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From "Josh Elser (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17852) Add Fault tolerance to HBASE-14417 (Support bulk loaded files in incremental backup)
Date Fri, 01 Dec 2017 17:22:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16274659#comment-16274659
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Josh Elser commented on HBASE-17852:
------------------------------------

bq. Hmm... I don't think we can publish backup/restore without HBASE-16391 in a 2.0 release.
I'd like to have confidence that the feature is rock solid before telling users that it's
ok to use, parallel operations seems like a major shortcoming to me.

Let's dig in on this some more, [~mdrob]. B&R is much more of an "administrative function"
as opposed to a "client feature". My general expectation would be that, most aggressively,
HBase admins (a couple of people) would run incremental backups on the order of "hours", e.g.
incremental backup every 8 hours . I could see the extremely paranoid wanting to do incremental
backups every hour over some collection of tables which _could_ cause issues if we can only
execute one backup operation at a time (I'm thinking along the lines of 3 backup sets, incremental
backups every hour, merging of those backups every few hours, full backup every day, etc).

As such, my opinion differs in that I don't see the lack of concurrent backup operations being
a major impediment for "most" users. I completely agree with you that there will be some users
in which this limitation would be problematic on what they want to use it, but, even for these
edge cases, B&R without this would still have value to them. I think getting this feature
into the hands of users (with the extremely clear caveats on current implementation) would
actually better serve the feature than letting it fester more on JIRA. Thoughts?

> Add Fault tolerance to HBASE-14417 (Support bulk loaded files in incremental backup)
> ------------------------------------------------------------------------------------
>
>                 Key: HBASE-17852
>                 URL: https://issues.apache.org/jira/browse/HBASE-17852
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Vladimir Rodionov
>            Assignee: Vladimir Rodionov
>             Fix For: 2.0.0
>
>         Attachments: HBASE-17852-v1.patch, HBASE-17852-v2.patch, HBASE-17852-v3.patch,
HBASE-17852-v4.patch, HBASE-17852-v5.patch, HBASE-17852-v6.patch, HBASE-17852-v7.patch, HBASE-17852-v8.patch,
HBASE-17852-v9.patch
>
>
> Design approach rollback-via-snapshot implemented in this ticket:
> # Before backup create/delete/merge starts we take a snapshot of the backup meta-table
(backup system table). This procedure is lightweight because meta table is small, usually
should fit a single region.
> # When operation fails on a server side, we handle this failure by cleaning up partial
data in backup destination, followed by restoring backup meta-table from a snapshot. 
> # When operation fails on a client side (abnormal termination, for example), next time
user will try create/merge/delete he(she) will see error message, that system is in inconsistent
state and repair is required, he(she) will need to run backup repair tool.
> # To avoid multiple writers to the backup system table (backup client and BackupObserver's)
we introduce small table ONLY to keep listing of bulk loaded files. All backup observers will
work only with this new tables. The reason: in case of a failure during backup create/delete/merge/restore,
when system performs automatic rollback, some data written by backup observers during failed
operation may be lost. This is what we try to avoid.
> # Second table keeps only bulk load related references. We do not care about consistency
of this table, because bulk load is idempotent operation and can be repeated after failure.
Partially written data in second table does not affect on BackupHFileCleaner plugin, because
this data (list of bulk loaded files) correspond to a files which have not been loaded yet
successfully and, hence - are not visible to the system 



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