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/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hive.ql.parse;
import static org.apache.hadoop.hive.ql.plan.ReduceSinkDesc.ReducerTraits.AUTOPARALLEL;
import java.util.*;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hive.conf.HiveConf;
import org.apache.hadoop.hive.ql.exec.AppMasterEventOperator;
import org.apache.hadoop.hive.ql.exec.FetchTask;
import org.apache.hadoop.hive.ql.exec.FileSinkOperator;
import org.apache.hadoop.hive.ql.exec.FilterOperator;
import org.apache.hadoop.hive.ql.exec.HashTableDummyOperator;
import org.apache.hadoop.hive.ql.exec.MapJoinOperator;
import org.apache.hadoop.hive.ql.exec.Operator;
import org.apache.hadoop.hive.ql.exec.OperatorUtils;
import org.apache.hadoop.hive.ql.exec.ReduceSinkOperator;
import org.apache.hadoop.hive.ql.exec.SerializationUtilities;
import org.apache.hadoop.hive.ql.exec.TableScanOperator;
import org.apache.hadoop.hive.ql.exec.UnionOperator;
import org.apache.hadoop.hive.ql.exec.Utilities;
import org.apache.hadoop.hive.ql.lib.*;
import org.apache.hadoop.hive.ql.optimizer.GenMapRedUtils;
import org.apache.hadoop.hive.ql.plan.*;
import org.apache.hadoop.hive.ql.plan.TezEdgeProperty.EdgeType;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDFBetween;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDFInBloomFilter;
import org.apache.hadoop.hive.serde2.typeinfo.TypeInfoFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.google.common.collect.BiMap;
import com.google.common.collect.HashBiMap;
/**
* GenTezUtils is a collection of shared helper methods to produce TezWork.
* All the methods in this class should be static, but some aren't; this is to facilitate testing.
* Methods are made non-static on as needed basis.
*/
public class GenTezUtils {
static final private Logger LOG = LoggerFactory.getLogger(GenTezUtils.class);
public GenTezUtils() {
}
public static UnionWork createUnionWork(
GenTezProcContext context, Operator root, Operator leaf, TezWork tezWork) {
UnionWork unionWork = new UnionWork("Union "+ context.nextSequenceNumber());
context.rootUnionWorkMap.put(root, unionWork);
context.unionWorkMap.put(leaf, unionWork);
tezWork.add(unionWork);
return unionWork;
}
public static ReduceWork createReduceWork(
GenTezProcContext context, Operator root, TezWork tezWork) {
assert !root.getParentOperators().isEmpty();
boolean isAutoReduceParallelism =
context.conf.getBoolVar(HiveConf.ConfVars.TEZ_AUTO_REDUCER_PARALLELISM);
float maxPartitionFactor =
context.conf.getFloatVar(HiveConf.ConfVars.TEZ_MAX_PARTITION_FACTOR);
float minPartitionFactor = context.conf.getFloatVar(HiveConf.ConfVars.TEZ_MIN_PARTITION_FACTOR);
long bytesPerReducer = context.conf.getLongVar(HiveConf.ConfVars.BYTESPERREDUCER);
ReduceWork reduceWork = new ReduceWork(Utilities.REDUCENAME + context.nextSequenceNumber());
LOG.debug("Adding reduce work (" + reduceWork.getName() + ") for " + root);
reduceWork.setReducer(root);
reduceWork.setNeedsTagging(GenMapRedUtils.needsTagging(reduceWork));
// All parents should be reduce sinks. We pick the one we just walked
// to choose the number of reducers. In the join/union case they will
// all be -1. In sort/order case where it matters there will be only
// one parent.
assert context.parentOfRoot instanceof ReduceSinkOperator;
ReduceSinkOperator reduceSink = (ReduceSinkOperator) context.parentOfRoot;
reduceWork.setNumReduceTasks(reduceSink.getConf().getNumReducers());
if (isAutoReduceParallelism && reduceSink.getConf().getReducerTraits().contains(AUTOPARALLEL)) {
// configured limit for reducers
final int maxReducers = context.conf.getIntVar(HiveConf.ConfVars.MAXREDUCERS);
// estimated number of reducers
final int nReducers = reduceSink.getConf().getNumReducers();
// min we allow tez to pick
int minPartition = Math.max(1, (int) (nReducers * minPartitionFactor));
minPartition = (minPartition > maxReducers) ? maxReducers : minPartition;
// max we allow tez to pick
int maxPartition = Math.max(1, (int) (nReducers * maxPartitionFactor));
maxPartition = (maxPartition > maxReducers) ? maxReducers : maxPartition;
// reduce only if the parameters are significant
if (minPartition < maxPartition &&
nReducers * minPartitionFactor >= 1.0) {
reduceWork.setAutoReduceParallelism(true);
reduceWork.setMinReduceTasks(minPartition);
reduceWork.setMaxReduceTasks(maxPartition);
} else if (nReducers < maxPartition) {
// the max is good, the min is too low
reduceWork.setNumReduceTasks(maxPartition);
}
}
setupReduceSink(context, reduceWork, reduceSink);
tezWork.add(reduceWork);
TezEdgeProperty edgeProp;
EdgeType edgeType = determineEdgeType(context.preceedingWork, reduceWork, reduceSink);
if (reduceWork.isAutoReduceParallelism()) {
edgeProp =
new TezEdgeProperty(context.conf, edgeType, true,
reduceWork.getMinReduceTasks(), reduceWork.getMaxReduceTasks(), bytesPerReducer);
} else {
edgeProp = new TezEdgeProperty(edgeType);
}
tezWork.connect(
context.preceedingWork,
reduceWork, edgeProp);
context.connectedReduceSinks.add(reduceSink);
return reduceWork;
}
private static void setupReduceSink(
GenTezProcContext context, ReduceWork reduceWork, ReduceSinkOperator reduceSink) {
LOG.debug("Setting up reduce sink: " + reduceSink
+ " with following reduce work: " + reduceWork.getName());
// need to fill in information about the key and value in the reducer
GenMapRedUtils.setKeyAndValueDesc(reduceWork, reduceSink);
// remember which parent belongs to which tag
int tag = reduceSink.getConf().getTag();
reduceWork.getTagToInput().put(tag == -1 ? 0 : tag,
context.preceedingWork.getName());
// remember the output name of the reduce sink
reduceSink.getConf().setOutputName(reduceWork.getName());
}
public MapWork createMapWork(GenTezProcContext context, Operator root,
TezWork tezWork, PrunedPartitionList partitions) throws SemanticException {
assert root.getParentOperators().isEmpty();
MapWork mapWork = new MapWork(Utilities.MAPNAME + context.nextSequenceNumber());
LOG.debug("Adding map work (" + mapWork.getName() + ") for " + root);
// map work starts with table scan operators
assert root instanceof TableScanOperator;
TableScanOperator ts = (TableScanOperator) root;
String alias = ts.getConf().getAlias();
setupMapWork(mapWork, context, partitions, ts, alias);
if (ts.getConf().getTableMetadata() != null && ts.getConf().getTableMetadata().isDummyTable()) {
mapWork.setDummyTableScan(true);
}
if (ts.getConf().getNumBuckets() > 0) {
mapWork.setIncludedBuckets(ts.getConf().getIncludedBuckets());
}
// add new item to the tez work
tezWork.add(mapWork);
return mapWork;
}
// this method's main use is to help unit testing this class
protected void setupMapWork(MapWork mapWork, GenTezProcContext context,
PrunedPartitionList partitions, TableScanOperator root,
String alias) throws SemanticException {
// All the setup is done in GenMapRedUtils
GenMapRedUtils.setMapWork(mapWork, context.parseContext,
context.inputs, partitions, root, alias, context.conf, false);
// we also collect table stats while collecting column stats.
if (context.parseContext.getAnalyzeRewrite() != null) {
mapWork.setGatheringStats(true);
}
}
// removes any union operator and clones the plan
public static void removeUnionOperators(GenTezProcContext context, BaseWork work, int indexForTezUnion)
throws SemanticException {
List> roots = new ArrayList>();
roots.addAll(work.getAllRootOperators());
if (work.getDummyOps() != null) {
roots.addAll(work.getDummyOps());
}
roots.addAll(context.eventOperatorSet);
// need to clone the plan.
List> newRoots = SerializationUtilities.cloneOperatorTree(roots, indexForTezUnion);
// we're cloning the operator plan but we're retaining the original work. That means
// that root operators have to be replaced with the cloned ops. The replacement map
// tells you what that mapping is.
BiMap, Operator> replacementMap = HashBiMap.create();
// there's some special handling for dummyOps required. Mapjoins won't be properly
// initialized if their dummy parents aren't initialized. Since we cloned the plan
// we need to replace the dummy operators in the work with the cloned ones.
List dummyOps = new LinkedList();
Iterator> it = newRoots.iterator();
for (Operator orig: roots) {
Set fsOpSet = OperatorUtils.findOperators(orig, FileSinkOperator.class);
for (FileSinkOperator fsOp : fsOpSet) {
context.fileSinkSet.remove(fsOp);
}
Operator newRoot = it.next();
replacementMap.put(orig, newRoot);
if (newRoot instanceof HashTableDummyOperator) {
// dummy ops need to be updated to the cloned ones.
dummyOps.add((HashTableDummyOperator) newRoot);
it.remove();
} else if (newRoot instanceof AppMasterEventOperator) {
// event operators point to table scan operators. When cloning these we
// need to restore the original scan.
if (newRoot.getConf() instanceof DynamicPruningEventDesc) {
TableScanOperator ts = ((DynamicPruningEventDesc) orig.getConf()).getTableScan();
if (ts == null) {
throw new AssertionError("No table scan associated with dynamic event pruning. " + orig);
}
((DynamicPruningEventDesc) newRoot.getConf()).setTableScan(ts);
}
it.remove();
} else {
if (newRoot instanceof TableScanOperator) {
if (context.tsToEventMap.containsKey(orig)) {
// we need to update event operators with the cloned table scan
for (AppMasterEventOperator event : context.tsToEventMap.get(orig)) {
((DynamicPruningEventDesc) event.getConf()).setTableScan((TableScanOperator) newRoot);
}
}
// This TableScanOperator could be part of semijoin optimization.
Map rsOpToTsOpMap =
context.parseContext.getRsOpToTsOpMap();
for (ReduceSinkOperator rs : rsOpToTsOpMap.keySet()) {
if (rsOpToTsOpMap.get(rs) == orig) {
rsOpToTsOpMap.put(rs, (TableScanOperator) newRoot);
}
}
}
context.rootToWorkMap.remove(orig);
context.rootToWorkMap.put(newRoot, work);
}
}
// now we remove all the unions. we throw away any branch that's not reachable from
// the current set of roots. The reason is that those branches will be handled in
// different tasks.
Deque> operators = new LinkedList>();
operators.addAll(newRoots);
Set> seen = new HashSet>();
while(!operators.isEmpty()) {
Operator current = operators.pop();
seen.add(current);
if (current instanceof FileSinkOperator) {
FileSinkOperator fileSink = (FileSinkOperator)current;
// remember it for additional processing later
context.fileSinkSet.add(fileSink);
FileSinkDesc desc = fileSink.getConf();
Path path = desc.getDirName();
List linked;
if (!context.linkedFileSinks.containsKey(path)) {
linked = new ArrayList();
context.linkedFileSinks.put(path, linked);
}
linked = context.linkedFileSinks.get(path);
linked.add(desc);
desc.setDirName(new Path(path, "" + linked.size()));
desc.setLinkedFileSink(true);
desc.setParentDir(path);
desc.setLinkedFileSinkDesc(linked);
}
if (current instanceof AppMasterEventOperator) {
// remember for additional processing later
context.eventOperatorSet.add((AppMasterEventOperator) current);
// mark the original as abandoned. Don't need it anymore.
context.abandonedEventOperatorSet.add((AppMasterEventOperator) replacementMap.inverse()
.get(current));
}
if (current instanceof UnionOperator) {
Operator parent = null;
int count = 0;
for (Operator op: current.getParentOperators()) {
if (seen.contains(op)) {
++count;
parent = op;
}
}
// we should have been able to reach the union from only one side.
assert count <= 1;
if (parent == null) {
// root operator is union (can happen in reducers)
replacementMap.put(current, current.getChildOperators().get(0));
} else {
parent.removeChildAndAdoptItsChildren(current);
}
}
if (current instanceof FileSinkOperator
|| current instanceof ReduceSinkOperator) {
current.setChildOperators(null);
} else {
operators.addAll(current.getChildOperators());
}
}
LOG.debug("Setting dummy ops for work " + work.getName() + ": " + dummyOps);
work.setDummyOps(dummyOps);
work.replaceRoots(replacementMap);
}
public static void processFileSink(GenTezProcContext context, FileSinkOperator fileSink)
throws SemanticException {
ParseContext parseContext = context.parseContext;
boolean isInsertTable = // is INSERT OVERWRITE TABLE
GenMapRedUtils.isInsertInto(parseContext, fileSink);
HiveConf hconf = parseContext.getConf();
boolean chDir = GenMapRedUtils.isMergeRequired(context.moveTask,
hconf, fileSink, context.currentTask, isInsertTable);
Path finalName = GenMapRedUtils.createMoveTask(context.currentTask,
chDir, fileSink, parseContext, context.moveTask, hconf, context.dependencyTask);
if (chDir) {
// Merge the files in the destination table/partitions by creating Map-only merge job
// If underlying data is RCFile or OrcFile, RCFileBlockMerge task or
// OrcFileStripeMerge task would be created.
LOG.info("using CombineHiveInputformat for the merge job");
GenMapRedUtils.createMRWorkForMergingFiles(fileSink, finalName,
context.dependencyTask, context.moveTask,
hconf, context.currentTask);
}
FetchTask fetchTask = parseContext.getFetchTask();
if (fetchTask != null && context.currentTask.getNumChild() == 0) {
if (fetchTask.isFetchFrom(fileSink.getConf())) {
context.currentTask.setFetchSource(true);
}
}
}
/**
* processAppMasterEvent sets up the event descriptor and the MapWork.
*
* @param procCtx
* @param event
*/
public static void processAppMasterEvent(
GenTezProcContext procCtx, AppMasterEventOperator event) {
if (procCtx.abandonedEventOperatorSet.contains(event)) {
// don't need this anymore
return;
}
DynamicPruningEventDesc eventDesc = (DynamicPruningEventDesc)event.getConf();
TableScanOperator ts = eventDesc.getTableScan();
MapWork work = (MapWork) procCtx.rootToWorkMap.get(ts);
if (work == null) {
throw new AssertionError("No work found for tablescan " + ts);
}
BaseWork enclosingWork = getEnclosingWork(event, procCtx);
if (enclosingWork == null) {
throw new AssertionError("Cannot find work for operator" + event);
}
String sourceName = enclosingWork.getName();
// store the vertex name in the operator pipeline
eventDesc.setVertexName(work.getName());
eventDesc.setInputName(work.getAliases().get(0));
// store table descriptor in map-work
if (!work.getEventSourceTableDescMap().containsKey(sourceName)) {
work.getEventSourceTableDescMap().put(sourceName, new LinkedList());
}
List tables = work.getEventSourceTableDescMap().get(sourceName);
tables.add(event.getConf().getTable());
// store column name in map-work
if (!work.getEventSourceColumnNameMap().containsKey(sourceName)) {
work.getEventSourceColumnNameMap().put(sourceName, new LinkedList());
}
List columns = work.getEventSourceColumnNameMap().get(sourceName);
columns.add(eventDesc.getTargetColumnName());
if (!work.getEventSourceColumnTypeMap().containsKey(sourceName)) {
work.getEventSourceColumnTypeMap().put(sourceName, new LinkedList());
}
List columnTypes = work.getEventSourceColumnTypeMap().get(sourceName);
columnTypes.add(eventDesc.getTargetColumnType());
// store partition key expr in map-work
if (!work.getEventSourcePartKeyExprMap().containsKey(sourceName)) {
work.getEventSourcePartKeyExprMap().put(sourceName, new LinkedList());
}
List keys = work.getEventSourcePartKeyExprMap().get(sourceName);
keys.add(eventDesc.getPartKey());
}
/**
* getEncosingWork finds the BaseWork any given operator belongs to.
*/
public static BaseWork getEnclosingWork(Operator op, GenTezProcContext procCtx) {
List> ops = new ArrayList>();
findRoots(op, ops);
for (Operator r : ops) {
BaseWork work = procCtx.rootToWorkMap.get(r);
if (work != null) {
return work;
}
}
return null;
}
/*
* findRoots returns all root operators (in ops) that result in operator op
*/
private static void findRoots(Operator op, List> ops) {
List> parents = op.getParentOperators();
if (parents == null || parents.isEmpty()) {
ops.add(op);
return;
}
for (Operator p : parents) {
findRoots(p, ops);
}
}
/**
* Remove an operator branch. When we see a fork, we know it's time to do the removal.
* @param event the leaf node of which branch to be removed
*/
public static void removeBranch(Operator event) {
Operator child = event;
Operator curr = event;
while (curr.getChildOperators().size() <= 1) {
child = curr;
curr = curr.getParentOperators().get(0);
}
curr.removeChild(child);
}
public static EdgeType determineEdgeType(BaseWork preceedingWork, BaseWork followingWork, ReduceSinkOperator reduceSinkOperator) {
if (followingWork instanceof ReduceWork) {
// Ideally there should be a better way to determine that the followingWork contains
// a dynamic partitioned hash join, but in some cases (createReduceWork()) it looks like
// the work must be created/connected first, before the GenTezProcContext can be updated
// with the mapjoin/work relationship.
ReduceWork reduceWork = (ReduceWork) followingWork;
if (reduceWork.getReducer() instanceof MapJoinOperator) {
MapJoinOperator joinOp = (MapJoinOperator) reduceWork.getReducer();
if (joinOp.getConf().isDynamicPartitionHashJoin()) {
return EdgeType.CUSTOM_SIMPLE_EDGE;
}
}
}
if(!reduceSinkOperator.getConf().isOrdering()) {
//if no sort keys are specified, use an edge that does not sort
return EdgeType.CUSTOM_SIMPLE_EDGE;
}
return EdgeType.SIMPLE_EDGE;
}
public static void processDynamicMinMaxPushDownOperator(
GenTezProcContext procCtx, RuntimeValuesInfo runtimeValuesInfo,
ReduceSinkOperator rs)
throws SemanticException {
TableScanOperator ts = procCtx.parseContext.getRsOpToTsOpMap().get(rs);
List rsWorkList = procCtx.childToWorkMap.get(rs);
if (ts == null || rsWorkList == null) {
// This happens when the ReduceSink's edge has been removed by cycle
// detection logic. Nothing to do here.
return;
}
LOG.debug("ResduceSink " + rs + " to TableScan " + ts);
if (rsWorkList.size() != 1) {
StringBuilder sb = new StringBuilder();
for (BaseWork curWork : rsWorkList) {
if ( sb.length() > 0) {
sb.append(", ");
}
sb.append(curWork.getName());
}
throw new SemanticException(rs + " belongs to multiple BaseWorks: " + sb.toString());
}
BaseWork parentWork = rsWorkList.get(0);
BaseWork childWork = procCtx.rootToWorkMap.get(ts);
// Connect parent/child work with a brodacast edge.
LOG.debug("Connecting Baswork - " + parentWork.getName() + " to " + childWork.getName());
TezEdgeProperty edgeProperty = new TezEdgeProperty(EdgeType.BROADCAST_EDGE);
TezWork tezWork = procCtx.currentTask.getWork();
tezWork.connect(parentWork, childWork, edgeProperty);
// Set output names in ReduceSink
rs.getConf().setOutputName(childWork.getName());
// Set up the dynamic values in the childWork.
RuntimeValuesInfo childRuntimeValuesInfo =
new RuntimeValuesInfo();
childRuntimeValuesInfo.setTableDesc(runtimeValuesInfo.getTableDesc());
childRuntimeValuesInfo.setDynamicValueIDs(runtimeValuesInfo.getDynamicValueIDs());
childRuntimeValuesInfo.setColExprs(runtimeValuesInfo.getColExprs());
childWork.setInputSourceToRuntimeValuesInfo(
parentWork.getName(), childRuntimeValuesInfo);
}
// Functionality to remove semi-join optimization
public static void removeSemiJoinOperator(ParseContext context,
ReduceSinkOperator rs,
TableScanOperator ts) throws SemanticException{
// Cleanup the synthetic predicate in the tablescan operator by
// replacing it with "true"
LOG.debug("Removing ReduceSink " + rs + " and TableScan " + ts);
ExprNodeDesc constNode = new ExprNodeConstantDesc(
TypeInfoFactory.booleanTypeInfo, Boolean.TRUE);
DynamicValuePredicateContext filterDynamicValuePredicatesCollection =
new DynamicValuePredicateContext();
FilterDesc filterDesc = ((FilterOperator)(ts.getChildOperators().get(0))).getConf();
collectDynamicValuePredicates(filterDesc.getPredicate(),
filterDynamicValuePredicatesCollection);
for (ExprNodeDesc nodeToRemove : filterDynamicValuePredicatesCollection
.childParentMapping.keySet()) {
// Find out if this synthetic predicate belongs to the current cycle
boolean skip = true;
for (ExprNodeDesc expr : nodeToRemove.getChildren()) {
if (expr instanceof ExprNodeDynamicValueDesc ) {
String dynamicValueIdFromExpr = ((ExprNodeDynamicValueDesc) expr)
.getDynamicValue().getId();
List dynamicValueIdsFromMap = context.
getRsToRuntimeValuesInfoMap().get(rs).getDynamicValueIDs();
for (String dynamicValueIdFromMap : dynamicValueIdsFromMap) {
if (dynamicValueIdFromExpr.equals(dynamicValueIdFromMap)) {
// Intended predicate to be removed
skip = false;
break;
}
}
}
}
if (!skip) {
ExprNodeDesc nodeParent = filterDynamicValuePredicatesCollection
.childParentMapping.get(nodeToRemove);
if (nodeParent == null) {
// This was the only predicate, set filter expression to const
filterDesc.setPredicate(constNode);
} else {
int i = nodeParent.getChildren().indexOf(nodeToRemove);
nodeParent.getChildren().remove(i);
nodeParent.getChildren().add(i, constNode);
}
// skip the rest of the predicates
skip = true;
}
}
context.getRsOpToTsOpMap().remove(rs);
}
private static class DynamicValuePredicateContext implements NodeProcessorCtx {
HashMap childParentMapping = new HashMap();
}
private static class DynamicValuePredicateProc implements NodeProcessor {
@Override
public Object process(Node nd, Stack stack, NodeProcessorCtx procCtx,
Object... nodeOutputs) throws SemanticException {
DynamicValuePredicateContext ctx = (DynamicValuePredicateContext) procCtx;
ExprNodeDesc parent = (ExprNodeDesc) stack.get(stack.size() - 2);
if (parent instanceof ExprNodeGenericFuncDesc) {
ExprNodeGenericFuncDesc parentFunc = (ExprNodeGenericFuncDesc) parent;
if (parentFunc.getGenericUDF() instanceof GenericUDFBetween ||
parentFunc.getGenericUDF() instanceof GenericUDFInBloomFilter) {
ExprNodeDesc grandParent = stack.size() >= 3 ?
(ExprNodeDesc) stack.get(stack.size() - 3) : null;
ctx.childParentMapping.put(parentFunc, grandParent);
}
}
return null;
}
}
private static void collectDynamicValuePredicates(ExprNodeDesc pred, NodeProcessorCtx ctx) throws SemanticException {
// create a walker which walks the tree in a DFS manner while maintaining
// the operator stack. The dispatcher
// generates the plan from the operator tree
Map exprRules = new LinkedHashMap();
exprRules.put(new RuleRegExp("R1", ExprNodeDynamicValueDesc.class.getName() + "%"), new DynamicValuePredicateProc());
Dispatcher disp = new DefaultRuleDispatcher(null, exprRules, ctx);
GraphWalker egw = new DefaultGraphWalker(disp);
List startNodes = new ArrayList();
startNodes.add(pred);
egw.startWalking(startNodes, null);
}
}
