5.8. Data Model Operations

The four primary data model operations are Get, Put, Scan, and Delete. Operations are applied via HTable instances.

5.8.1. Get

Get returns attributes for a specified row. Gets are executed via HTable.get.

5.8.2. Put

Put either adds new rows to a table (if the key is new) or can update existing rows (if the key already exists). Puts are executed via HTable.put (writeBuffer) or HTable.batch (non-writeBuffer).

5.8.3. Scans

Scan allow iteration over multiple rows for specified attributes.

The following is an example of a on an HTable table instance. Assume that a table is populated with rows with keys "row1", "row2", "row3", and then another set of rows with the keys "abc1", "abc2", and "abc3". The following example shows how startRow and stopRow can be applied to a Scan instance to return the rows beginning with "row".

public static final byte[] CF = "cf".getBytes();
public static final byte[] ATTR = "attr".getBytes();

HTable htable = ...      // instantiate HTable

Scan scan = new Scan();
scan.addColumn(CF, ATTR);
scan.setStartRow(Bytes.toBytes("row")); // start key is inclusive
scan.setStopRow(Bytes.toBytes("rox"));  // stop key is exclusive
ResultScanner rs = htable.getScanner(scan);
try {
  for (Result r = rs.next(); r != null; r = rs.next()) {
  // process result...
} finally {
  rs.close();  // always close the ResultScanner!

Note that generally the easiest way to specify a specific stop point for a scan is by using the InclusiveStopFilter class.

5.8.4. Delete

Delete removes a row from a table. Deletes are executed via HTable.delete.

HBase does not modify data in place, and so deletes are handled by creating new markers called tombstones. These tombstones, along with the dead values, are cleaned up on major compactions.

See Section, “Delete” for more information on deleting versions of columns, and see Section, “Compaction” for more information on compactions.

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