Revision: 4210
http://bigdata.svn.sourceforge.net/bigdata/?rev=4210&view=rev
Author: thompsonbry
Date: 2011-02-20 13:50:40 +0000 (Sun, 20 Feb 2011)
Log Message:
-----------
javadoc update on shared variables and constraints for the runtime optimizer.
Modified Paths:
--------------
branches/QUADS_QUERY_BRANCH/bigdata/src/java/com/bigdata/bop/controller/JoinGraph.java
Modified: branches/QUADS_QUERY_BRANCH/bigdata/src/java/com/bigdata/bop/controller/JoinGraph.java
===================================================================
--- branches/QUADS_QUERY_BRANCH/bigdata/src/java/com/bigdata/bop/controller/JoinGraph.java 2011-02-18 19:43:36 UTC (rev 4209)
+++ branches/QUADS_QUERY_BRANCH/bigdata/src/java/com/bigdata/bop/controller/JoinGraph.java 2011-02-20 13:50:40 UTC (rev 4210)
@@ -1950,36 +1950,42 @@
}
/*
- * Identify the edges by looking for shared variables among the
- * predicates.
+ * Create edges to represent possible joins between predicates based
+ * on directly shared variables.
*
- * Note: Variables appear in predicates or in constraints. Edges are
- * created to represent possible joins between predicates based on
- * those shared variables. There are two cases:
+ * Note: There are really three classes of joins to be considered.
*
- * (1) When the target predicate shares a variable with the source
- * predicate, then we always create an edge between those predicates
- * to represent a possible join.
+ * (1) The target predicate directly shares a variable with the
+ * source predicate. These joins are always constrained since the
+ * source predicate will have bound that variable.
*
* (2) When the source predicate shares a variable with a constraint
- * which also shares a variable with the target predicate, then we
- * will also create an edge to represent a possible join.
+ * which also shares a variable with the target predicate. While the
+ * predicates do not directly share a variable, these joins are
+ * constrained by the shared variable in the constraint on the
+ * target predicate. BSBM Q5 is an example of this case. We do not
+ * create edges for such joins here. Instead, we dynamically
+ * determine when a constrained join is possible when extending the
+ * join path in each round.
*
- * The second case handles the case where variables are transitively
- * shared through a constraint, but not directly shared between the
- * predicates. BSBM Q5 is an example of this case.
+ * (3) Any two predicates may always be joined. However, joins which
+ * do not share variables either directly or indirectly will be full
+ * cross products. Therefore such joins are run last and we do not
+ * create edges for them here.
*
- * Note: If applying these two rules fails to create any edges for
- * some vertex, then it does not share ANY variables and can be
- * paired with ANY of the other vertices. However, we always run
- * such vertices last as they can not restrict the cumulative
- * cardinality of the solutions. Such vertices are therefore
- * inserted into a separate set and appended to the join path once
- * all edges having shared variables have been exhausted.
+ * FIXME VERTICES WHICH SHARE VARS THROUGH A CONSTRAINT : handle
+ * dynamically rather than enumerating since the joins are path
+ * dependent.
*
- * FIXME VERTICES WHICH SHARE VARS THROUGH A CONSTRAINT.
- *
- * FIXME VERTICES WITH NO SHARED VARS.
+ * FIXME VERTICES WITH NO SHARED VARS : handle once all other joins
+ * have been exhausted. [These do not need to be collected, we just
+ * need to run them after all the constrained joins have been run.
+ * Also, these joins should not be sampled by the query optimizer
+ * since there is no reason to choose one ordering of these vertices
+ * over another. [The only reason to sample these joins would be
+ * to estimate the total cumulative cardinality of the join graph,
+ * which might be useful when estimating the run time or resource
+ * demand.]]
*/
{
@@ -3158,7 +3164,7 @@
* we are not yet handling anything except standard joins in the runtime
* optimizer.
*/
-
+
/**
* Execute the selected join path.
* <p>
This was sent by the SourceForge.net collaborative development platform, the world's largest Open Source development site.
|
