[jira] [Resolved] (HBASE-29039) Optimize read performance for accumulated delete markers on the same row or cell

["Junegunn Choi (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-29039?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Junegunn Choi resolved HBASE-29039.
-----------------------------------
    Fix Version/s: 2.7.0
                   3.0.0-beta-2
                   2.5.15
                   2.6.6
       Resolution: Fixed

Thank you [~Eungsop Yoo] for reporting the issue and providing a patch.

[PR #8001|https://github.com/apache/hbase/pull/8001] has been merged, and backported to the following branches:

* branch-3
* branch-2
* branch-2.6
* branch-2.5

Thanks to [~cconnell] for the review!


> Optimize read performance for accumulated delete markers on the same row or cell
> --------------------------------------------------------------------------------
>
>                 Key: HBASE-29039
>                 URL: https://issues.apache.org/jira/browse/HBASE-29039
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 2.6.1, 2.5.10
>            Reporter: Eungsop Yoo
>            Assignee: Junegunn Choi
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 2.7.0, 3.0.0-beta-2, 2.5.15, 2.6.6
>
>         Attachments: screenshot-2.png
>
>
> I have been confronted with a problem that some Get operations take several seconds. 
> !screenshot-2.png!
> The reason was founded that users Put and Delete on some rows repeatedly. As delete markers are accumulated on the same row or cell, Get operations slow down. It can be reproduced by follow HBase shell commands.
> {code:java}
> create 'test', 'c'
> java_import org.apache.hadoop.hbase.client.Delete
> java_import org.apache.hadoop.hbase.TableName
> java_import java.lang.System
> con = @hbase.instance_variable_get(:@connection)
> table = con.getTable(TableName.valueOf('test'))
> 1000.times do |i|
>   # batch 10000 deletes with different timestamps every 10 seconds
>   now = System.currentTimeMillis()
>   dels = 10000.times.map do |i|
>     del = Delete.new(Bytes.toBytes('row'))
>     del.addFamily(Bytes.toBytes('c'), now + i)
>   end
>   table.delete(dels)
>   sleep(10)
>   puts "i - #{i}"
>   get 'test', 'row'
> end
> {code}
> {code:java}
> i - 0
> COLUMN                                                                                      CELL
> 0 row(s)
> Took 0.0251 seconds
> ...
> i - 10
> COLUMN                                                                                      CELL
> 0 row(s)
> Took 0.0412 seconds
> ...
> i - 20
> COLUMN                                                                                      CELL
> 0 row(s)
> Took 0.0760 seconds
> ...
> i - 30
> COLUMN                                                                                      CELL
> 0 row(s)
> Took 0.1014 seconds
> ...
> i - 40
> COLUMN                                                                                      CELL
> 0 row(s)
> Took 0.1616 seconds
> ...
> {code}
> But the performance of Get operations can be optimized by using SEEK_NEXT_COL.
> {code:java}
> i - 1
> COLUMN                                                                                      CELL
> 0 row(s)
> Took 0.0087 seconds
> ...
> i - 11
> COLUMN                                                                                      CELL
> 0 row(s)
> Took 0.0077 seconds
> ...
> i - 21
> COLUMN                                                                                      CELL
> 0 row(s)
> Took 0.0087 seconds
> ...
> {code}
> Please review the PR.
> [https://github.com/apache/hbase/pull/6557]



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