ControlledWorkerBoundJoin.java
/*******************************************************************************
* Copyright (c) 2019 Eclipse RDF4J contributors.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Distribution License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*******************************************************************************/
package org.eclipse.rdf4j.federated.evaluation.join;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Phaser;
import java.util.concurrent.TimeUnit;
import org.eclipse.rdf4j.common.iteration.CloseableIteration;
import org.eclipse.rdf4j.federated.FedXConfig;
import org.eclipse.rdf4j.federated.algebra.BoundJoinTupleExpr;
import org.eclipse.rdf4j.federated.algebra.CheckStatementPattern;
import org.eclipse.rdf4j.federated.algebra.FedXService;
import org.eclipse.rdf4j.federated.algebra.StatementTupleExpr;
import org.eclipse.rdf4j.federated.evaluation.FederationEvalStrategy;
import org.eclipse.rdf4j.federated.evaluation.concurrent.ControlledWorkerScheduler;
import org.eclipse.rdf4j.federated.evaluation.concurrent.ParallelExecutor;
import org.eclipse.rdf4j.federated.evaluation.concurrent.ParallelTask;
import org.eclipse.rdf4j.federated.structures.QueryInfo;
import org.eclipse.rdf4j.query.BindingSet;
import org.eclipse.rdf4j.query.QueryEvaluationException;
import org.eclipse.rdf4j.query.algebra.TupleExpr;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Execute the nested loop join in an asynchronous fashion, using grouped requests, i.e. group bindings into one SPARQL
* request using the UNION operator.
*
* The number of concurrent threads is controlled by a {@link ControlledWorkerScheduler} which works according to the
* FIFO principle and uses worker threads.
*
* This join cursor blocks until all scheduled tasks are finished, however the result iteration can be accessed from
* different threads to allow for pipelining.
*
* @author Andreas Schwarte
*
*/
public class ControlledWorkerBoundJoin extends ControlledWorkerJoin {
private static final Logger log = LoggerFactory.getLogger(ControlledWorkerBoundJoin.class);
public ControlledWorkerBoundJoin(ControlledWorkerScheduler<BindingSet> scheduler, FederationEvalStrategy strategy,
CloseableIteration<BindingSet, QueryEvaluationException> leftIter,
TupleExpr rightArg, BindingSet bindings, QueryInfo queryInfo)
throws QueryEvaluationException {
super(scheduler, strategy, leftIter, rightArg, bindings, queryInfo);
}
@Override
protected void handleBindings() throws Exception {
if (!(canApplyVectoredEvaluation(rightArg))) {
log.debug(
"Right argument is not an applicable BoundJoinTupleExpr. Fallback on ControlledWorkerJoin implementation: "
+ rightArg.getClass().getCanonicalName());
super.handleBindings(); // fallback
return;
}
int nBindingsCfg = this.queryInfo.getFederationContext().getConfig().getBoundJoinBlockSize();
int totalBindings = 0; // the total number of bindings
TupleExpr expr = rightArg;
TaskCreator taskCreator = null;
Phaser currentPhaser = phaser;
// first item is always sent in a non-bound way
if (!isClosed() && leftIter.hasNext()) {
BindingSet b = leftIter.next();
totalBindings++;
if (expr instanceof StatementTupleExpr) {
StatementTupleExpr stmt = (StatementTupleExpr) expr;
if (stmt.hasFreeVarsFor(b)) {
taskCreator = new BoundJoinTaskCreator(strategy, stmt);
} else {
expr = new CheckStatementPattern(stmt, queryInfo);
taskCreator = new CheckJoinTaskCreator(strategy, (CheckStatementPattern) expr);
}
} else if (expr instanceof FedXService) {
taskCreator = new FedXServiceJoinTaskCreator(strategy, (FedXService) expr);
} else {
throw new RuntimeException("Expr is of unexpected type: " + expr.getClass().getCanonicalName()
+ ". Please report this problem.");
}
currentPhaser.register();
scheduler.schedule(
new ParallelJoinTask(new PhaserHandlingParallelExecutor(this, currentPhaser), strategy, expr, b));
}
int nBindings;
List<BindingSet> bindings;
while (!isClosed() && leftIter.hasNext()) {
// create a new phaser if there are more than 10000 parties
// note: a phaser supports only up to 65535 registered parties
if (currentPhaser.getRegisteredParties() >= 10000) {
currentPhaser = new Phaser(currentPhaser);
}
/*
* XXX idea:
*
* make nBindings dependent on the number of intermediate results of the left argument.
*
* If many intermediate results, increase the number of bindings. This will result in less remote SPARQL
* requests.
*
*/
if (totalBindings > 10) {
nBindings = nBindingsCfg;
} else {
nBindings = 3;
}
bindings = new ArrayList<>(nBindings);
int count = 0;
while (!isClosed() && count < nBindings && leftIter.hasNext()) {
bindings.add(leftIter.next());
count++;
}
totalBindings += count;
currentPhaser.register();
scheduler.schedule(taskCreator.getTask(new PhaserHandlingParallelExecutor(this, currentPhaser), bindings));
}
leftIter.close();
scheduler.informFinish(this);
if (log.isDebugEnabled()) {
log.debug("JoinStats: left iter of " + getDisplayId() + " had " + totalBindings + " results.");
}
phaser.awaitAdvanceInterruptibly(phaser.arrive(), queryInfo.getMaxRemainingTimeMS(), TimeUnit.MILLISECONDS);
}
@Override
public void handleClose() throws QueryEvaluationException {
try {
super.handleClose();
} finally {
// signal the phaser to close (if currently being blocked)
phaser.forceTermination();
}
}
/**
* Returns true if the vectored evaluation can be applied for the join argument, i.e. there is no fallback to
* {@link ControlledWorkerJoin#handleBindings()}. This is
*
* a) if the expr is a {@link BoundJoinTupleExpr} (Mind the special handling for {@link FedXService} as defined in
* b) b) if the expr is a {@link FedXService} and {@link FedXConfig#getEnableServiceAsBoundJoin()}
*
* @return
*/
private boolean canApplyVectoredEvaluation(TupleExpr expr) {
if (expr instanceof BoundJoinTupleExpr) {
if (expr instanceof FedXService) {
return this.queryInfo.getFederationContext().getConfig().getEnableServiceAsBoundJoin();
}
return true;
}
return false;
}
protected interface TaskCreator {
ParallelTask<BindingSet> getTask(ParallelExecutor<BindingSet> control, List<BindingSet> bindings);
}
protected class BoundJoinTaskCreator implements TaskCreator {
protected final FederationEvalStrategy _strategy;
protected final StatementTupleExpr _expr;
public BoundJoinTaskCreator(
FederationEvalStrategy strategy, StatementTupleExpr expr) {
super();
_strategy = strategy;
_expr = expr;
}
@Override
public ParallelTask<BindingSet> getTask(ParallelExecutor<BindingSet> control, List<BindingSet> bindings) {
return new ParallelBoundJoinTask(control, _strategy, _expr, bindings);
}
}
protected class CheckJoinTaskCreator implements TaskCreator {
protected final FederationEvalStrategy _strategy;
protected final CheckStatementPattern _expr;
public CheckJoinTaskCreator(
FederationEvalStrategy strategy, CheckStatementPattern expr) {
super();
_strategy = strategy;
_expr = expr;
}
@Override
public ParallelTask<BindingSet> getTask(ParallelExecutor<BindingSet> control, List<BindingSet> bindings) {
return new ParallelCheckJoinTask(control, _strategy, _expr, bindings);
}
}
protected class FedXServiceJoinTaskCreator implements TaskCreator {
protected final FederationEvalStrategy _strategy;
protected final FedXService _expr;
public FedXServiceJoinTaskCreator(
FederationEvalStrategy strategy, FedXService expr) {
super();
_strategy = strategy;
_expr = expr;
}
@Override
public ParallelTask<BindingSet> getTask(ParallelExecutor<BindingSet> control, List<BindingSet> bindings) {
return new ParallelServiceJoinTask(control, _strategy, _expr, bindings);
}
}
}