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https://issues.apache.org/jira/browse/ACCUMULO-2931?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Josh Elser updated ACCUMULO-2931:
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Assignee: (was: Josh Elser)
> Ensure correct ordering of updates to a tablet across different WALs
> --------------------------------------------------------------------
>
> Key: ACCUMULO-2931
> URL: https://issues.apache.org/jira/browse/ACCUMULO-2931
> Project: Accumulo
> Issue Type: Bug
> Components: replication
> Reporter: Josh Elser
> Priority: Minor
>
> I was talking to [~enis] today about common replication problems across HBase
> and Accumulo and he was telling me about the following:
> A tablet is hosted by tserver1 using WAL1. That tablet moves to a different
> tserver for whatever reason (tserver1 failed, the balancer, etc) and starts
> getting used by tserver2 with WAL2.
> In the simple case of replicating to another Accumulo instance with servers
> running NTP, this shouldn't be a big concern because the timestamp assigned
> to the updates will ensure a final consistent view. However, the intermediate
> view is incorrect. We can do a better job to ensure that we replicate the
> data in the correct order.
> We already know the WALs that are used by a tablet and the time in which that
> tablet began using it (done by the TabletServer before any updates hit that
> Tablet) in the metadata table. We can use these records, in addition to the
> timestamp on the {{log}} column entries to determine the correct ordering for
> this Tablet WRT to all WALs. All the information is present so that the
> Master can assign the replication work in the correct order.
> Some extra bookkeeping would also be required to either keep that {{log}}
> column around longer than the minc or recovery, or to record some additional
> piece of replication metadata that the master can read from the replication
> table.
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