Managing HBase Snapshots

HBase snapshots can be managed using Cloudera Manager or using the command line, as described in these sections:

Using Cloudera Manager

For HBase (CDH 4.2 or later or CDH 5) services, a Table Browser tab is available where you can view the HBase tables associated with a service on your cluster. From here you can view the currently saved snapshots for your tables, and delete or restore them as appropriate. From the HBase Table Browser tab you can:

View the HBase tables that you can snapshot.
Initiate immediate (unscheduled) snapshots of a table.
View the list of saved snapshots currently being maintained. These may include one-off immediate snapshots, as well as scheduled policy-based snapshots.
Delete a saved snapshot.
Restore from a saved snapshot.
Restore a table from a saved snapshot to a new table (Restore As).

Browsing HBase Tables

To browse the HBase tables to view snapshot activity:

From the Clusters tab, select your HBase service.
Go to the Table Browser tab.

Managing HBase Snapshots

Minimum Required Role: BDR Administrator (also provided by Full Administrator)

To take a snapshot,

Click a table.
Click Take Snapshot.
Specify the name of the snapshot, and click Take Snapshot.

To delete a snapshot, click and select Delete.

To restore a snapshot, click and select Restore.

To restore a snapshot to a new table, select Restore As from the menu associated with the snapshot, and provide a name for the new table.

Storing HBase Snapshots on Amazon S3

With Cloudera Manager 5.2 or later and CDH 5.2 or later, HBase snapshots can be stored on the cloud storage service Amazon S3 instead of in HDFS. To configure HBase to store snapshots on Amazon S3, you must have the following information:

The access key ID for your Amazon S3 account.
The secret access key for your Amazon S3 account.
The path to the directory in Amazon S3 where you want your HBase snapshots to be stored.

Configuring HBase in Cloudera Manager to Store Snapshots in Amazon S3

Minimum Required Role: Cluster Administrator (also provided by Full Administrator)

With the above Amazon S3 information at hand, perform the following steps in Cloudera Manager:

Open the HBase service page.
Click Configuration, expand Service-Wide, and click Backup.
Enter your Amazon S3 access key ID in the field AWS S3 access key ID for remote snapshots.
Enter your Amazon S3 secret access key in the field AWS S3 secret access key for remote snapshots.
Enter the path to the location in Amazon S3 where your HBase snapshots should be stored in the field AWS S3 path for remote snapshots.
Warning: Do not use the Amazon S3 location defined by the path entered in AWS S3 path for remote snapshots for any other purpose, or directly add or delete content there. Doing so will risk corrupting the metadata associated with the HBase snapshots stored there. Use this path and Amazon S3 location only through Cloudera Manager, and only for managing HBase snapshots.
In a terminal window, log in to your Cloudera Manager cluster at the command line and create a /user/hbase directory in HDFS. Change the owner of the directory to hbase.
```
Example:
hdfs dfs -mkdir /user/hbase
hdfs dfs -chown hbase /user/hbase
```

Configuring the Dynamic Resource Pool Used for Exporting and Importing Snapshots in Amazon S3

Dynamic resource pools are used to control the resources available for MapReduce jobs created for HBase snapshots on Amazon S3. By default, MapReduce jobs run against the default dynamic resource pool. To choose a different dynamic resource pool for HBase snapshots stored on Amazon S3, follow these steps:

Open the HBase service page.
Click Configuration, expand Service-Wide, and click Backup.
Enter name of a dynamic resource pool in the field Scheduler pool for remote snapshots in AWS S3.
Click Save Changes.

HBase Snapshots on Amazon S3 with Kerberos Enabled

By default, when Kerberos is enabled YARN will not allow MapReduce jobs to be run by the system user hbase. If Kerberos is enabled on your cluster, you must perform the following steps:

Open the YARN service page in Cloudera Manager.
Click Configuration, expand NodeManager Default Group, and click Security.
In Allowed System Users, click the + sign and add hbase to the list of allowed system users.
Click Save Changes.
Restart the YARN service.

Managing HBase Snapshots on Amazon S3 in Cloudera Manager

Minimum Required Role: BDR Administrator (also provided by Full Administrator)

To take HBase snapshots and store them on Amazon S3, perform the following steps:

On the HBase service page in Cloudera Manager, click the Table Browser tab.
Select a table in the Table Browser. If any recent local or remote snapshots already exist, they will be displayed on the right side.
In the dropdown for the selected table, click Take Snapshot.
Enter a name in the Snapshot Name field of the Take Snapshot dialog.
If Amazon S3 storage is configured as described above, the Take Snapshot dialog box's Destination section will show a choice of Local or Remote S3. Select Remote S3.
Click Take Snapshot.
While the Take Snapshot command is being executed, a local copy of the snapshot with a name beginning cm-tmp followed by an auto-generated filename is displayed in the Table Browser, but this local copy is deleted as soon as the remote snapshot has been stored in Amazon S3. If the command fails without being completed, the temporary local snapshot may be left behind. This copy can be manually deleted or kept as a valid local snapshot. To store a current snapshot in Amazon S3, either execute the Take Snapshot command again, selecting Remote S3 as the Destination, or use the HBase command-line tools to manually export the existing temporary local snapshot to Amazon S3.

Deleting HBase Snapshots from Amazon S3

To delete a snapshot stored in Amazon S3:

Select the snapshot in the Table Browser.
Click the dropdown arrow for the snapshot.
Click Delete.

Restoring an HBase Snapshot from Amazon S3

To restore an HBase snapshot that is stored in Amazon S3:

Select the table in the Table Browser.
Click Restore Table.
Choose Remote S3 and select the table to restore.
Click Restore.
Cloudera Manager will create a local copy of the remote snapshot with a name beginning with cm-tmp followed by an auto-generated filename, and will use that local copy to restore the table in HBase. Cloudera Manager will then automatically delete the local copy. If the Restore command fails without being completed, the temporary copy may be left behind and will be seen in the Table Browser. In that case, delete the local temporary copy manually and re-execute the Restore command to restore the table from Amazon S3.

Restoring an HBase Snapshot from Amazon S3 with a New Name

Restoring an HBase snapshot that is stored in Amazon S3 with a new name is a way of cloning the table without affecting the existing table in HBase. To do this, perform the following steps:

Select the table in the Table Browser.
Click Restore Table From Snapshot As.
In the Restore As dialog, enter a new name for the table in the Restore As field.
Select Remote S3 and choose the desired snapshot in the list of available Amazon S3 snapshots.

Managing Policies for HBase Snapshots in Amazon S3

You can configure policies to automatically create snapshots of HBase tables on an hourly, daily, weekly, monthly or yearly basis. Snapshot policies for HBase snapshots stored in Amazon S3 are configured using the same procedures as for local HBase snapshots. These procedures are described in Cloudera Manager Snapshot Policies. The only additional step to perform for snapshots stored in Amazon S3 is to choose Remote S3 in the Destination section of the policy management dialog boxes.

While a snapshot is being made based on a snapshot policy, as with snapshots created manually, a local copy of the snapshot is created, in this case with a name beginning cm-auto followed by an auto-generated filename. The temporary copy of the snapshot is displayed in the Table Browser, but this local copy is deleted as soon as the remote snapshot has been stored in Amazon S3. If the snapshot procedure fails without being completed, the temporary local snapshot may be left behind. This copy can be manually deleted or kept as a valid local snapshot. To export the HBase snapshot to Amazon S3, use the HBase command-line tools to manually export the existing temporary local snapshot to Amazon S3.

Using the Command Line

About HBase Snapshots

In previous HBase releases, the only way to a backup or to clone a table was to use CopyTable or ExportTable, or to copy all the hfiles in HDFS after disabling the table. The disadvantages of these methods are:

CopyTable and ExportTable can degrade region server performance.
Disabling the table means no reads or writes; this is usually unacceptable.

HBase Snapshots allow you to clone a table without making data copies, and with minimal impact on Region Servers. Exporting the table to another cluster should not have any impact on the region servers.

Use Cases

Recovery from user or application errors
- Useful because it may be some time before the database administrator notices the error
  Note:
  The database administrator needs to schedule the intervals at which to take and delete snapshots. Use a script or your preferred management tool for this; it is not built into HBase.
- The database administrator may want to save a snapshot right before a major application upgrade or change.
  Note:
  Snapshots are not primarily used for system upgrade protection because they would not roll back binaries, and would not necessarily be proof against bugs or errors in the system or the upgrade.
- Sub-cases for recovery:
  - Rollback to previous snapshot and merge in reverted data
  - View previous snapshots and selectively merge them into production
Backup
- Capture a copy of the database and store it outside HBase for disaster recovery
- Capture previous versions of data for compliance, regulation, archiving
- Export from snapshot on live system provides a more consistent view of HBase than CopyTable and ExportTable
Audit and/or report view of data at a specific time
- Capture monthly data for compliance
- Use for end-of-day/month/quarter reports
Use for Application testing
- Test schema or application changes on like production data from snapshot and then throw away
- For example: take a snapshot; create a new table from the snapshot content (schema plus data); manipulate the new table by changing the schema, adding and removing rows, and so on (the original table, the snapshot, and the new table remain independent of each other)
Offload work
- Capture, copy, and restore data to another site
- Export data to another cluster

Where Snapshots Are Stored

The snapshot metadata is stored in the .hbase_snapshot directory under the hbase root directory (/hbase/.hbase-snapshot). Each snapshot has its own directory that includes all the references to the hfiles, logs, and metadata needed to restore the table.

hfiles needed by the snapshot are in the traditional /hbase/data/<namespace>/<tableName>/<regionName>/<familyName>/ location if the table is still using them; otherwise they will be placed in /hbase/.archive/<namespace>/<tableName>/<regionName>/<familyName>/

Zero-copy Restore and Clone Table

From a snapshot you can create a new table (clone operation) or restore the original table. These two operations do not involve data copies; instead a link is created to point to the original hfiles.

Changes to a cloned or restored table do not affect the snapshot or (in case of a clone) the original table.

If you want to clone a table to another cluster, you need to export the snapshot to the other cluster and then execute the clone operation; see Exporting a Snapshot to Another Cluster.

Reverting to a Previous HBase Version

Snapshots don’t affect HBase backward compatibility if they are not used.

If you do use the snapshot capability, backward compatibility is affected as follows:

If you only take snapshots, you can still go back to a previous HBase version
If you have used restore or clone, you cannot go back to a previous version unless the cloned or restored tables have no links (there is no automated way to check; you would need to inspect the file system manually).

Storage Considerations

Since the hfiles are immutable, a snapshot consists of reference to the files that are in the table at the moment the snapshot is taken. No copies of the data are made during the snapshot operation, but copies may be made when a compaction or deletion is triggered. In this case, if a snapshot has a reference to the files to be removed, the files are moved to an archive folder, instead of being deleted. This allows the snapshot to be restored in full.

Because no copies are performed, multiple snapshots share the same hfiles, but in the worst case scenario, each snapshot could have different set of hfiles (tables with lots of updates, and compactions).

Configuring and Enabling Snapshots

Snapshots are on by default; to disable them, set the hbase.snapshot.enabled property in hbase-site.xml to false:

<property>
   <name>hbase.snapshot.enabled</name>
   <value>
      false
   </value>
</property>

To enable snapshots after you have disabled them, set hbase.snapshot.enabled to true.

Snapshots don’t affect HBase performance if they are not used.

Shell Commands

You can manage snapshots by using the HBase shell or the HBaseAdmin Java API.

The following table shows actions you can take from the shell:

Action	Shell command	Comments
Take a snapshot of `tableX` called `snapshotX`	snapshot 'tableX', 'snapshotX'	Snapshots can be taken while a table is disabled, or while a table is online and serving traffic. If a table is disabled (using `disable <table>`), an offline snapshot is taken. This snapshot is managed by the master and fully consistent with the state when the table was disabled. This is the simplest and safest method, but it involves a service interruption because the table must be disabled to take the snapshot. In an online snapshot, the table remains available while the snapshot is taken, and incurs minimal performance degradation of normal read/write loads. This snapshot is managed by the master and run on the RegionServers. The current implementation—simple-flush snapshots—provides no causal consistency guarantees. Despite this shortcoming, it offers the same degree of consistency as `CopyTable` and is a significant improvement.
Restore snapshot `snapshotX` (it will replace the source table content)	restore_snapshot ‘snapshotX’	Restoring a snapshot attempts to replace the current version of a table with another version of the table. To run this command, you must disable the target table. The `restore` command takes a snapshot of the table (appending a timestamp code), and then essentially clones data into the original data and removes data not in the snapshot. If the operation succeeds, the target table will be enabled. Use this capability only in an emergency; see Restrictions.
List all available snapshots	list_snapshots
List all available snapshots starting with `‘mysnapshot_’` (regular expression)	list_snapshots ‘my_snapshot_.*’
Remove a snapshot called `snapshotX`	delete_snapshot ‘snapshotX’
Create a new table `tableY` from a snapshot `snapshotX`	clone_snapshot ‘snapshotX’, ‘tableY’	Cloning a snapshot creates a new read/write table that can serve the data kept at the time of the snapshot. The original table and the cloned table can be modified independently without interfering – new data written to one table will not show up on the other.

Taking a Snapshot Using a Shell Script

With HBase in CDH 5.2 and newer, you can take a snapshot using an operating system shell script, such as a Bash script. This is possible because of HBase Shell's new non-interactive mode, which is described in Accessing HBase by using the HBase Shell. This example Bash script illustrates how to take a snapshot in this way. This script is not production-ready, but is provided as an illustration only.

#!/bin/bash
# Take a snapshot of the table passed as an argument
# Usage: snapshot_script.sh table_name
# Names the snapshot in the format snapshot-YYYYMMDD

# Parse the arguments
if [ -z $1 ]||[$1 == '-h' ]; then

echo "Usage: $0 &lt;table&gt;"

echo "       $0 -h"

exit 1
fi

# Modify to suit your environment
export HBASE_PATH=/home/user/hbase
export DATE=`date +"%Y%m%d"`
echo "snapshot '$1', 'snapshot-$DATE'" | $HBASE_PATH/bin/hbase shell -n 
status=$?
if [$status -ne 0]; then

echo "Snapshot may have failed: $status"
fi
exit $status

HBase Shell returns an exit code of 0 on success, but a non-zero exit code only indicates the possibility of failure, rather than definite failure. Therefore, your script should check to see if the snapshot was created before trying again, in the event of a reported failure.

Exporting a Snapshot to Another Cluster

You can export any snapshot from one cluster to another. Exporting the snapshot copies the table's hfiles, logs, and the snapshot's metadata, from the source cluster to the destination cluster. You can specify the -copy-from option to copy from a remote cluster to the local cluster or another remote cluster. If you do not specify the -copy-from option, the hbase.rootdir in the HBase configuration is used, which means that you are exporting from the current cluster.You must specify the -copy-to option, to specify the destination cluster.

The ExportSnapshot tool executes a MapReduce Job, similar to distcp, to copy files to the other cluster. It works at file-system level, so the hbase cluster can be offline. Be sure to run ExportSnapshot as the hbase user or the user that owns the files.

To copy a snapshot called MySnapshot to an HBase cluster srv2 (hdfs://srv2:8020/hbase) using 16 mappers:

hbase class org.apache.hadoop.hbase.snapshot.ExportSnapshot -snapshot MySnapshot -copy-to hdfs://srv2:8020/hbase -mappers 16

To export the snapshot and change the ownership of the files during the copy:

hbase class org.apache.hadoop.hbase.snapshot.ExportSnapshot -snapshot MySnapshot -copy-to hdfs://srv2:8020/hbase -chuser MyUser -chgroup MyGroup -chmod 700 -mappers 16

You can also use the Java -D option in many tools to specify MapReduce or other configuration. properties. For example, the following command copies MY_SNAPSHOT to hdfs://cluster2/hbase using groups of 10 hfiles per mapper:

hbase org.apache.hadoop.hbase.snapshot.ExportSnapshot -Dsnapshot.export.default.map.group=10 -snapshot MY_SNAPSHOT -copy-to hdfs://cluster2/hbase

(The number of mappers is calculated as TotalNumberOfHFiles/10.)

To export from one remote cluster to another remote cluster, specify both -copy-from and -copy-to parameters. You could then reverse the direction to restore the snapshot bacvk to the first remote cluster.

hbase org.apache.hadoop.hbase.snapshot.ExportSnapshot -snapshot snapshot-test -copy-from hdfs://machine1/hbase -copy-to hdfs://machine2/my-backup

To specify a different name for the snapshot on the target cluster, use the -target option.

hbase org.apache.hadoop.hbase.snapshot.ExportSnapshot -snapshot snapshot-test -copy-from hdfs://machine1/hbase -copy-to hdfs://machine2/my-backup -target new-snapshot

Restrictions

All the Masters and Region Servers must be running CDH 5.
If you have enabled the AccessController Coprocessor for HBase, only a global administrator can take, clone, or restore a snapshot, and these actions do not capture the ACL rights. This means that restoring a table preserves the ACL rights of the existing table, while cloning a table creates a new table that has no ACL rights until the administrator adds them.
Do not take, clone, or restore a snapshot during a rolling restart. Snapshots rely on the Region Servers being up; otherwise the snapshot will fail.
Note: This restriction also applies to rolling upgrade, which can currently be done only via Cloudera Manager.

If you are using HBase Replication and you need to restore a snapshot: If you are using HBase Replication the replicas will be out of synch when you restore a snapshot. Do this only in an emergency.

If you need to restore a snapshot, proceed as follows:

Disable the table that is the restore target, and stop the replication
Remove the table from both the master and slave clusters
Restore the snapshot on the master cluster
Create the table on the slave cluster and use CopyTable to initialize it.

Snapshot Failures

Region moves, splits, and other metadata actions that happen while a snapshot is in progress will probably cause the snapshot to fail; the software detects and rejects corrupted snapshot attempts.

Information and Debugging

You can use the SnapshotInfo tool to get information about a snapshot, including status, files, disk usage, and debugging information.

Examples:

Use the -h option to print usage instructions for the SnapshotInfo utility.

$ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo -h
Usage: bin/hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo [options]
 where [options] are:
  -h|-help                Show this help and exit.
  -remote-dir             Root directory that contains the snapshots.
  -list-snapshots         List all the available snapshots and exit.
  -snapshot NAME          Snapshot to examine.
  -files                  Files and logs list.
  -stats                  Files and logs stats.
  -schema                 Describe the snapshotted table.

Use the -list-snapshots option to list all snapshots and exit. This option is new in CDH 5.1.

$ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo -list-snapshots
SNAPSHOT             | CREATION TIME        | TABLE NAME
snapshot-test        |  2014-06-24T19:02:54 | test

Use the -remote-dir option with the -list-snapshots option to list snapshots located on a remote system.

$ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo -remote-dir s3n://mybucket/mysnapshot-dir -list-snapshots
SNAPSHOT |   CREATION TIME  | TABLE NAME
snapshot-test        2014-05-01 10:30    myTable

Use the -snapshot option to print information about a specific snapshot.

$ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo -snapshot test-snapshot
Snapshot Info
----------------------------------------
   Name: test-snapshot
   Type: DISABLED
  Table: test-table
Version: 0
Created: 2012-12-30T11:21:21
**************************************************************

Use the -snapshot with the -stats options to display additional statistics about a snapshot.

$ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo -stats -snapshot snapshot-test
Snapshot Info
----------------------------------------
   Name: snapshot-test
   Type: FLUSH
  Table: test
 Format: 0
Created: 2014-06-24T19:02:54


1 HFiles (0 in archive), total size 1.0k (100.00% 1.0k shared with the source table)

Use the -schema option with the -snapshot option to display the schema of a snapshot.

$ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo  -schema -snapshot snapshot-test
Snapshot Info
----------------------------------------
   Name: snapshot-test
   Type: FLUSH
  Table: test
 Format: 0
Created: 2014-06-24T19:02:54

Table Descriptor
----------------------------------------
'test', {NAME => 'cf', DATA_BLOCK_ENCODING => 'FAST_DIFF', BLOOMFILTER => 'ROW', REPLICATION_SCOPE => '0', 
COMPRESSION => 'GZ', VERSIONS => '1', TTL => 'FOREVER', MIN_VERSIONS => '0', KEEP_DELETED_CELLS => 'false', 
BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}

Use the -files option with the -snapshot option to list information about files contained in a snapshot.

$ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo -snapshot test-snapshot -files
Snapshot Info
----------------------------------------
   Name: test-snapshot
   Type: DISABLED
  Table: test-table
Version: 0
Created: 2012-12-30T11:21:21

Snapshot Files
----------------------------------------
   52.4k test-table/02ba3a0f8964669520cf96bb4e314c60/cf/bdf29c39da2a4f2b81889eb4f7b18107 (archive)
   52.4k test-table/02ba3a0f8964669520cf96bb4e314c60/cf/1e06029d0a2a4a709051b417aec88291 (archive)
   86.8k test-table/02ba3a0f8964669520cf96bb4e314c60/cf/506f601e14dc4c74a058be5843b99577 (archive)
   52.4k test-table/02ba3a0f8964669520cf96bb4e314c60/cf/5c7f6916ab724eacbcea218a713941c4 (archive)
  293.4k test-table/02ba3a0f8964669520cf96bb4e314c60/cf/aec5e33a6564441d9bd423e31fc93abb (archive)
   52.4k test-table/02ba3a0f8964669520cf96bb4e314c60/cf/97782b2fbf0743edaacd8fef06ba51e4 (archive)

6 HFiles (6 in archive), total size 589.7k (0.00% 0.0 shared with the source table)
0 Logs, total size 0.0

Cloudera Manager Snapshot Policies

Managing HDFS Snapshots