mondrian.rolap.agg

Class Segment

java.lang.Object

mondrian.rolap.agg.Segment

Direct Known Subclasses:

SegmentWithData

public class Segment
extends Object

A Segment is a collection of cell values parameterized by a measure, and a set of (column, value) pairs. An example of a segment is

(Unit sales, Gender = 'F', State in {'CA','OR'}, Marital Status = anything)

All segments over the same set of columns belong to an Aggregation, in this case:

('Sales' Star, Gender, State, Marital Status)

Note that different measures (in the same Star) occupy the same Aggregation. Aggregations belong to the AggregationManager, a singleton.

Segments are pinned during the evaluation of a single MDX query. The query evaluates the expressions twice. The first pass, it finds which cell values it needs, pins the segments containing the ones which are already present (one pin-count for each cell value used), and builds a cell request for those which are not present. It executes the cell request to bring the required cell values into the cache, again, pinned. Then it evalutes the query a second time, knowing that all cell values are available. Finally, it releases the pins.

A Segment may have a list of Segment.ExcludedRegion objects. These are caused by cache flushing. Usually a segment is a hypercube: it is defined by a set of values on each of its axes. But after a cache flush request, a segment may have a rectangular 'hole', and therefore not be a hypercube anymore.

For example, the segment defined by {CA, OR, WA} * {F, M} is a 2-dimensional hyper-rectangle with 6 cells. After flushing {CA, OR, TX} * {F}, the result is 4 cells:

     F     M
 CA  out   in
 OR  out   in
 WA  in    in
 

defined by the original segment minus the region ({CA, OR} * {F}).

Since:

21 March, 2002

Author:

jhyde

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Segment.ExcludedRegion Definition of a region of values which are not in a segment.

Field Summary

Fields

Modifier and Type	Field and Description
protected RolapStar.Column[]	columns This is set in the load method and is used during the processing of a particular aggregate load.
protected List<StarPredicate>	compoundPredicateList
protected BitKey	constrainedColumnsBitKey
protected List<Segment.ExcludedRegion>	excludedRegions List of regions to ignore when reading this segment.
RolapStar.Measure	measure
StarColumnPredicate[]	predicates An array of axes, one for each constraining column, containing the values returned for that constraining column.
protected RolapStar	star

Constructor Summary

Constructors

Constructor and Description
Segment(RolapStar star, BitKey constrainedColumnsBitKey, RolapStar.Column[] columns, RolapStar.Measure measure, StarColumnPredicate[] predicates, List<Segment.ExcludedRegion> excludedRegions, List<StarPredicate> compoundPredicateList) Creates a Segment; it's not loaded yet.

Method Summary

Modifier and Type	Method and Description
protected void	describeAxes(StringBuilder buf, int i, boolean values)
RolapStar.Column[]	getColumns() Returns the constrained columns.
List<StarPredicate>	getCompoundPredicateList() Returns the list of compound predicates.
BitKey	getConstrainedColumnsBitKey() Returns the BitKey for ALL columns (Measures and Levels) involved in the query.
List<Segment.ExcludedRegion>	getExcludedRegions()
SegmentHeader	getHeader()
RolapStar	getStar() Returns the star.
protected boolean	isExcluded(Object[] keys) Returns whether a cell value is excluded from this segment.
boolean	matches(AggregationKey aggregationKey, RolapStar.Measure measure)
void	print(PrintWriter pw) Prints the state of this Segment, including constraints and values.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

columns

protected final RolapStar.Column[] columns

This is set in the load method and is used during the processing of a particular aggregate load.

measure

public final RolapStar.Measure measure

predicates

public final StarColumnPredicate[] predicates

An array of axes, one for each constraining column, containing the values returned for that constraining column.

star

protected final RolapStar star

constrainedColumnsBitKey

protected final BitKey constrainedColumnsBitKey

excludedRegions

protected final List<Segment.ExcludedRegion> excludedRegions

List of regions to ignore when reading this segment. This list is populated when a region is flushed. The cells for these regions may be physically in the segment, because trimming segments can be expensive, but should still be ignored.

compoundPredicateList

protected final List<StarPredicate> compoundPredicateList

Constructor Detail

Segment

public Segment(RolapStar star,
               BitKey constrainedColumnsBitKey,
               RolapStar.Column[] columns,
               RolapStar.Measure measure,
               StarColumnPredicate[] predicates,
               List<Segment.ExcludedRegion> excludedRegions,
               List<StarPredicate> compoundPredicateList)

Creates a Segment; it's not loaded yet.

Parameters:

star - Star that this Segment belongs to

measure - Measure whose values this Segment contains

predicates - List of predicates constraining each axis

excludedRegions - List of regions which are not in this segment.

Method Detail

getColumns

public RolapStar.Column[] getColumns()

Returns the constrained columns.

getStar

public RolapStar getStar()

Returns the star.

getCompoundPredicateList

public List<StarPredicate> getCompoundPredicateList()

Returns the list of compound predicates.

getConstrainedColumnsBitKey

public BitKey getConstrainedColumnsBitKey()

Returns the BitKey for ALL columns (Measures and Levels) involved in the query.

describeAxes

protected void describeAxes(StringBuilder buf,
                            int i,
                            boolean values)

toString

public String toString()

Overrides:

toString in class Object

isExcluded

protected final boolean isExcluded(Object[] keys)

Returns whether a cell value is excluded from this segment.

print

public void print(PrintWriter pw)

Prints the state of this Segment, including constraints and values. Blocks the current thread until the segment is loaded.

Parameters:

pw - Writer

getExcludedRegions

public List<Segment.ExcludedRegion> getExcludedRegions()

matches

public boolean matches(AggregationKey aggregationKey,
                       RolapStar.Measure measure)

getHeader

public SegmentHeader getHeader()