[jira] [Commented] (PHOENIX-5604) Index rebuilds and read repairs should not skip WAL

["Kadir OZDEMIR (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PHOENIX-5604?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16989083#comment-16989083 ] 

Kadir OZDEMIR commented on PHOENIX-5604:
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[~gjacoby], I was not sure if the mutation attribute for durability is limited to the data mutations or it is also propagated to the index mutations too. Have you verified this? 

Your statement " but if the repair action – whether a put or delete – doesn't go into the WAL, a DR buddy of the index will be out of sync"  is not accurate. Any read at the DR side will trigger read repair as it does at the source.

> Index rebuilds and read repairs should not skip WAL
> ---------------------------------------------------
>
>                 Key: PHOENIX-5604
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-5604
>             Project: Phoenix
>          Issue Type: Bug
>            Reporter: Geoffrey Jacoby
>            Assignee: Geoffrey Jacoby
>            Priority: Major
>         Attachments: PHOENIX-5604-4.x-HBase-1.5.patch
>
>
> Currently both Index read repairs and IndexTool build/rebuilds in the new design continue to skip the WAL, following the same pattern the old Indexer used. However, there are key differences between the old and new logic that make this no longer the correct choice.
> First, recall that all HBase replication is based on tailing the WAL, and that any transaction that skips the WAL doesn't get replicated. 
> In the old logic, the data table write (and WAL append) would be accompanied by an IndexedKeyValue which would contain enough information to reconstitute the index edit in the event of a failure before the index edit could be committed. So skipping the WAL during recovery was _potentially_ OK, because writing to the WAL would be redundant locally. (But that still seems to me wrong in a case with replication, since I don't believe IndexedKeyValues are replicated, since they use the "magic" METAFAMILY cf.)  
> In the new logic, on a normal write, we write to the index first (which will go into a WAL), then the data table (into a potentially different RS's WAL), and lastly the verified flag flip into the Index, into the original index write's WAL. If something goes wrong with stage 2 or 3, read repair will fix it, but if the repair action – whether a put or delete – doesn't go into the WAL, a DR buddy of the index will be out of sync. 
> This is even more important on an async initial build of an index, where if I understand right, there is no WAL append for the index write at all in the current UngroupedAggregateRegionObserver rebuild logic. The same would be the case of a rebuild of a new-style index in the event of non-Phoenix related corruption (such as HDFS or raw HBase level). 



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