[jira] [Updated] (ACCUMULO-2819) Provide WorkAssigner which is order-aware

["Josh Elser (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ACCUMULO-2819?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Josh Elser updated ACCUMULO-2819:
---------------------------------
    Fix Version/s: 1.7.0

> Provide WorkAssigner which is order-aware
> -----------------------------------------
>
>                 Key: ACCUMULO-2819
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2819
>             Project: Accumulo
>          Issue Type: Sub-task
>          Components: replication
>            Reporter: Josh Elser
>            Assignee: Josh Elser
>             Fix For: 1.7.0
>
>
> The current WorkAssigner implementation, which uses the DistributedWorkQueue, is great because it allows the Master to be unaware of what tservers are available, and to allow any tserver to perform the replication.
> The downside of this is that it is possible to replicate data that was ingested later before the earlier ingested data. For example, say {{table1}} uses {{wal1}} to ingest some data. We record that {{wal1}} has some replication to do, but, for whatever reason, we don't get to it. More data is ingested into {{table1}}, and it starts using {{wal2}} after enough data was ingested. Now, we have {{wal1}} and {{wal2}} which both have data to be replicated for {{table1}}.
> Using the DistributedWorkQueue, we have no guarantee that {{wal1}} will be replicated before {{wal2}}, which means we might replay a column update for the same row in the wrong order (update from {{wal2}} and then update from {{wal1}}).
> While the DistributedWorkQueue is nice for the mentioned reason, in addition to the higher throughput, it has obvious deficiencies depending on the workload and table schema. We need to create a WorkAssigner that is order aware (what was the order in which the WALs for a table were minor compacted, and ensure that replication occurs in that same order.



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