[jira] [Commented] (HBASE-18059) The scanner order for memstore scanners are wrong

["Jingyun Tian (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-18059?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16441839#comment-16441839 ] 

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

IMO the scanner order for memstore is actually useless. I removed all code of scanner order in memstore related classes. This patch passed test at my local PC.

> 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
>            Priority: Critical
>             Fix For: 2.0.0
>
>         Attachments: HBASE-18059.master.001.patch
>
>
> 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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