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Date: Mon, 22 May 2017 11:05:04 +0000 (UTC)
From: "Jingyun Tian (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.13072457.1494943215000.261981.1495451104317@Atlassian.JIRA>
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Subject: [jira] [Commented] (HBASE-18059) The scanner order for memstore
 scanners are wrong
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archived-at: Mon, 22 May 2017 11:05:09 -0000


    [ https://issues.apache.org/jira/browse/HBASE-18059?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16019453#comment-16019453 ] 

Jingyun Tian commented on HBASE-18059:
--------------------------------------

[~appy] since every cell in memstore has a sequence ID, I think the problem that memstore has the same scanner order with storefile makes the order wrong seems cannot happen. Because the CellComparator will consider the sequence ID before scanner order, so I think the comparison of scanner order will not happen. 
In addition, is there a situation that data from bulk import could have same sequence ID with cells in memstore?  

> The scanner order for memstore scanners are wrong
> -------------------------------------------------
>
>                 Key: HBASE-18059
>                 URL: https://issues.apache.org/jira/browse/HBASE-18059
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver, scan, Scanners
>    Affects Versions: 2.0.0
>            Reporter: Duo Zhang
>            Assignee: Jingyun Tian
>             Fix For: 2.0.0
>
>
> This is comments for KeyValueScanner.getScannerOrder
> {code:title=KeyValueScanner.java}
>   /**
>    * Get the order of this KeyValueScanner. This is only relevant for StoreFileScanners and
>    * MemStoreScanners (other scanners simply return 0). This is required for comparing multiple
>    * files to find out which one has the latest data. StoreFileScanners are ordered from 0
>    * (oldest) to newest in increasing order. MemStoreScanner gets LONG.max since it always
>    * contains freshest data.
>    */
>   long getScannerOrder();
> {code}
> As now we may have multiple memstore scanners, I think the right way to select scanner order for memstore scanner is to ordered from Long.MAX_VALUE in decreasing order.
> But in CompactingMemStore and DefaultMemStore, the scanner order for memstore scanner is also start from 0, which will be messed up with StoreFileScanners.


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