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Date: Sat, 9 Sep 2017 00:39:00 +0000 (UTC)
From: "xinxin fan (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-18090) Improve TableSnapshotInputFormat
 to allow more multiple mappers per region
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archived-at: Sat, 09 Sep 2017 00:39:10 -0000


    [ https://issues.apache.org/jira/browse/HBASE-18090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16159594#comment-16159594 ] 

xinxin fan commented on HBASE-18090:
------------------------------------

[[mailto:Mikhail Antonov]] Thanks for your review!

{quote}Before I go in reviews..opening regions in read-only mode for snapshots seems reasonable. That change would only affect MR over snapshots codebase or some other paths too?{quote}
I think the read-only regions only affect MR over snapshots codebase.

{quote} if we set readonly flag we skip replaying WAL and don't create those tmp files. {quote}
It seem that primary regions even opened in read only mode should replay the edits, just see HRegion.#initializeRegionInternals:

{code:java}
if (ServerRegionReplicaUtil.shouldReplayRecoveredEdits(this)) {
      // Recover any edits if available.
      maxSeqId = Math.max(maxSeqId,
        replayRecoveredEditsIfAny(this.fs.getRegionDir(), maxSeqIdInStores, reporter, status));
      // Make sure mvcc is up to max.
      this.mvcc.advanceTo(maxSeqId);
    }
{code}

{quote}Will that work for snapshots created with skipFlush option? Is it always safe to skip WAL in that case?{quote}
The MR just work on the snapshot store files, so i think it make no different if the region is read-only or not. How do you think?

> Improve TableSnapshotInputFormat to allow more multiple mappers per region
> --------------------------------------------------------------------------
>
>                 Key: HBASE-18090
>                 URL: https://issues.apache.org/jira/browse/HBASE-18090
>             Project: HBase
>          Issue Type: Improvement
>          Components: mapreduce
>    Affects Versions: 1.4.0
>            Reporter: Mikhail Antonov
>            Assignee: xinxin fan
>         Attachments: HBASE-18090-branch-1.3-v1.patch, HBASE-18090-branch-1.3-v2.patch
>
>
> TableSnapshotInputFormat runs one map task per region in the table snapshot. This places unnecessary restriction that the region layout of the original table needs to take the processing resources available to MR job into consideration. Allowing to run multiple mappers per region (assuming reasonably even key distribution) would be useful.


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