[HBASE-4435] Add Group By functionality using Coprocessors

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Abandoned
• Component/s: Coprocessors
• Labels: by coprocessors group hbase
• Assignee: Unassigned
• Reporter: Nichole Treadway
• Created: 19/Sep/11 14:03
• Updated: 12/Jun/22 19:31
• Resolved: 11/Jun/22 18:46

Description

Adds in a Group By -like functionality to HBase, using the Coprocessor framework.

It provides the ability to group the result set on one or more columns (groupBy families). It computes statistics (max, min, sum, count, sum of squares, number missing) for a second column, called the stats column.

To use, I've provided two implementations.

1. In the first, you specify a single group-by column and a stats field:

statsMap = gbc.getStats(tableName, scan, groupByFamily, groupByQualifier, statsFamily, statsQualifier, statsFieldColumnInterpreter);

The result is a map with the Group By column value (as a String) to a GroupByStatsValues object. The GroupByStatsValues object has max,min,sum etc. of the stats column for that group.

2. The second implementation allows you to specify a list of group-by columns and a stats field. The List of group-by columns is expected to contain lists of

{column family, qualifier}

pairs.

statsMap = gbc.getStats(tableName, scan, listOfGroupByColumns, statsFamily, statsQualifier, statsFieldColumnInterpreter);

The GroupByStatsValues code is adapted from the Solr Stats component.

Issue Links

• relates to: HBASE-1512 Coprocessors: Support aggregate functions
• relates to: HBASE-7474 Endpoint Implementation to support Scans with Sorting of Rows based on column values(similar to "order by" clause of RDBMS)