Apache HBase Table Snapshots
Matteo Bertozzi | Cloudera | Software Engineer / HBase Committer
Jonathan Hsieh | Cloudera | Software Engineer / HBase Committer
Jesse Yates | Salesforce.com | Software Engineer / HBase Committer
June 13, 2013
HBaseCon 2013

Outline
• Intro and Use Cases
• Usage Instructions
• Internals
• Snapshot Layout
• Snapshot Restoration
• Online Snapshots
• Conclusion

HBase Table Snapshots
Snapshot is a collection of
metadata required to
reconstitute the data near
a particular point in time
HBaseCon 2013 6/13/20133

HBase Table Snapshots
• An inexpensive way to freeze state of a
table
• A mechanism that helps backup data to
in the cluster or to a remote cluster
• Recover from user error
• Bootstrap Replication
HBaseCon 2013 6/13/20134

Old: HBase-Supported Batch Backups
• Export / Dist CP / Import
• 3 batch MR jobs
• Several extra copies of data
• High latency (hours)
• Impacts existing low-latency
workloads
• Copy Table
• 1 MR Job
• Single copy of data
• Incremental table copies
• High Latency (hours)
• Impacts existing workloads
Export
MR Job
Import
MR Job
Dist CP
MR Job
Copy Table
MR Job
HBaseCon 2013 6/13/20135

Upcoming: HDFS Snapshots (or DistCP backup)
• Take an hdfs snapshot of all the
files in the underlying HBase’s
data directory.
• Hfiles, hlogs, and other
metadata.
• Snapshots all tables in Hbase
• Cannot Clone tables
• “Restore As”
• Targeted for Hadoop 2.1 /
Hadoop 3.0 DistCP
HLog Append
Flush
Compact
Restart
Recover
HBaseCon 2013 6/13/20136

New: HBase Snapshot-based Backups
• Snapshot, then Export
• 1 MR Job
• Single copy of data
• Little impact on low-latency
workloads
• Export is like distcp directly
from hfds
• No incremental snapshot
copy
HBaseCon 2013
Export
Snapshot
6/13/20137

Export
• Like distcp for a snapshot manifest
• Copy data files without going through HBase’s “front door”
Export
HBaseCon 2013 6/13/20138

Recover from User Error
• How do we recover from user error?
Recovery Time
time
User Error:
drop ‘table’
Service is
restored, major data
loss
Service is down!
Panic! Black magic!
HBaseCon 2013 6/13/20139

Recovering from User Mistakes: Table Snapshots
• Snapshot the state of a table at a certain moment in time
• Restore it or Clone it later, creating a new read write table
• Export it to another cluster with minimal impact on HBase
time
User Error:
drop ‘table’
Service restored, Minor
data loss. Carry on.
Periodic
snapshot
Service is down!
Keep calm!
restore
Periodic
snapshot
HBaseCon 2013 6/13/201310

Usage
What an Admin needs to know

Configuration
• Simple hbase-site.xml configuration
<property>
<name>hbase.snapshot.enabled</name>
<value>true</value>
</property>
• Enabled by default in 0.95+
• Requires user to enable in 0.94.6.1+.
HBaseCon 2013 6/13/201312

Usage: Shell Commands
• snapshot ‘table’, ‘snapshot’
• Table can be offline or online
• list_snapshot [<regex>]
• clone_snapshot ‘snapshot’, ‘dsttable’
• restore_snapshot ‘snapshot’
• delete_snapshot ‘snapshot’
HBaseCon 2013 6/13/201313

Usage: Web UI
HBaseCon 2013 6/13/201314

Usage: Web UI
HBaseCon 2013 6/13/201315

Export: Usage
• Copy “MySnapshot” to a remote HDFS
• $ hbase class org.apache.hadoop.hbase.snapshot.ExportSnapshot -snapshot
MySnapshot -copy-to hdfs:///srv2:8082/hbase -mappers 16
• With permission change on the copy
• $ hbase class org.apache.hadoop.hbase.snapshot.ExportSnapshot -snapshot
MySnapshot -copy-to hdfs:///srv2:8082/hbase -chuser MyUser -chgroup MyGroup
-chmod 700 -mappers 16
HBaseCon 2013 6/13/201316

Debugging and Info
• Dump a snapshot manifest
• Writes to standard out
• Usage
• $ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo -snapshot
test-snapshot
• $ hbase org.apache.hadoop.hbase.snapshot.SnapshotInfo -snapshot
test-snapshot -files
HBaseCon 2013 6/13/201317

Metrics
• Histograms of operation completion
• snapshotTime
• cloneTime
• restoreTime
• Includes ‘extended’ metrics
• Std deviation
• Min/max
HBaseCon 2013 6/13/201318

Table Snapshot Internals

Internals
• HBase Table HDFS Layout
• Snapshot HDFS layout
• Offline Snapshots
• Restore and Clone Snapshot
• Online Snapshots
HBaseCon 2013 6/13/201320

Primer: HBase Table Layout in HDFS
• HRegions map directly to a directory structure
with table name, encoded region
name, column family and hfiles.
• In HDFS:
/hbase/Table/<enc R1>/cf/<hfile f11>
/hbase/Table/<enc R1>/cf/<hfile f12>
/hbase/Table/<enc R2>/cf/<hfile f21>
/hbase/Table/<enc R2>/cf/<hfile f22>
/hbase/Table/<enc R3>/cf/<hfile f31>
/hbase/Table/<enc R3>/cf/<hfile f32>
Table
F11 F21 F31
R1 R2 R3
6/13/2013HBaseCon 201321

Table Snapshots in the File System
• A Snapshot manifest contains references to files in the original
table.
./.hbase-snapshots
Table
F11 F21 F31
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
HBaseCon 2013 6/13/201322

Table Snapshots in the File System
• A Snapshot manifest contains references to files in the original
table.
• Each snapshot is stored in the hbase/.hbase-snapshots dir.
./.hbase-snapshots
Table
F11 F21 F31
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
HBaseCon 2013 6/13/201323

Offline Snapshots
• Disable table, then create Snapshot Manifest
• Created in temporary dir to guarantee snapshot creation
atomicity
• Includes
• Snapshot Metadata
• Table Metadata/Schema (.tableinfo)
• References to original HFiles
• Master-only file system operation
HBaseCon 2013 6/13/201324

HFile Life Cycle
• Splits and Compactions remove hfiles
• What happens to references to these files?
./.hbase-snapshots
Table
F11 F21 F31
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
HBaseCon 2013 6/13/201325

HFile Life Cycle
• Splits and Compactions remove hfiles
• What happens to references to these files?
./.hbase-snapshots
Table
F11 F21 F31
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
HBaseCon 2013 6/13/201326

HFile Life Cycle
• Splits and Compactions remove hfiles
• What happens to references to these files?
./.hbase-snapshots
Table
F11 F21
F31
+32
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
No more
Hfile??
HBaseCon 2013 6/13/201327

HFile Archiver
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
Table files
F31
HBaseCon 2013 6/13/201328
• We archive old HFiles from compactions (HBASE-5547)

HFile Archiver
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
F31
+32
Table files
F31
HBaseCon 2013 6/13/201329
• We archive old HFiles from compactions (HBASE-5547)
• Files stored in hbase/.archive

HFile Archiver
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
F31
+32
Table files
F31
• We archive old HFiles from compactions (HBASE-5547)
• Files stored in hbase/.archive
• HFileCleaner ensures HFiles’ data remains available
HBaseCon 2013 6/13/201330

Restore Snapshot Internals

Restore Operations
• Restore table
• Rollback table to specific state
• Clone from snapshot (Restore As)
• Create new read-write table from snapshot
• There can be multiple replicas of a snapshot
• Export snapshot
• Send snapshot and all its data to another cluster
HBaseCon 2013 6/13/201332

Clone: Creating table from a Snapshot
• Convert snapshot manifest info into a Table.
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
Table files
Clone
R1 R2 R3
F31
HBaseCon 2013 6/13/201333

Clone: Creating table from a Snapshot
• Convert snapshot manifest info into a Table.
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
Table files
Clone
R1 R2 R3
F31
HBaseCon 2013 6/13/201334

Clone: Creating table from a Snapshot
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
F31
+32
Table files
F31
Clone
R1 R2 R3
• Convert snapshot manifest info into a Table.
• HFileLinks (HBASE-6610) to mimic unix open file descriptor semantics
HBaseCon 2013 6/13/201335

Restore: Rollback to an old state
• Rollback the existing table to snapshot state
• Restores original schema if altered
• Snapshots current table, just in case
• Minimal overhead
• Smarter delete table & clone snapshot
• Handles creating/deleting regions
• Restore META
HBaseCon 2013 6/13/201336

Restore illustrated
./.hbase-snapshots
./.archive
TableSnapshot manifest
R1 R2 R3
Table files
F31
Table
F11 F21
R1 R2 R3
F31
+32 F41
R4
• Rollback “Table” to the “TableSnapshot” state
HBaseCon 2013 6/13/201337

Restore illustrated
./.hbase-snapshots
./.archive
TableSnapshot manifest
R1 R2 R3
Table files
F31
Table
F11 F21
R1 R2 R3
F31
+32 F41
R4
• Region “R4” is not present in the snapshot
• “R4” will be removed from “Table”, files moved to “.archive”
HBaseCon 2013 6/13/201338

Restore illustrated
./.hbase-snapshots
./.archive
TableSnapshot manifest
R1 R2 R3
Table files
F31
Table
F11 F21
R1 R2 R3
F31
+32
F41
• New files not present in the snapshots are moved to the archive
HBaseCon 2013 6/13/201339

Restore illustrated
./.hbase-snapshots
./.archive
TableSnapshot manifest
R1 R2 R3
Table files
F31
Table
F11 F21
R1 R2 R3
F41F3+
32
• New files not present in the snapshots are moved to the archive
• HFileLinks are created to point to old files.
HBaseCon 2013 6/13/201340

Restore failures
• The table to restore is disabled
• META and HDFS operations may fail (network issue, server down, …)
• hbck can’t repair an incomplete restore...
• Restore again!
HBaseCon 2013 6/13/201341

Export Snapshot
• Copy a full snapshot to another cluster
• All required HFiles, and Metadata
• Lots of options
• Fancy dist-cp
• Must resolve HFileLinks
• Faster than CopyTable or table export+import!
• Minimal impact on running cluster
HBaseCon 2013 6/13/201342

Online Snapshots

Online snapshots
• Take a snapshot without making the table
unavailable
• No need to disable the table
• Continue accepting reads and writes from
clients
• Challenges
• Coordinating Region Servers
• Data is in memory
• Consistency
HBaseCon 2013 6/13/201344

Offline vs Online Snapshots
Offline Online
mastermaster
RS1 RS2 RS3 RS4
verify
Snapshot
region
subprocedure
Write
manifest
per region
verify
Write
manifest
per region
6/13/2013HBaseCon 201345

Online Snapshots
• Each Region can have data in memstore and hlog, not yet Hfile
• Snapshot is missing in memory data!
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
TableSnapshot manifest
R1 R2 R3
Table files
F31
mem mem mem
HBaseCon 2013 6/13/201346

Online Snapshots
• Flush so that all in memory data written in an Hfile
• Then add to snapshot manifest
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
Table files
F31
F13 F23 F33
TableSnapshot manifest
R1 R2 R3
HBaseCon 2013 6/13/201347

Online Snapshots
• Flush so that all in memory data in an Hfile
• Then add to snapshot manifest
./.hbase-snapshots
./.archive
Table
F11 F21
R1 R2 R3
Table files
F31
F13 F23 F33
TableSnapshot manifest
R1 R2 R3
HBaseCon 2013 6/13/201348

Consistency
• Offline Snapshots
• Fully consistent snapshot
• Online Flush Snapshot
• “CopyTable” level consistency with a much smaller window.
• Time bounded by slowest region server and region flush
HBaseCon 2013 6/13/201349

Online Snapshots and Causal consistency
• Causal consistency would only allow A, AB, or neither A nor B.
• B and Not A is currently possible
Table
F11 F21
R1 R2 R3
F31
TableSnapshot manifest
R1 R2 R3
Master RS1 RS2 Client
mem mem
Flush SS
F13
HBaseCon 2013 6/13/201350

Online Snapshots and Causal consistency
• Causal consistency would only allow A, AB, or neither A nor B.
• B and Not A is currently possible
Table
F11 F21
R1 R2 R3
F31
TableSnapshot manifest
R1 R2 R3
Master RS1 RS2 Client
mem mem
Put A …
… then
Put B
F13
mem
HBaseCon 2013 6/13/201351

Online Snapshots and Causal consistency
• Causal consistency would allow A, AB, or neither A nor B.
• B and Not A is possible with Flush Snapshots
Table
F11 F21
R1 R2 R3
F31
TableSnapshot manifest
R1 R2 R3
Master RS1 RS2 Client
mem
F23
F13
Flush SS
Put B is
in but
Put A is
not!
F33
HBaseCon 2013 6/13/201352

Online snapshot attempts can fail
• If involved RS’s fail, the snapshots attempt will fail.
• Needs a way to prevent other table metadata operations
• Table Metadata Locks (0.95+)
• Avoid many snapshot failures conflicts(Ex: Online schema, splits)
• Failed attempt will report errors -- user must retry.
• o.a.h.hbase.snapshot.HBaseSnapshotException
• o.a.h.hbase.snapshot.CorruptedSnapshotException
HBaseCon 2013 6/13/201353

Development Notes
How we collaborated, built, and tested

Table Snapshots Development
• Developed in a Branch off of trunk
merged and in 0.95 and trunk.
• Feature is too big to include as a single
patch
• Does not destabilize trunk
• Does not slow time-based release
trains
• Later Backported to 0.94.6.1
src
branch
Reintegrate
into trunk
sync
HBaseCon 2013 6/13/201355

System testing with Jenkins
• Concurrently load data while taking snapshots
• Inject compactions, Kill RS’s, Meta RS, Master
• Create snapshot clones of the snapshots
• Inject Compactions, Kill RS’s, META Rs, Master
HBaseCon 2013 6/13/201356

Future Work:
• Alternative semantics and implementations
• Log Roll Snapshot (HBASE-7291)
• Store logs and replay on restore
• Faster for snapshot, slower and more complicated for restore.
• Timestamp Snapshot (HBASE-6866)
• All updates before ts in snapshot, all after not in snapshot
• Longer pause before snapshot taken
• Globally-Consistent Snapshot (HBASE-6867)
• global write lock for all regions nodes until snapshot complete.
• Expensive
• Repair tools
• Manual repairs necessary (hbck does not support yet)
HBaseCon 2013 6/13/201357

Conclusions

Feature Summary by Version
Apache 0.92.x
Apache <0.94.6.1
Apache 0.94.6.1+ Apache 0.95.0
Apache 0.96.0
Copy Table Copy Table Copy Table
Import / Export Import / Export Import / Export
Offline snapshots Offline snapshots
Flush Online
Snapshot
Flush Online
Snapshot
Table Locks
HBaseCon 2013 6/13/201359

Key Contributors
• Jesse Yates (Salesforce.com)
• HFileArchiver, Offline Snapshot, first draft online
• Matteo Bertozzi (Cloudera)
• HFileLink, Restore, clone, Testing, 0.94 backport
• Jonathan Hsieh (Cloudera)
• Online Snapshots revamp, Testing, Branch Sheppard
• Ted Yu (HortonWorks)
• Reviews
• Enis Soztutar (HortonWorks)
• Table Locks on Snapshots
HBaseCon 2013 6/13/201360

Thanks! Questions?
Matteo Bertozzi
@th30z
matteo.bertozzi@cloudera.com
Jonathan Hsieh
@jmhsieh
jon@cloudera.com
Jesse Yates
@jesse_yates
jesse.k.yates@gmail.com
HBaseCon 2013 6/13/201361