[jira] [Comment Edited] (HBASE-13378) RegionScannerImpl synchronized for READ_UNCOMMITTED Isolation Levels

["Andrew Purtell (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-13378?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14579309#comment-14579309 ] 

Andrew Purtell edited comment on HBASE-13378 at 6/9/15 5:53 PM:
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{quote}
bq. Up to this point READ_UNCOMMITED meant: You might see partially finished rows.
bq. Now it means: You might see partially finished rows, and you may not see cells that have existed when the scanner started.
This sounds to me like an incompatible change for a patch release
{quote}

Precisely, why does this sound like an *incompatible* change?


was (Author: apurtell):
{quote}
bq. Up to this point READ_UNCOMMITED meant: You might see partially finished rows.
Now it means: You might see partially finished rows, and you may not see cells that have existed when the scanner started.
This sounds to me like an incompatible change for a patch release
{quote}

Precisely, why does this sound like an *incompatible* change?

> RegionScannerImpl synchronized for READ_UNCOMMITTED Isolation Levels
> --------------------------------------------------------------------
>
>                 Key: HBASE-13378
>                 URL: https://issues.apache.org/jira/browse/HBASE-13378
>             Project: HBase
>          Issue Type: New Feature
>            Reporter: John Leach
>            Assignee: John Leach
>            Priority: Minor
>         Attachments: HBASE-13378.patch, HBASE-13378.txt
>
>   Original Estimate: 2h
>          Time Spent: 2h
>  Remaining Estimate: 0h
>
> This block of code below coupled with the close method could be changed so that READ_UNCOMMITTED does not synchronize.  
> {CODE:JAVA}
>       // synchronize on scannerReadPoints so that nobody calculates
>       // getSmallestReadPoint, before scannerReadPoints is updated.
>       IsolationLevel isolationLevel = scan.getIsolationLevel();
>       synchronized(scannerReadPoints) {
>         this.readPt = getReadpoint(isolationLevel);
>         scannerReadPoints.put(this, this.readPt);
>       }
> {CODE}
> This hotspots for me under heavy get requests.



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