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From "Keith Turner (Commented) (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-444) Data loss possible when tablet killed immediately after recovery
Date Mon, 05 Mar 2012 23:13:58 GMT


Keith Turner commented on ACCUMULO-444:

I think ACCUMULO-388 would have made this bug show up sooner in testing.  
> Data loss possible when tablet killed immediately after recovery
> ----------------------------------------------------------------
>                 Key: ACCUMULO-444
>                 URL:
>             Project: Accumulo
>          Issue Type: Bug
>          Components: tserver
>    Affects Versions: 1.3.5
>         Environment: Running random walk, continuous ingest, and agitator on 10 node
>            Reporter: Keith Turner
>            Assignee: Keith Turner
>            Priority: Blocker
>             Fix For: 1.4.0, 1.3.6
> Came in after a weekend of running test to find the Shard random walk test had lost data
in its index table.  After debugging I found the following sequence of events occurred.
>  * Mutation X was written to shard index on Tablet T1
>  * X was minor compacted to file F1
>  * Tablet server serving T1 was killed
>  * When T1 came up on another tablet server, it did not know about F1
> The above sequence of events indicate that the !METADATA table lost data.  So I started
looking into that, and found the following sequence of events.
>  * Tablet server T1 serving METADATA tablet MT was killed
>  * MT comes up on another tablet server T2
>  * Mutation Y is written to MT about file F1 for tablet T1
>  * Tablet server T2 is killed.
>  * MT comes up in tablet server T3
>  * The mutations for MT from T1 are recovered, but not from T2.. therefore Y is lost
> There is code that supposed to handle this situation, but its not working... I think
this issue exist in 1.3
> Data loss is not certain in this situation.  In the scenario above, when MT is loaded
on T2 a minor compaction is started.  If the server is killed before this minor compaction
completes then data loss will likely occur.

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