saffron.rel.java
Class JavaAggregate

java.lang.Object
  |
  +--saffron.rel.Rel
        |
        +--saffron.rel.SingleRel
              |
              +--saffron.rel.Aggregate
                    |
                    +--saffron.rel.java.JavaAggregate

public class JavaAggregate

extends Aggregate

JavaAggregate implements the Aggregate relational operator by generating code. The code looks like this:

HashMap h = new HashMap();
 for each child
   HashableArray groups = new HashableArray(
     new Object[] {
   	 child.field4,
   	 child.field2});
   Object[] aggs = h.get(groups);
   if (aggs == null) {
     aggs = new Object[<>];
     aggs[0] = agg start code;
     aggs[1] = agg start code;
     h.put(groups, aggs);
   }
   agg inc code {aggs[0], childRow}
   agg inc code {aggs[1], childRow}
 end for
 Iterator keys = h.keys();
 while (keys.hasNext()) {
 	 T row = new T();
 	 HashableArray groups = (HashableArray) keys.next();
 	 row.c0 = groups[0];
 	 row.c1 = groups[1];
 	 Object[] aggs = h.get(groups);
 	 row.c2 = agg result code {aggs[0]}
 	 row.c3 = agg result code {aggs[1]}
   emit row to parent
 }

Simplifications:

• If there is onle one group column, the HashableArray is simplified to Object.
• If there is only one aggregate, the Object[] are simplified to Object.
• todo: Write an efficient implementation if there are no group columns.
• If there are no aggregations, JavaDistinct is more efficient.

Nested Class Summary

Nested classes inherited from class saffron.rel.Aggregate

Aggregate.Call

Nested classes inherited from class saffron.rel.Rel

Field Summary

(package private) Variable

var_h

Fields inherited from class saffron.rel.Aggregate

aggCalls, groupCount

Fields inherited from class saffron.rel.SingleRel

child

Fields inherited from class saffron.rel.Rel

cluster, digest, id, rowType

Constructor Summary

JavaAggregate(Cluster cluster, Rel child, int groupCount, Aggregate.Call[] aggCalls)

Method Summary

Object	clone()
Cost	computeSelfCost(Planner planner) Returns the cost of this plan (not including children).
CallingConvention	getConvention() Returns a value from CallingConvention.
Object	implement(Implementor implementor, int ordinal) Create a plan for this expression according to a calling convention.

Methods inherited from class saffron.rel.Aggregate

deriveRowType, getAggCalls, getGroupCount, register

Methods inherited from class saffron.rel.SingleRel

childrenAccept, explain, getInputs, replaceInput

Methods inherited from class saffron.rel.Rel

computeDigest, getChildExps, getCluster, getCorelVariable, getEnvironment, getId, getInput, getOrCreateCorelVariable, getParentEnv, getQualifier, getQuery, getRelTypeName, getRows, getRowType, getTable, getType, getVariablesStopped, implementExp, implementExps, implementFieldAccess, implementSelf, isAccessTo, isDistinct, onRegister, recomputeDigest, registerCorelVariable, setCorelVariable, toString

Methods inherited from class java.lang.Object

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

Field Detail

var_h

Variable var_h

Constructor Detail

JavaAggregate

public JavaAggregate(Cluster cluster,
                     Rel child,
                     int groupCount,
                     Aggregate.Call[] aggCalls)

Method Detail

clone

public Object clone()

Overrides:

clone in class Aggregate

getConvention

public CallingConvention getConvention()

Description copied from class: Rel

Returns a value from CallingConvention.

Overrides:

getConvention in class Rel

computeSelfCost

public Cost computeSelfCost(Planner planner)

Description copied from class: Rel

Returns the cost of this plan (not including children). The base implementation throws an error; derived classes should override.

Overrides:

computeSelfCost in class Aggregate

implement

public Object implement(Implementor implementor,
                        int ordinal)

Description copied from class: Rel

Create a plan for this expression according to a calling convention.

Overrides:

implement in class Rel

Parameters:

implementor - implementor

ordinal - indicates our position in the pre-, in- and postfix walk over the tree; ordinal is -1 when called from the parent, and i when called from the i^th child.