org.apache.hadoop.hbase.regionserver
Interface ColumnTracker

All Known Implementing Classes:

ExplicitColumnTracker, ScanWildcardColumnTracker, WildcardColumnTracker

public interface ColumnTracker

Implementing classes of this interface will be used for the tracking and enforcement of columns and numbers of versions during the course of a Get or Scan operation.

Currently there are two different types of Store/Family-level queries.

• ExplicitColumnTracker is used when the query specifies one or more column qualifiers to return in the family.
• WildcardColumnTracker is used when the query asks for all qualifiers within the family.

  This class is utilized by QueryMatcher through two methods:

  • checkColumn(byte[], int, int) is called when a Put satisfies all other conditions of the query. This method returns a QueryMatcher.MatchCode to define what action should be taken.
  • update() is called at the end of every StoreFile or memstore.

    This class is NOT thread-safe as queries are never multi-threaded

    Method Summary

    org.apache.hadoop.hbase.regionserver.QueryMatcher.MatchCode	checkColumn(byte[] bytes, int offset, int length) Keeps track of the number of versions for the columns asked for
    boolean	done()
    ColumnCount	getColumnHint() Used by matcher and scan/get to get a hint of the next column to seek to after checkColumn() returns SKIP.
    void	reset() Resets the Matcher
    void	update() Updates internal variables in between files

    Method Detail

    checkColumn

    org.apache.hadoop.hbase.regionserver.QueryMatcher.MatchCode checkColumn(byte[] bytes,
                                                                            int offset,
                                                                            int length)

    Keeps track of the number of versions for the columns asked for

    Parameters:

    bytes -

    offset -

    length -

    Returns:

    The match code instance.

    update

    void update()

    Updates internal variables in between files

    reset

    void reset()

    Resets the Matcher

    done

    boolean done()

    Returns:

    true when done.

    getColumnHint

    ColumnCount getColumnHint()

    Used by matcher and scan/get to get a hint of the next column to seek to after checkColumn() returns SKIP. Returns the next interesting column we want, or NULL there is none (wildcard scanner). Implementations aren't required to return anything useful unless the most recent call was to checkColumn() and the return code was SKIP. This is pretty implementation detail-y, but optimizations are like that.

    Returns:

    null, or a ColumnCount that we should seek to