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ARQ is a SPARQL 1.1 query engine for Apache Jena
/*
* Licensed to the Apache Software Foundation (ASF) under one
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* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
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*
* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.jena.sparql.algebra.optimize;
import org.apache.jena.query.ARQ ;
import org.apache.jena.sparql.ARQConstants ;
import org.apache.jena.sparql.SystemARQ ;
import org.apache.jena.sparql.algebra.* ;
import org.apache.jena.sparql.algebra.op.OpLabel ;
import org.apache.jena.sparql.util.Context ;
import org.apache.jena.sparql.util.Symbol ;
import org.slf4j.Logger ;
import org.slf4j.LoggerFactory ;
/** The standard optimization sequence. */
public class OptimizerStd implements Rewrite
{
static private Logger log = LoggerFactory.getLogger(Optimize.class) ;
private final Context context ;
public OptimizerStd(Context context) {
this.context = context ;
}
/** Alternative name for compatibility only */
public static final Symbol filterPlacementOldName = SystemARQ.allocSymbol("filterPlacement") ;
@Override
public Op rewrite(Op op) {
// Record optimizer
if ( context.get(ARQConstants.sysOptimizer) == null )
context.set(ARQConstants.sysOptimizer, this) ;
// Old name, new name fixup.
if ( context.isDefined(filterPlacementOldName) ) {
if ( context.isUndef(ARQ.optFilterPlacement) )
context.set(ARQ.optFilterPlacement, context.get(filterPlacementOldName)) ;
}
if ( false ) {
// Removal of "group of one" join (AKA SPARQL "simplification")
// is done during algebra generation in AlgebraGenerator
op = apply("Simplify", new TransformSimplify(), op) ;
op = apply("Delabel", new TransformRemoveLabels(), op) ;
}
// ** TransformScopeRename
// This is a requirement for the linearization execution that the default
// ARQ query engine uses where possible.
// This transformation must be done (e.g. by QueryEngineBase) if no other optimization is done.
op = TransformScopeRename.transform(op) ;
// Prepare expressions.
OpWalker.walk(op, new OpVisitorExprPrepare(context)) ;
// Convert paths to triple patterns if possible.
if ( context.isTrueOrUndef(ARQ.optPathFlatten) ) {
op = apply("Path flattening", new TransformPathFlattern(), op) ;
// and merge adjacent BGPs (part 1)
if ( context.isTrueOrUndef(ARQ.optMergeBGPs) )
op = apply("Merge BGPs", new TransformMergeBGPs(), op) ;
}
// Having done the required transforms, specifically TransformScopeRename,
// do each optimization via an overrideable method. Subclassing can modify the
// transform performed.
// Expression constant folding
if ( context.isTrueOrUndef(ARQ.optExprConstantFolding) )
op = transformExprConstantFolding(op) ;
if ( context.isTrueOrUndef(ARQ.propertyFunctions) )
op = transformPropertyFunctions(op) ;
// Expand (A&&B) to two filter (A), (B) so that they can be placed independently.
if ( context.isTrueOrUndef(ARQ.optFilterConjunction) )
op = transformFilterConjunction(op) ;
// Expand IN and NOT IN which then allows other optimizations to be applied.
if ( context.isTrueOrUndef(ARQ.optFilterExpandOneOf) )
op = transformFilterExpandOneOf(op) ;
// Eliminate/Inline assignments where possible
// Do this before we do some of the filter transformation work as inlining assignments
// may give us more flexibility in optimizing the resulting filters
if ( context.isTrue(ARQ.optInlineAssignments) )
op = transformInlineAssignments(op) ;
// Apply some general purpose filter transformations
if ( context.isTrueOrUndef(ARQ.optFilterImplicitJoin) )
op = transformFilterImplicitJoin(op) ;
if ( context.isTrueOrUndef(ARQ.optImplicitLeftJoin) )
op = transformFilterImplicitLeftJoin(op) ;
if ( context.isTrueOrUndef(ARQ.optFilterDisjunction) )
op = transformFilterDisjunction(op) ;
// Some ORDER BY-LIMIT N queries can be done more efficiently by only recording
// the top N items, so a full sort is not needed.
if ( context.isTrueOrUndef(ARQ.optTopNSorting) )
op = transformTopNSorting(op) ;
// ORDER BY+DISTINCT optimizations
// We apply the one that changes evaluation order first since when it does apply it will give much
// better performance than just transforming DISTINCT to REDUCED
if ( context.isTrueOrUndef(ARQ.optOrderByDistinctApplication) )
op = transformOrderByDistinctApplication(op) ;
// Transform some DISTINCT to REDUCED, slightly more liberal transform that ORDER BY+DISTINCT application
// Reduces memory consumption.
if ( context.isTrueOrUndef(ARQ.optDistinctToReduced) )
op = transformDistinctToReduced(op) ;
// Find joins/leftJoin that can be done by index joins (generally preferred as fixed memory overhead).
if ( context.isTrueOrUndef(ARQ.optIndexJoinStrategy) )
op = transformJoinStrategy(op) ;
// Place filters close to where their dependency variables are defined.
// This prunes the output of that step as early as possible.
// If done before TransformJoinStrategy, you can get two applications
// of a filter in a (sequence) from each half of a (join). This is harmless,
// because filters are generally cheap, but it looks a bit bad.
if ( context.isTrueOrUndef(ARQ.optFilterPlacement) )
op = transformFilterPlacement(op) ;
// Replace suitable FILTER(?x = TERM) with (assign) and write the TERM for ?x in the pattern.
// Apply (possible a second time) after FILTER placement as it can create new possibilities.
// See JENA-616.
if ( context.isTrueOrUndef(ARQ.optFilterEquality) )
op = transformFilterEquality(op) ;
// Replace suitable FILTER(?x != TERM) with (minus (original) (table)) where the table contains
// the candidate rows to be eliminated
// Off by default due to minimal performance difference
if ( context.isTrue(ARQ.optFilterInequality) )
op = transformFilterInequality(op) ;
// Promote table empty as late as possible since this will only be produced by other
// optimizations and never directly from algebra generation
if ( context.isTrueOrUndef(ARQ.optPromoteTableEmpty) )
op = transformPromoteTableEmpty(op) ;
// Merge adjacent BGPs
if ( context.isTrueOrUndef(ARQ.optMergeBGPs) )
op = transformMergeBGPs(op) ;
// Normally, leave to the specific engines.
if ( context.isTrue(ARQ.optReorderBGP) )
op = transformReorder(op) ;
// Merge (extend) and (assign) stacks
if ( context.isTrueOrUndef(ARQ.optMergeExtends) )
op = transformExtendCombine(op) ;
// Mark
if ( false )
op = OpLabel.create("Transformed", op) ;
return op ;
}
protected Op transformExprConstantFolding(Op op) {
return Transformer.transform(new TransformCopy(), new ExprTransformConstantFold(), op);
}
protected Op transformPropertyFunctions(Op op) {
return apply("Property Functions", new TransformPropertyFunction(context), op) ;
}
protected Op transformFilterConjunction(Op op) {
return apply("filter conjunctions to ExprLists", new TransformFilterConjunction(), op) ;
}
protected Op transformFilterExpandOneOf(Op op) {
return apply("Break up IN and NOT IN", new TransformExpandOneOf(), op) ;
}
protected Op transformInlineAssignments(Op op) {
return TransformEliminateAssignments.eliminate(op, context.isTrue(ARQ.optInlineAssignmentsAggressive));
}
protected Op transformFilterImplicitJoin(Op op) {
return apply("Filter Implicit Join", new TransformFilterImplicitJoin(), op);
}
protected Op transformFilterImplicitLeftJoin(Op op) {
return apply("Implicit Left Join", new TransformImplicitLeftJoin(), op);
}
protected Op transformFilterDisjunction(Op op) {
return apply("Filter Disjunction", new TransformFilterDisjunction(), op) ;
}
protected Op transformTopNSorting(Op op) {
return apply("TopN Sorting", new TransformTopN(), op) ;
}
protected Op transformOrderByDistinctApplication(Op op) {
return apply("Apply DISTINCT prior to ORDER BY where possible", new TransformOrderByDistinctApplication(), op);
}
protected Op transformDistinctToReduced(Op op) {
return apply("Distinct replaced with reduced", new TransformDistinctToReduced(), op) ;
}
protected Op transformJoinStrategy(Op op) {
return apply("Index Join strategy", new TransformJoinStrategy(), op) ;
}
protected Op transformFilterPlacement(Op op) {
if ( context.isTrue(ARQ.optFilterPlacementConservative))
op = apply("Filter Placement (conservative)", new TransformFilterPlacementConservative(), op) ;
else {
// Whether to push into BGPs
boolean b = context.isTrueOrUndef(ARQ.optFilterPlacementBGP) ;
op = apply("Filter Placement", new TransformFilterPlacement(b), op) ;
}
return op ;
}
protected Op transformFilterEquality(Op op) {
return apply("Filter Equality", new TransformFilterEquality(), op) ;
}
protected Op transformFilterInequality(Op op) {
return apply("Filter Inequality", new TransformFilterInequality(), op);
}
protected Op transformPromoteTableEmpty(Op op) {
return apply("Table Empty Promotion", new TransformPromoteTableEmpty(), op) ;
}
protected Op transformMergeBGPs(Op op) {
return apply("Merge BGPs", new TransformMergeBGPs(), op) ;
}
protected Op transformReorder(Op op) {
return apply("ReorderMerge BGPs", new TransformReorder(), op) ;
}
protected Op transformExtendCombine(Op op) {
return apply("Combine BIND/LET", new TransformExtendCombine(), op) ;
}
public static Op apply(Transform transform, Op op) {
Op op2 = Transformer.transformSkipService(transform, op) ;
if ( op2 != op )
return op2 ;
return op ;
}
public static Op apply(String label, Transform transform, Op op) {
Op op2 = Transformer.transformSkipService(transform, op) ;
final boolean debug = false ;
if ( debug ) {
if ( label != null && log.isInfoEnabled() )
log.info("Transform: " + label) ;
if ( op == op2 ) {
if ( log.isInfoEnabled() )
log.info("No change (==)") ;
return op2 ;
}
if ( op.equals(op2) ) {
if ( log.isInfoEnabled() )
log.info("No change (equals)") ;
return op2 ;
}
if ( log.isInfoEnabled() ) {
log.info("\n" + op.toString()) ;
log.info("\n" + op2.toString()) ;
}
}
if ( op2 != op )
return op2 ;
return op ;
}
}