HBASE-1812 Document fact that Scanners do not respect row locks
git-svn-id: https://svn.apache.org/repos/asf/hadoop/hbase/trunk@811568 13f79535-47bb-0310-9956-ffa450edef68
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@ -56,7 +56,10 @@ import org.apache.hadoop.hbase.util.Writables;
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/**
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* Used to communicate with a single HBase table.
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* <p>
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* This class is not MT safe for writes.
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* This class is not thread safe for writes.
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* Gets, puts, and deletes take out a row lock for the duration
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* of their operation. Scans (currently) do not respect
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* row locking.
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*/
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public class HTable implements HTableInterface {
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private final HConnection connection;
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@ -30,14 +30,13 @@ Provides HBase Client
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<p>To administer HBase, create and drop tables, list and alter tables,
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use {@link org.apache.hadoop.hbase.client.HBaseAdmin}. Once created, table access is via an instance
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of {@link org.apache.hadoop.hbase.client.HTable}. You add content to a table a row at a time. To insert,
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create an instance of a {@link org.apache.hadoop.hbase.client.Put} object and after setting it appropriately,
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commit your update using {@link org.apache.hadoop.hbase.client.HTable#put(Put)}.
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To fetch your inserted
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value, use {@link org.apache.hadoop.hbase.client.Get}. The Get can be specified to be broad -- get all
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on a particular row -- or narrow; return only a single cell value.
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When finished with your Get settings, invoke {@link org.apache.hadoop.hbase.client.HTable#get(Get)}. Use
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{@link org.apache.hadoop.hbase.client.Scan} to set up a scanner -- a Cursor-like access. After
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configuring your Scan instance, call {@link org.apache.hadoop.hbase.client.HTable#getScanner(Scan)} and then
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create an instance of a {@link org.apache.hadoop.hbase.client.Put} object. Specify value, target column
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and optionally a timestamp. Commit your update using {@link org.apache.hadoop.hbase.client.HTable#put(Put)}.
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To fetch your inserted value, use {@link org.apache.hadoop.hbase.client.Get}. The Get can be specified to be broad -- get all
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on a particular row -- or narrow; i.e. return only a single cell value. After creating an instance of
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Get, invoke {@link org.apache.hadoop.hbase.client.HTable#get(Get)}. Use
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{@link org.apache.hadoop.hbase.client.Scan} to set up a scanner -- a Cursor- like access. After
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creating and configuring your Scan instance, call {@link org.apache.hadoop.hbase.client.HTable#getScanner(Scan)} and then
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invoke next on the returned object. Both {@link org.apache.hadoop.hbase.client.HTable#get(Get)} and
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{@link org.apache.hadoop.hbase.client.HTable#getScanner(Scan)} return a
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{@link org.apache.hadoop.hbase.client.Result}.
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@ -47,6 +46,9 @@ in different formats.
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You can remove individual cells or entire families, etc. Pass it to
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{@link org.apache.hadoop.hbase.client.HTable#delete(Delete)} to execute.
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</p>
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<p>Puts, Gets and Deletes take out a lock on the target row for the duration of their operation.
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Scans (currently) operate without respect for row locks.
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</p>
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<p>Client code accessing a cluster finds the cluster by querying ZooKeeper.
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This means that the ZooKeeper quorum to use must be on the client CLASSPATH.
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Usually this means make sure the client can find your <code>hbase-site.xml</code>.
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