Aklakan commented on code in PR #2405:
URL: https://github.com/apache/jena/pull/2405#discussion_r1703989751
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jena-arq/src/main/java/org/apache/jena/sparql/engine/join/AbstractIterHashJoin.java:
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@@ -42,47 +42,52 @@ public abstract class AbstractIterHashJoin extends
QueryIter2 {
protected long s_countResults = 0 ; // Overall result size.
protected long s_trailerResults = 0 ; // Results from the
trailer iterator.
// See also stats in the probe table.
-
+
protected final JoinKey joinKey ;
- protected final HashProbeTable hashTable ;
+ protected final MultiHashProbeTable hashTable ;
private QueryIterator iterStream ;
private Binding rowStream = null ;
private Iterator<Binding> iterCurrent ;
- private boolean yielded ; // Flag to note when
current probe causes a result.
+ private boolean yielded ; // Flag to note when
current probe causes a result.
// Hanlde any "post join" additions.
private Iterator<Binding> iterTail = null ;
-
+
enum Phase { INIT, HASH , STREAM, TRAILER, DONE }
Phase state = Phase.INIT ;
-
+
private Binding slot = null ;
- protected AbstractIterHashJoin(JoinKey joinKey, QueryIterator probeIter,
QueryIterator streamIter, ExecutionContext execCxt) {
+ protected AbstractIterHashJoin(JoinKey initialJoinKey, QueryIterator
probeIter, QueryIterator streamIter, ExecutionContext execCxt) {
super(probeIter, streamIter, execCxt) ;
-
- if ( joinKey == null ) {
+
+ if ( initialJoinKey == null ) {
+ // This block computes an initial join key from the common
variables of each iterator's first binding.
+
QueryIterPeek pProbe = QueryIterPeek.create(probeIter, execCxt) ;
QueryIterPeek pStream = QueryIterPeek.create(streamIter, execCxt) ;
-
+
Binding bLeft = pProbe.peek() ;
Binding bRight = pStream.peek() ;
-
+
List<Var> varsLeft = Iter.toList(bLeft.vars()) ;
List<Var> varsRight = Iter.toList(bRight.vars()) ;
- joinKey = JoinKey.createVarKey(varsLeft, varsRight) ;
+ // joinKey = JoinKey.createVarKey(varsLeft, varsRight) ;
+ initialJoinKey = JoinKey.create(varsLeft, varsRight) ;
+
probeIter = pProbe ;
streamIter = pStream ;
}
-
- this.joinKey = joinKey ;
+
+ JoinKey maxJoinKey = null;
Review Comment:
The max join key was meant to prevent creation of JoinIndexes for other
variables than the given ones. For example, when set to [x, y] then an attempt
to create a JoinIndex for [x, y, z] would still only create one for [x, y] and
thus omit z. Most likely such a feature is not needed.
`initialJoinKey` improves over the original `joinKey`: Originally, only the
first variable common to the peeked bindings was used for indexing, now the all
common variables are used.
The `initialJoinKey` is used to store the probe-bindings directly in an
indexed structure (rather than e.g. a list), but the MultiHashProbe table can
create further `JoinIndex` instances depending on the lookup requests.
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