772/

-Todd

On Thu, Apr 13, 2017 at 11:35 PM, Jason Heo <jason.heo.sde@gmail.com> wrote:

> @Dan
>
> I monitored with `kudu ksck` while re-replication is occurring, but I'm
> not sure if this output means my cluster has a problem. (It seems just
> indicating one tserver stopped)
>
> Would you please check it?
>
> Thank,
>
> Jason
>
> ```
> ...
> ...
> Tablet 0e29XXXXXXXXXXXXXXX1e1e3168a4d81 of table 'impala::tbl1' is
> under-replicated: 1 replica(s) not RUNNING
>   a7ca07f9bXXXXXXXXXXXXXXXbbb21cfb (hostname.com:7050): RUNNING
>   a97644XXXXXXXXXXXXXXXdb074d4380f (hostname.com:7050): RUNNING [LEADER]
>   401b6XXXXXXXXXXXXXXX5feda1de212b (hostname.com:7050): missing
>
> Tablet 550XXXXXXXXXXXXXXX08f5fc94126927 of table 'impala::tbl1' is
> under-replicated: 1 replica(s) not RUNNING
>   aec55b4XXXXXXXXXXXXXXXdb469427cf (hostname.com:7050): RUNNING [LEADER]
>   a7ca07f9b3d94XXXXXXXXXXXXXXX1cfb (hostname.com:7050): RUNNING
>   31461XXXXXXXXXXXXXXX3dbe060807a6 (hostname.com:7050): bad state
>     State:       NOT_STARTED
>     Data state:  TABLET_DATA_READY
>     Last status: Tablet initializing...
>
> Tablet 4a1490fcXXXXXXXXXXXXXXX7a2c637e3 of table 'impala::tbl1' is
> under-replicated: 1 replica(s) not RUNNING
>   a7ca07f9b3d94414XXXXXXXXXXXXXXXb (hostname.com:7050): RUNNING
>   40XXXXXXXXXXXXXXXd5b5feda1de212b (hostname.com:7050): RUNNING [LEADER]
>   aec55b4e2acXXXXXXXXXXXXXXX9427cf (hostname.com:7050): bad state
>     State:       NOT_STARTED
>     Data state:  TABLET_DATA_COPYING
>     Last status: TabletCopy: Downloading block 0000000005162382 (277/581)
> ...
> ...
> ==================
> Errors:
> ==================
> table consistency check error: Corruption: 52 table(s) are bad
>
> FAILED
> Runtime error: ksck discovered errors
> ```
>
>
>
> 2017-04-13 3:47 GMT+09:00 Dan Burkert <danburkert@apache.org>:
>
>> Hi Jason, answers inline:
>>
>> On Wed, Apr 12, 2017 at 5:53 AM, Jason Heo <jason.heo.sde@gmail.com>
>> wrote:
>>
>>>
>>> Q1. Can I disable redistributing tablets on failure of a tserver? The
>>> reason why I need this is described in Background.
>>>
>>
>> We don't have any kind of built-in maintenance mode that would prevent
>> this, but it can be achieved by setting a flag on each of the tablet
>> servers.  The goal is not to disable re-replicating tablets, but instead to
>> avoid kicking the failed replica out of the tablet groups to begin with.
>> There is a config flag to control exactly that: 'evict_failed_followers'.
>> This isn't considered a stable or supported flag, but it should have the
>> effect you are looking for, if you set it to false on each of the tablet
>> servers, by running:
>>
>>     kudu tserver set-flag <tserver-addr> evict_failed_followers false
>> --force
>>
>> for each tablet server.  When you are done, set it back to the default
>> 'true' value.  This isn't something we routinely test (especially setting
>> it without restarting the server), so please test before trying this on a
>> production cluster.
>>
>> Q2. redistribution goes on even if the failed tserver reconnected to
>>> cluster. In my test cluster, it took 2 hours to distribute when a tserver
>>> which has 3TB data was killed.
>>>
>>
>> This seems slow.  What's the speed of your network?  How many nodes?  How
>> many tablet replicas were on the failed tserver, and were the replica sizes
>> evenly balanced?  Next time this happens, you might try monitoring with
>> 'kudu ksck' to ensure there aren't additional problems in the cluster (admin guide
>> on the ksck tool
>> <https://github.com/apache/kudu/blob/master/docs/administration.adoc#ksck>
>> ).
>>
>>
>>> Q3. `--follower_unavailable_considered_failed_sec` can be changed
>>> without restarting cluster?
>>>
>>
>> The flag can be changed, but it comes with the same caveats as above:
>>
>>     'kudu tserver set-flag <tserver-addr> follower_unavailable_considered_failed_sec
>> 900 --force'
>>
>>
>> - Dan
>>
>>
>


-- 
Todd Lipcon
Software Engineer, Cloudera

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