Querying Secondary Regions
You can query HA-enabled HBase tables with the Java API or HBase Shell.
This section describes how to query HA-enabled HBase tables.
Querying HBase with the Java API
The HBase Java API allows application developers to specify the desired data consistency for a
query using the setConsistency() method, as shown in the following example. A new enum, CONSISTENCY
,
specifies two levels of data consistency: TIMELINE
and STRONG
.
Get get = new Get(row); get.setConsistency(CONSISTENCY.TIMELINE); ... Result result = table.get(get);
HBase application developers can also pass multiple gets
:
Get get1 = new Get(row); get1.setConsistency(Consistency.TIMELINE); ... ArrayList<Get> gets = new ArrayList<Get>(); ... Result[] results = table.get(gets);
The setConsistency()
method is also available for Scan objects:
Scan scan = new Scan(); scan.setConsistency(CONSISTENCY.TIMELINE); ... ResultScanner scanner = table.getScanner(scan);
In addition, you can use the Result.isStale()
method to determine whether the query
results arrived from the primary or a secondary replica:
Result result = table.get(get); if (result.isStale()) { ... }
Querying HBase Interactively
To specify the desired data consistency for each query, use the HBase shell:
hbase(main):001:0> get 't1', 'r6', {CONSISTENCY => "TIMELINE"}
Interactive scans also accept this syntax:
hbase(main):001:0> scan 't1', {CONSISTENCY => 'TIMELINE'}
Note | |
---|---|
This release of HBase does not provide a mechanism to determine if the results from an interactive query arrived from the primary or a secondary replica. |
You can also request a specific region replica for debugging:
hbase> get 't1', 'r6', {REGION_REPLICA_ID=>0, CONSISTENCY=>'TIMELINE'} hbase> get 't1', 'r6', {REGION_REPLICA_ID=>2, CONSISTENCY=>'TIMELINE'}