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Set collection mode to breadth_first in the terms aggregation when the cardinality of the field is unknown or smaller than the requested size. 

closes #9825
This commit is contained in:
Jim Ferenczi 2016-06-08 12:46:11 +02:00
parent 01004c72ba
commit ad232aebbe
5 changed files with 101 additions and 23 deletions
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14
core/src/main/java/org/elasticsearch/search/aggregations/bucket/BestBucketsDeferringCollector.java
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@ -166,16 +166,16 @@ public class BestBucketsDeferringCollector extends DeferringBucketCollector {
int doc = 0;
for (long i = 0, end = entry.docDeltas.size(); i < end; ++i) {
doc += docDeltaIterator.next();
if (needsScores) {
if (docIt.docID() < doc) {
docIt.advance(doc);
}
// aggregations should only be replayed on matching documents
assert docIt.docID() == doc;
}
final long bucket = buckets.next();
final long rebasedBucket = hash.find(bucket);
if (rebasedBucket != -1) {
if (needsScores) {
if (docIt.docID() < doc) {
docIt.advance(doc);
}
// aggregations should only be replayed on matching documents
assert docIt.docID() == doc;
}
leafCollector.collect(doc, rebasedBucket);
}
}

10
core/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregationBuilder.java
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@ -56,7 +56,7 @@ public class TermsAggregationBuilder extends ValuesSourceAggregationBuilder<Valu
private Terms.Order order = Terms.Order.compound(Terms.Order.count(false), Terms.Order.term(true));
private IncludeExclude includeExclude = null;
private String executionHint = null;
private SubAggCollectionMode collectMode = SubAggCollectionMode.DEPTH_FIRST;
private SubAggCollectionMode collectMode = null;
private TermsAggregator.BucketCountThresholds bucketCountThresholds = new TermsAggregator.BucketCountThresholds(
DEFAULT_BUCKET_COUNT_THRESHOLDS);
private boolean showTermDocCountError = false;
@ -71,7 +71,7 @@ public class TermsAggregationBuilder extends ValuesSourceAggregationBuilder<Valu
public TermsAggregationBuilder(StreamInput in) throws IOException {
super(in, StringTerms.TYPE, ValuesSourceType.ANY);
bucketCountThresholds = new BucketCountThresholds(in);
collectMode = SubAggCollectionMode.readFromStream(in);
collectMode = in.readOptionalWriteable(SubAggCollectionMode::readFromStream);
executionHint = in.readOptionalString();
includeExclude = in.readOptionalWriteable(IncludeExclude::new);
order = InternalOrder.Streams.readOrder(in);
@ -86,7 +86,7 @@ public class TermsAggregationBuilder extends ValuesSourceAggregationBuilder<Valu
@Override
protected void innerWriteTo(StreamOutput out) throws IOException {
bucketCountThresholds.writeTo(out);
collectMode.writeTo(out);
out.writeOptionalWriteable(collectMode);
out.writeOptionalString(executionHint);
out.writeOptionalWriteable(includeExclude);
InternalOrder.Streams.writeOrder(order, out);
@ -266,7 +266,9 @@ public class TermsAggregationBuilder extends ValuesSourceAggregationBuilder<Valu
}
builder.field(ORDER_FIELD.getPreferredName());
order.toXContent(builder, params);
builder.field(SubAggCollectionMode.KEY.getPreferredName(), collectMode.parseField().getPreferredName());
if (collectMode != null) {
builder.field(SubAggCollectionMode.KEY.getPreferredName(), collectMode.parseField().getPreferredName());
}
if (includeExclude != null) {
includeExclude.toXContent(builder, params);
}

36
core/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregatorFactory.java
View File

@ -150,6 +150,14 @@ public class TermsAggregatorFactory extends ValuesSourceAggregatorFactory<Values
}
}
}
SubAggCollectionMode cm = collectMode;
if (cm == null) {
cm = SubAggCollectionMode.DEPTH_FIRST;
if (factories != AggregatorFactories.EMPTY) {
cm = subAggCollectionMode(bucketCountThresholds.getShardSize(), maxOrd);
}
}
DocValueFormat format = config.format();
if ((includeExclude != null) && (includeExclude.isRegexBased()) && format != DocValueFormat.RAW) {
throw new AggregationExecutionException("Aggregation [" + name + "] cannot support regular expression style include/exclude "
@ -157,7 +165,7 @@ public class TermsAggregatorFactory extends ValuesSourceAggregatorFactory<Values
}
return execution.create(name, factories, valuesSource, order, format, bucketCountThresholds, includeExclude, context, parent,
collectMode, showTermDocCountError, pipelineAggregators, metaData);
cm, showTermDocCountError, pipelineAggregators, metaData);
}
if ((includeExclude != null) && (includeExclude.isRegexBased())) {
@ -167,19 +175,27 @@ public class TermsAggregatorFactory extends ValuesSourceAggregatorFactory<Values
if (valuesSource instanceof ValuesSource.Numeric) {
IncludeExclude.LongFilter longFilter = null;
SubAggCollectionMode cm = collectMode;
if (cm == null) {
if (factories != AggregatorFactories.EMPTY) {
cm = subAggCollectionMode(bucketCountThresholds.getShardSize(), -1);
} else {
cm = SubAggCollectionMode.DEPTH_FIRST;
}
}
if (((ValuesSource.Numeric) valuesSource).isFloatingPoint()) {
if (includeExclude != null) {
longFilter = includeExclude.convertToDoubleFilter();
}
return new DoubleTermsAggregator(name, factories, (ValuesSource.Numeric) valuesSource, config.format(), order,
bucketCountThresholds, context, parent, collectMode, showTermDocCountError, longFilter,
bucketCountThresholds, context, parent, cm, showTermDocCountError, longFilter,
pipelineAggregators, metaData);
}
if (includeExclude != null) {
longFilter = includeExclude.convertToLongFilter(config.format());
}
return new LongTermsAggregator(name, factories, (ValuesSource.Numeric) valuesSource, config.format(), order,
bucketCountThresholds, context, parent, collectMode, showTermDocCountError, longFilter, pipelineAggregators,
bucketCountThresholds, context, parent, cm, showTermDocCountError, longFilter, pipelineAggregators,
metaData);
}
@ -187,6 +203,20 @@ public class TermsAggregatorFactory extends ValuesSourceAggregatorFactory<Values
+ "]. It can only be applied to numeric or string fields.");
}
// return the SubAggCollectionMode that this aggregation should use based on the expected size
// and the cardinality of the field
static SubAggCollectionMode subAggCollectionMode(int expectedSize, long maxOrd) {
if (expectedSize == Integer.MAX_VALUE) {
// return all buckets
return SubAggCollectionMode.DEPTH_FIRST;
}
if (maxOrd == -1 || maxOrd > expectedSize) {
// use breadth_first if the cardinality is bigger than the expected size or unknown (-1)
return SubAggCollectionMode.BREADTH_FIRST;
}
return SubAggCollectionMode.DEPTH_FIRST;
}
public enum ExecutionMode {
MAP(new ParseField("map")) {

44
core/src/test/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregatorFactoryTests.java Normal file
View File

@ -0,0 +1,44 @@
/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.search.aggregations.bucket.terms;
import org.elasticsearch.search.aggregations.Aggregator;
import org.elasticsearch.test.ESSingleNodeTestCase;
import static org.hamcrest.Matchers.equalTo;
public class TermsAggregatorFactoryTests extends ESSingleNodeTestCase {
public void testSubAggCollectMode() throws Exception {
assertThat(TermsAggregatorFactory.subAggCollectionMode(Integer.MAX_VALUE, -1),
equalTo(Aggregator.SubAggCollectionMode.DEPTH_FIRST));
assertThat(TermsAggregatorFactory.subAggCollectionMode(10, -1),
equalTo(Aggregator.SubAggCollectionMode.BREADTH_FIRST));
assertThat(TermsAggregatorFactory.subAggCollectionMode(10, 5),
equalTo(Aggregator.SubAggCollectionMode.DEPTH_FIRST));
assertThat(TermsAggregatorFactory.subAggCollectionMode(10, 10),
equalTo(Aggregator.SubAggCollectionMode.DEPTH_FIRST));
assertThat(TermsAggregatorFactory.subAggCollectionMode(10, 100),
equalTo(Aggregator.SubAggCollectionMode.BREADTH_FIRST));
assertThat(TermsAggregatorFactory.subAggCollectionMode(1, 2),
equalTo(Aggregator.SubAggCollectionMode.BREADTH_FIRST));
assertThat(TermsAggregatorFactory.subAggCollectionMode(1, 100),
equalTo(Aggregator.SubAggCollectionMode.BREADTH_FIRST));
}
}

18
docs/reference/aggregations/bucket/terms-aggregation.asciidoc
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@ -577,7 +577,8 @@ Deferring calculation of child aggregations
For fields with many unique terms and a small number of required results it can be more efficient to delay the calculation
of child aggregations until the top parent-level aggs have been pruned. Ordinarily, all branches of the aggregation tree
are expanded in one depth-first pass and only then any pruning occurs. In some rare scenarios this can be very wasteful and can hit memory constraints.
are expanded in one depth-first pass and only then any pruning occurs.
In some scenarios this can be very wasteful and can hit memory constraints.
An example problem scenario is querying a movie database for the 10 most popular actors and their 5 most common co-stars:
[source,js]
@ -602,10 +603,13 @@ An example problem scenario is querying a movie database for the 10 most popular
}
--------------------------------------------------
Even though the number of movies may be comparatively small and we want only 50 result buckets there is a combinatorial explosion of buckets
during calculation - a single movie will produce n² buckets where n is the number of actors. The sane option would be to first determine
Even though the number of actors may be comparatively small and we want only 50 result buckets there is a combinatorial explosion of buckets
during calculation - a single actor can produce n² buckets where n is the number of actors. The sane option would be to first determine
the 10 most popular actors and only then examine the top co-stars for these 10 actors. This alternative strategy is what we call the `breadth_first` collection
mode as opposed to the default `depth_first` mode:
mode as opposed to the `depth_first` mode.
NOTE: The `breadth_first` is the default mode for fields with a cardinality bigger than the requested size or when the cardinality is unknown (numeric fields or scripts for instance).
It is possible to override the default heuristic and to provide a collect mode directly in the request:
[source,js]
--------------------------------------------------
@ -615,7 +619,7 @@ mode as opposed to the default `depth_first` mode:
"terms" : {
"field" : "actors",
"size" : 10,
"collect_mode" : "breadth_first"
"collect_mode" : "breadth_first" <1>
},
"aggs" : {
"costars" : {
@ -630,12 +634,10 @@ mode as opposed to the default `depth_first` mode:
}
--------------------------------------------------
<1> the possible values are `breadth_first` and `depth_first`
When using `breadth_first` mode the set of documents that fall into the uppermost buckets are
cached for subsequent replay so there is a memory overhead in doing this which is linear with the number of matching documents.
In most requests the volume of buckets generated is smaller than the number of documents that fall into them so the default `depth_first`
collection mode is normally the best bet but occasionally the `breadth_first` strategy can be significantly more efficient. Currently
elasticsearch will always use the `depth_first` collect_mode unless explicitly instructed to use `breadth_first` as in the above example.
Note that the `order` parameter can still be used to refer to data from a child aggregation when using the `breadth_first` setting - the parent
aggregation understands that this child aggregation will need to be called first before any of the other child aggregations.