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https://issues.apache.org/jira/browse/HBASE-17852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16274008#comment-16274008
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Vladimir Rodionov commented on HBASE-17852:
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{quote}
When we switch away from restore-via-snapshot and have proper transactions,
does that mean this extra table will go away?
{quote}
Yes, but you need to understand, that proper Tx management is a hard task in
this case. It is even harder than classic Tx management. DB Tx got rollbacked
automatically in case of a collision (updates to the same record), but we have
to merge these updates correctly, because backup sessions always update shared
records. Is it worth doing? Only Admin can run backups and what is the use case
when Admin starts two sessions in parallel if he can run them serially?
> 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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