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From "Matteo Bertozzi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-15469) Take snapshot by family
Date Fri, 18 Mar 2016 20:14:33 GMT

    [ https://issues.apache.org/jira/browse/HBASE-15469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15202069#comment-15202069

Matteo Bertozzi commented on HBASE-15469:

I have no strong opinion. I'd like to hear someone else opinion talking from a user point
of view. 

cloning a snapshot and having just a subset of the columns will probably be weird.  maybe
is better to just create a table with  only the subset of columns that are going to be populated.

restore snapshot is a bit more complex. because in theory you expect only the families that
you snapshotted are restored and the other families are kept. but that may result in data
missing if new rows are added to the table you snapshotted. 

so, I have no idea. what is the best option. I guess it depends on the use case. 
If you don't use restore/clone of a snapshot with a subset of families as a backup, but just
use it for MR purpose then you don't have these problems. 
we may block the restore of snapshots with only a subset of families. and that will solve
the strange situation of restore. 
and when we clone we just create a new table with only the subset. In theory this is more
clear for the end user. 
but again, I'd like to hear other opinions and use cases

> Take snapshot by family
> -----------------------
>                 Key: HBASE-15469
>                 URL: https://issues.apache.org/jira/browse/HBASE-15469
>             Project: HBase
>          Issue Type: Improvement
>          Components: snapshots
>    Affects Versions: 2.0.0
>            Reporter: Jianwei Cui
>         Attachments: HBASE-15469-v1.patch, HBASE-15469-v2.patch
> In our production environment, there are some 'wide' tables in offline cluster. The 'wide'
table has a number of families, different applications will access different families of the
table through MapReduce. When some application starting to provide online service, we need
to copy needed families from offline cluster to online cluster. For future write, the inter-cluster
replication supports setting families for table, we can use it to copy future edits for needed
families. For existed data, we can take snapshot of the table on offline cluster, then exploit
{{ExportSnapshot}} to copy snapshot to online cluster and clone the snapshot. However, we
can only take snapshot for the whole table in which many families are not needed for the application,
this will lead unnecessary data copy. I think it is useful to support taking snapshot by family,
so that we can only copy needed data.
> Possible solution to support such function:
> 1. Add family names field to the protobuf definition of {{SnapshotDescription}}
> 2. Allow to set families when taking snapshot in hbase shell, such as:
> {code}
>    snapshot 'tableName', 'snapshotName', 'FamilyA', 'FamilyB', {SKIP_FLUSH => true}
> {code}
> 3. Add family names to {{SnapshotDescription}} in client side
> 4. Read family names from {{SnapshotDescription}} in Master/Regionserver, keep only requested
families when taking snapshot for region.
> Discussions and suggestions are welcomed.

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