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From "Duo Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14949) Resolve name conflict when splitting if there are duplicated WAL entries
Date Wed, 17 Feb 2016 05:38:18 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14949?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15149920#comment-15149920
] 

Duo Zhang commented on HBASE-14949:
-----------------------------------

The problem here is we can not change the meaning of final file name otherwise we can not
do rolling upgrade, so we must merge them into one file or delete one...

And without multi WAL, I do not think there will be overlap? There should not be holes in
WAL file.

For example, if a region has WAL entries with sequence id 1,2,3, for a WAL file that contains
some WAL entries of this region, the possible result is

contains 1
contains 2
contains 3
contains 1,2
contains 2,3
contains 1,2,3

You can see that, conflict could happen with
2 and 1,2
3 and 2,3
3 and 1,2,3
2,3 and 1,2,3
each with itself.

There will not be overlaps.

> Resolve name conflict when splitting if there are duplicated WAL entries
> ------------------------------------------------------------------------
>
>                 Key: HBASE-14949
>                 URL: https://issues.apache.org/jira/browse/HBASE-14949
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Heng Chen
>            Assignee: Duo Zhang
>         Attachments: HBASE-14949-v3.patch, HBASE-14949-v4.patch, HBASE-14949.patch, HBASE-14949_v1.patch,
HBASE-14949_v2.patch
>
>
> The AsyncFSHLog introduced in HBASE-14790 may write same WAL entries to different WAL
files. WAL entry itself is idempotent so replay is not a problem but the intermediate file
name and final name when splitting is constructed using the lowest or highest sequence id
of the WAL entries written, so it is possible that different WAL files will have same intermediate
or final file name when splitting. In the currentm implementation, this will cause split fail
or data loss. We need to solve this.



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