A talk given on HBase Replication at HBaseCon 2013.

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@ctrezzo
HBaseCon 2013
Apache HBase Replication
Thursday, July 25, 13

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About me
Active contributor to Apache HBase
Software Engineer @ Twitter
Core Storage Team - Hadoop/HBase
Follow me @ctrezzo
Thursday, July 25, 13

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Agenda
Introduction
High-level Architecture
Replication State
Path of a replicated edit
Replication Source
Replication Sink
Replication Source Manager
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HBase replication
Asynchronously copy data between two HBase clusters
Push-based architecture
WAL shipping technique similar to MySQL
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Guarantees of replication
Eventually consistent
Deliver updates at least once
Atomicity of individual updates will be preserved
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Administering Replication
Simply set parameter in hbase-site.xml
hbase.replication => true
Setup replication topologies
add_peer, remove_peer, disable_peer, enable_peer,
list_peers
Create/Alter tables with replication scope set
REPLICATION_SCOPE => ‘1’
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High-Level Architecture
ReplicationSource
Manager
ReplicationSource
Region Server
Region Server
ReplicationSink HTable
Region Server
Cluster 2Cluster 1
1
2
4
3
HLog
ReplicationSource
Region Server
ReplicationSink HTable
Region Server
Cluster 3
1
/state
/peers
/1
/2
/rs
Zookeeper
123
Replication
Admin
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Replication State
Persistently stored in Zookeeper
Status
Master kill switch
Peers
List of remote target clusters
Queues
List of remaining HLogs to replicate and current position in
each log
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Path of a replicated edit
ReplicationSource
Region Server
Region Server
ReplicationSink HTable
Region Server
Cluster 2Cluster 1
1
2
4
3
HLog
123
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Path of a replicated edit
ReplicationSource
Region Server 1
Region Server
ReplicationSink HTable
Region Server
Cluster 2Cluster 1
1
2
4
3
HLog
123
ReplicationSource
Region Server 2
Region Server
ReplicationSink HTable
Region Server
1
2
4
3
HLog
12
ReplicationSource
Region Server X
Region Server
ReplicationSink HTable
Region Server
1
2
4
3
HLog
1
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End-point for shipping WAL entries
One instance for each queue
Runs as a separate thread on region server
Uses AdminProtocol RPC to synchronously ship entries
Filters edits based on replication scope
ReplicationSource
Region Server
Region Server
ReplicationSink HTable
Region Server
Cluster 2Cluster 1
1
2
4
3
HLog
123
11
Replication Source
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Replication Sink
End-point for receiving shipped WAL entries
One instance per region server
Synchronously receives entries and applies them using
HTable
Batches rows in the same table
ReplicationSource
Region Server
Region Server
ReplicationSink HTable
Region Server
Cluster 2Cluster 1
1
2
4
3
HLog
123
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Load balancing
Balances load on remote cluster using randomization
Ships edits to random subset of remote region servers
Default is 10%
Cluster 2
20 Region Servers
Cluster 1
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Path of a replicated edit
ReplicationSource
Region Server
Region Server
ReplicationSink HTable
Region Server
Cluster 2Cluster 1
1
2
4
3
HLog
123
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Replication Source Manager
Manages all replication sources
Manages change in replication state
Log rolling
Region server failure
Addition/deletion of peer clusters
ReplicationSource
Manager
ReplicationSource
Region Server
Region Server
ReplicationSink HTable
Region Server
Cluster 2Cluster 1
1
2
4
3
HLog
ReplicationSource
Region Server
ReplicationSink HTable
Region Server
Cluster 3
1
/state
/peers
/1
/2
/rs
Zookeeper
123
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High-Level Architecture
ReplicationSource
Manager
ReplicationSource
Region Server
Region Server
ReplicationSink HTable
Region Server
Cluster 2Cluster 1
1
2
4
3
HLog
ReplicationSource
Region Server
ReplicationSink HTable
Region Server
Cluster 3
1
/state
/peers
/1
/2
/rs
Zookeeper
123
Replication
Admin
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Additional Resources
Apache HBase user mailing list
user@hbase.apache.org
Apache HBase reference guide
https://hbase.apache.org/book.html
Tweet me
@ctrezzo
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Questions?
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Replication State
Persistently stored in Zookeeper
Three major replication znodes: Status, Peers, Queues
/hbase/replication
/state [VALUE: true]
/peers
/1 [Value: zk1.host.com,zk2.host.com,zk3.host.com:2181:/hbase]
/peer-state [Value: ENABLED]
/2 [Value: zk5.host.com,zk6.host.com,zk7.host.com:2181:/hbase]
/peer-state [Value: DISABLED]
/rs
/hostname.example.org,6020,1234
/1
/23522342.23422 [VALUE: 254]
/12340993.22342 [VALUE: 0]
/2
/23522342.23422 [VALUE: 34]
/12340993.22342 [VALUE: 0]
/hostname2.example.org,6020,1234
/1
/23522348.23443 [VALUE: 87]
/12340999.22362 [VALUE: 0]
/2
/23522348.23443 [VALUE: 127]
/12340999.22362 [VALUE: 0]
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Status znode
Master kill switch
Controlled by start_replication, stop_replication
Be careful what you wish for
/hbase/replication
/state [VALUE: true]
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Peers znode
A set of remote clusters registered as possible replication
targets
Identified by peer id
Contains status of each peer cluster
/hbase/replication
/peers
/1 [Value: zk1.host.com,zk2.host.com,zk3.host.com:2181:/hbase]
/peer-state [Value: ENABLED]
/2 [Value: zk5.host.com,zk6.host.com,zk7.host.com:2181:/hbase]
/peer-state [Value: DISABLED]
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Queues znode
Queues identified by region server and peer id
Queues contain list of HLogs and current position in log
/hbase/replication
/rs
/hostname.example.org,6020,1234
/1
/23522342.23422 [VALUE: 254]
/12340993.22342 [VALUE: 0]
/2
/23522342.23422 [VALUE: 34]
/12340993.22342 [VALUE: 0]
/hostname2.example.org,6020,1234
/1
/23522348.23443 [VALUE: 87]
/12340999.22362 [VALUE: 0]
/2
/23522348.23443 [VALUE: 127]
/12340999.22362 [VALUE: 0]
Thursday, July 25, 13