Improved warm-up of new segments.

* Merged segments are now warmed-up at the end of the merge operation instead
  of _refresh, so that _refresh doesn't pay the price for the warm-up of merged
  segments, which is often higher than flushed segments because of their size.
* Even when no _warmer is registered, some basic warm-up of the segments is
  performed: norms, doc values (_version). This should help a bit people who
  forget to register warmers.
* Eager loading support for the parent id cache and field data: when one
  can't predict what terms will be present in the index, it is tempting to use
  a match_all query in a warmer, but in that case, query execution might not be
  much faster than field data loading so having a warmer that only loads field
  data without running a query can be useful.

Closes #3819

docs/reference/index-modules/fielddata.asciidoc

@@ -24,6 +24,29 @@ field data after a certain time of inactivity. Defaults to `-1`. For
 example, can be set to `5m` for a 5 minute expiry.
 |=======================================================================
 
+[float]
+=== Fielddata loading
+
+By default, field data is loaded lazily, on the first time that a query that
+requires field data is fired. However, this can make the first requests that
+follow a merge operation quite slow since fielddata loading is a heavy
+operation.
+
+It is possible to force field data to be loaded and cached eagerly through the
+`loading` setting of fielddata:
+
+[source,js]
+--------------------------------------------------
+{
+    category: {
+        type:      "string",
+        fielddata: {
+            loading: "eager"
+        }
+    }
+}
+--------------------------------------------------
+
 [float]
 [[field-data-filtering]]
 === Filtering fielddata

src/main/java/org/elasticsearch/index/engine/robin/RobinEngine.java

@@ -21,6 +21,7 @@ package org.elasticsearch.index.engine.robin;
 
 import com.google.common.collect.Lists;
 import org.apache.lucene.index.*;
+import org.apache.lucene.index.IndexWriter.IndexReaderWarmer;
 import org.apache.lucene.search.IndexSearcher;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.SearcherFactory;
@@ -1283,6 +1284,15 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine {
         }
     }
 
+    /** Returns whether a leaf reader comes from a merge (versus flush or addIndexes). */
+    private static boolean isMergedSegment(AtomicReader reader) {
+        // We expect leaves to be segment readers
+        final Map<String, String> diagnostics = ((SegmentReader) reader).getSegmentInfo().info.getDiagnostics();
+        final String source = diagnostics.get(IndexWriter.SOURCE);
+        assert Arrays.asList(IndexWriter.SOURCE_ADDINDEXES_READERS, IndexWriter.SOURCE_FLUSH, IndexWriter.SOURCE_MERGE).contains(source) : "Unknown source " + source;
+        return IndexWriter.SOURCE_MERGE.equals(source);
+    }
+
     private IndexWriter createWriter() throws IOException {
         try {
             // release locks when started
@@ -1313,6 +1323,28 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine {
              * in combination with the default writelock timeout*/
             config.setWriteLockTimeout(5000);
             config.setUseCompoundFile(this.compoundOnFlush);
+            // Warm-up hook for newly-merged segments. Warming up segments here is better since it will be performed at the end
+            // of the merge operation and won't slow down _refresh
+            config.setMergedSegmentWarmer(new IndexReaderWarmer() {
+                @Override
+                public void warm(AtomicReader reader) throws IOException {
+                    try {
+                        assert isMergedSegment(reader);
+                        final Engine.Searcher searcher = new SimpleSearcher("warmer", new IndexSearcher(reader));
+                        final IndicesWarmer.WarmerContext context = new IndicesWarmer.WarmerContext(shardId, searcher);
+                        warmer.warm(context);
+                    } catch (Throwable t) {
+                        // Don't fail a merge if the warm-up failed
+                        if (!closed) {
+                            logger.warn("Warm-up failed", t);
+                        }
+                        if (t instanceof Error) {
+                            // assertion/out-of-memory error, don't ignore those
+                            throw (Error) t;
+                        }
+                    }
+                }
+            });
             return new IndexWriter(store.directory(), config);
         } catch (LockObtainFailedException ex) {
             boolean isLocked = IndexWriter.isLocked(store.directory());
@@ -1485,6 +1517,10 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine {
                         // figure out the newSearcher, with only the new readers that are relevant for us
                         List<IndexReader> readers = Lists.newArrayList();
                         for (AtomicReaderContext newReaderContext : searcher.getIndexReader().leaves()) {
+                            if (isMergedSegment(newReaderContext.reader())) {
+                                // merged segments are already handled by IndexWriterConfig.setMergedSegmentWarmer
+                                continue;
+                            }
                             boolean found = false;
                             for (AtomicReaderContext currentReaderContext : currentSearcher.reader().leaves()) {
                                 if (currentReaderContext.reader().getCoreCacheKey().equals(newReaderContext.reader().getCoreCacheKey())) {
@@ -1505,7 +1541,6 @@ public class RobinEngine extends AbstractIndexShardComponent implements Engine {
 
                     if (newSearcher != null) {
                         IndicesWarmer.WarmerContext context = new IndicesWarmer.WarmerContext(shardId,
-                                new SimpleSearcher("warmer", searcher),
                                 new SimpleSearcher("warmer", newSearcher));
                         warmer.warm(context);
                     }

src/main/java/org/elasticsearch/index/fielddata/FieldDataType.java

@@ -21,12 +21,22 @@ package org.elasticsearch.index.fielddata;
 
 import org.elasticsearch.common.settings.ImmutableSettings;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.index.mapper.MapperParsingException;
 
 /**
  */
 public class FieldDataType {
 
+    private static final String LOADING_KEY = "loading";
+    private static final String EAGER_LOADING_VALUE = "eager";
+    private static final String LAZY_LOADING_VALUE = "lazy";
+
+    public static enum Loading {
+        LAZY, EAGER;
+    }
+
     private final String type;
+    private final Loading loading;
     private final Settings settings;
 
     public FieldDataType(String type) {
@@ -40,6 +50,14 @@ public class FieldDataType {
     public FieldDataType(String type, Settings settings) {
         this.type = type;
         this.settings = settings;
+        final String loading = settings.get(LOADING_KEY);
+        if (loading == null || loading.equals(LAZY_LOADING_VALUE)) {
+            this.loading = Loading.LAZY;
+        } else if (loading.equals(EAGER_LOADING_VALUE)) {
+            this.loading = Loading.EAGER;
+        } else {
+            throw new MapperParsingException("Unknown [" + LOADING_KEY + "] value: [" + loading + "]");
+        }
     }
 
     public String getType() {
@@ -50,6 +68,10 @@ public class FieldDataType {
         return this.settings;
     }
 
+    public Loading getLoading() {
+        return loading;
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

src/main/java/org/elasticsearch/index/shard/service/IndexShard.java

@@ -30,12 +30,14 @@ import org.elasticsearch.index.cache.id.ShardIdCache;
 import org.elasticsearch.index.engine.Engine;
 import org.elasticsearch.index.engine.EngineException;
 import org.elasticsearch.index.fielddata.FieldDataStats;
+import org.elasticsearch.index.fielddata.IndexFieldDataService;
 import org.elasticsearch.index.fielddata.ShardFieldData;
 import org.elasticsearch.index.flush.FlushStats;
 import org.elasticsearch.index.get.GetStats;
 import org.elasticsearch.index.get.ShardGetService;
 import org.elasticsearch.index.indexing.IndexingStats;
 import org.elasticsearch.index.indexing.ShardIndexingService;
+import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.mapper.ParsedDocument;
 import org.elasticsearch.index.mapper.SourceToParse;
 import org.elasticsearch.index.merge.MergeStats;
@@ -44,6 +46,7 @@ import org.elasticsearch.index.percolator.stats.ShardPercolateService;
 import org.elasticsearch.index.refresh.RefreshStats;
 import org.elasticsearch.index.search.stats.SearchStats;
 import org.elasticsearch.index.search.stats.ShardSearchService;
+import org.elasticsearch.index.service.IndexService;
 import org.elasticsearch.index.shard.DocsStats;
 import org.elasticsearch.index.shard.IndexShardComponent;
 import org.elasticsearch.index.shard.IndexShardState;
@@ -106,6 +109,12 @@ public interface IndexShard extends IndexShardComponent {
 
     ShardTermVectorService termVectorService();
 
+    MapperService mapperService();
+
+    IndexFieldDataService indexFieldDataService();
+
+    IndexService indexService();
+
     IndexShardState state();
 
     Engine.Create prepareCreate(SourceToParse source) throws ElasticSearchException;

src/main/java/org/elasticsearch/index/shard/service/InternalIndexShard.java

@@ -50,6 +50,7 @@ import org.elasticsearch.index.cache.id.ShardIdCache;
 import org.elasticsearch.index.codec.CodecService;
 import org.elasticsearch.index.engine.*;
 import org.elasticsearch.index.fielddata.FieldDataStats;
+import org.elasticsearch.index.fielddata.IndexFieldDataService;
 import org.elasticsearch.index.fielddata.ShardFieldData;
 import org.elasticsearch.index.flush.FlushStats;
 import org.elasticsearch.index.get.GetStats;
@@ -66,6 +67,7 @@ import org.elasticsearch.index.refresh.RefreshStats;
 import org.elasticsearch.index.search.nested.NonNestedDocsFilter;
 import org.elasticsearch.index.search.stats.SearchStats;
 import org.elasticsearch.index.search.stats.ShardSearchService;
+import org.elasticsearch.index.service.IndexService;
 import org.elasticsearch.index.settings.IndexSettings;
 import org.elasticsearch.index.settings.IndexSettingsService;
 import org.elasticsearch.index.shard.*;
@@ -116,6 +118,8 @@ public class InternalIndexShard extends AbstractIndexShardComponent implements I
     private final ShardPercolateService shardPercolateService;
     private final CodecService codecService;
     private final ShardTermVectorService termVectorService;
+    private final IndexFieldDataService indexFieldDataService;
+    private final IndexService indexService;
 
     private final Object mutex = new Object();
     private final String checkIndexOnStartup;
@@ -141,7 +145,7 @@ public class InternalIndexShard extends AbstractIndexShardComponent implements I
                               ThreadPool threadPool, MapperService mapperService, IndexQueryParserService queryParserService, IndexCache indexCache, IndexAliasesService indexAliasesService, ShardIndexingService indexingService, ShardGetService getService, ShardSearchService searchService, ShardIndexWarmerService shardWarmerService,
                               ShardFilterCache shardFilterCache, ShardIdCache shardIdCache, ShardFieldData shardFieldData,
                               PercolatorQueriesRegistry percolatorQueriesRegistry, ShardPercolateService shardPercolateService, CodecService codecService,
-                              ShardTermVectorService termVectorService) {
+                              ShardTermVectorService termVectorService, IndexFieldDataService indexFieldDataService, IndexService indexService) {
         super(shardId, indexSettings);
         this.indicesLifecycle = (InternalIndicesLifecycle) indicesLifecycle;
         this.indexSettingsService = indexSettingsService;
@@ -164,6 +168,8 @@ public class InternalIndexShard extends AbstractIndexShardComponent implements I
         this.shardFieldData = shardFieldData;
         this.percolatorQueriesRegistry = percolatorQueriesRegistry;
         this.shardPercolateService = shardPercolateService;
+        this.indexFieldDataService = indexFieldDataService;
+        this.indexService = indexService;
         this.codecService = codecService;
         state = IndexShardState.CREATED;
 
@@ -207,6 +213,20 @@ public class InternalIndexShard extends AbstractIndexShardComponent implements I
         return termVectorService;
     }
 
+    @Override
+    public IndexFieldDataService indexFieldDataService() {
+        return indexFieldDataService;
+    }
+
+    @Override
+    public MapperService mapperService() {
+        return mapperService;
+    }
+
+    @Override
+    public IndexService indexService() {
+        return indexService;
+    }
 
     @Override
     public ShardSearchService searchService() {

src/main/java/org/elasticsearch/indices/warmer/IndicesWarmer.java

@@ -35,19 +35,17 @@ public interface IndicesWarmer {
             return ThreadPool.Names.WARMER;
         }
 
-        public abstract void warm(IndexShard indexShard, IndexMetaData indexMetaData, WarmerContext context);
+        public abstract void warm(IndexShard indexShard, IndexMetaData indexMetaData, WarmerContext context, ThreadPool threadPool);
     }
 
     public static class WarmerContext {
 
         private final ShardId shardId;
 
-        private final Engine.Searcher fullSearcher;
         private final Engine.Searcher newSearcher;
 
-        public WarmerContext(ShardId shardId, Engine.Searcher fullSearcher, Engine.Searcher newSearcher) {
+        public WarmerContext(ShardId shardId, Engine.Searcher newSearcher) {
             this.shardId = shardId;
-            this.fullSearcher = fullSearcher;
             this.newSearcher = newSearcher;
         }
 
@@ -55,10 +53,7 @@ public interface IndicesWarmer {
             return shardId;
         }
 
-        public Engine.Searcher fullSearcher() {
+        /** Return a searcher instance that only wraps the segments to warm. */
-            return fullSearcher;
-        }
-
         public Engine.Searcher newSearcher() {
             return newSearcher;
         }

src/main/java/org/elasticsearch/indices/warmer/InternalIndicesWarmer.java

@@ -31,7 +31,6 @@ import org.elasticsearch.indices.IndicesService;
 import org.elasticsearch.threadpool.ThreadPool;
 
 import java.util.concurrent.CopyOnWriteArrayList;
-import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -83,29 +82,12 @@ public class InternalIndicesWarmer extends AbstractComponent implements IndicesW
             return;
         }
         if (logger.isTraceEnabled()) {
-            logger.trace("[{}][{}] warming [{}], new [{}]", context.shardId().index().name(), context.shardId().id(), context.fullSearcher().reader(), context.newSearcher().reader());
+            logger.trace("[{}][{}] warming [{}]", context.shardId().index().name(), context.shardId().id(), context.newSearcher().reader());
         }
         indexShard.warmerService().onPreWarm();
         long time = System.nanoTime();
         for (final Listener listener : listeners) {
-            final CountDownLatch latch = new CountDownLatch(1);
+            listener.warm(indexShard, indexMetaData, context, threadPool);
-            threadPool.executor(listener.executor()).execute(new Runnable() {
-                @Override
-                public void run() {
-                    try {
-                        listener.warm(indexShard, indexMetaData, context);
-                    } catch (Throwable e) {
-                        indexShard.warmerService().logger().warn("failed to warm [{}]", e, listener);
-                    } finally {
-                        latch.countDown();
-                    }
-                }
-            });
-            try {
-                latch.await();
-            } catch (InterruptedException e) {
-                return;
-            }
         }
         long took = System.nanoTime() - time;
         indexShard.warmerService().onPostWarm(took);

src/main/java/org/elasticsearch/search/SearchService.java

@@ -20,8 +20,12 @@
 package org.elasticsearch.search;
 
 import com.google.common.collect.ImmutableMap;
+import org.apache.lucene.index.AtomicReaderContext;
+import org.apache.lucene.index.SimpleMergedSegmentWarmer;
 import org.apache.lucene.search.TopDocs;
+import org.apache.lucene.util.InfoStream;
 import org.elasticsearch.ElasticSearchException;
+import org.elasticsearch.ElasticSearchIllegalStateException;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.action.search.SearchType;
 import org.elasticsearch.cache.recycler.CacheRecycler;
@@ -39,12 +43,19 @@ import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.index.engine.Engine;
+import org.elasticsearch.index.fielddata.FieldDataType;
+import org.elasticsearch.index.fielddata.IndexFieldDataService;
+import org.elasticsearch.index.mapper.DocumentMapper;
+import org.elasticsearch.index.mapper.FieldMapper;
+import org.elasticsearch.index.mapper.MapperService;
+import org.elasticsearch.index.mapper.internal.ParentFieldMapper;
 import org.elasticsearch.index.search.stats.StatsGroupsParseElement;
 import org.elasticsearch.index.service.IndexService;
 import org.elasticsearch.index.shard.service.IndexShard;
 import org.elasticsearch.indices.IndicesLifecycle;
 import org.elasticsearch.indices.IndicesService;
 import org.elasticsearch.indices.warmer.IndicesWarmer;
+import org.elasticsearch.indices.warmer.IndicesWarmer.WarmerContext;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.dfs.CachedDfSource;
 import org.elasticsearch.search.dfs.DfsPhase;
@@ -60,6 +71,7 @@ import org.elasticsearch.threadpool.ThreadPool;
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.atomic.AtomicLong;
 
@@ -125,6 +137,8 @@ public class SearchService extends AbstractLifecycleComponent<SearchService> {
 
         this.keepAliveReaper = threadPool.scheduleWithFixedDelay(new Reaper(), keepAliveInterval);
 
+        this.indicesWarmer.addListener(new IndexReaderWarmer());
+        this.indicesWarmer.addListener(new FieldDataWarmer());
         this.indicesWarmer.addListener(new SearchWarmer());
     }
 
@@ -618,15 +632,123 @@ public class SearchService extends AbstractLifecycleComponent<SearchService> {
         }
     }
 
+    static class IndexReaderWarmer extends IndicesWarmer.Listener {
+
+        private final SimpleMergedSegmentWarmer warmer = new SimpleMergedSegmentWarmer(InfoStream.NO_OUTPUT);
+
+        @Override
+        public void warm(IndexShard indexShard, IndexMetaData indexMetaData, WarmerContext context, ThreadPool threadPool) {
+            long start = System.nanoTime();
+            try {
+                for (AtomicReaderContext ctx : context.newSearcher().reader().leaves()) {
+                    warmer.warm(ctx.reader());
+                }
+                if (indexShard.warmerService().logger().isTraceEnabled()) {
+                    indexShard.warmerService().logger().trace("warmed readers, took [{}]", TimeValue.timeValueNanos(System.nanoTime() - start));
+                }
+            } catch (Throwable t) {
+                throw new ElasticSearchIllegalStateException("Unexpected exception while warming-up segment", t);
+            }
+        }
+
+    }
+
+    static class FieldDataWarmer extends IndicesWarmer.Listener {
+
+        @Override
+        public void warm(final IndexShard indexShard, IndexMetaData indexMetaData, final WarmerContext context, ThreadPool threadPool) {
+            final MapperService mapperService = indexShard.mapperService();
+            final Map<String, FieldMapper<?>> warmUp = new HashMap<String, FieldMapper<?>>();
+            boolean parentChild = false;
+            for (DocumentMapper docMapper : mapperService) {
+                for (FieldMapper<?> fieldMapper : docMapper.mappers().mappers()) {
+                    if (fieldMapper instanceof ParentFieldMapper) {
+                        parentChild = true;
+                    }
+                    final FieldDataType fieldDataType = fieldMapper.fieldDataType();
+                    if (fieldDataType == null) {
+                        continue;
+                    }
+                    if (fieldDataType.getLoading() != FieldDataType.Loading.EAGER) {
+                        continue;
+                    }
+                    final String indexName = fieldMapper.names().indexName();
+                    if (warmUp.containsKey(indexName)) {
+                        continue;
+                    }
+                    warmUp.put(indexName, fieldMapper);
+                }
+            }
+            final IndexFieldDataService indexFieldDataService = indexShard.indexFieldDataService();
+            final int numTasks = warmUp.size() * context.newSearcher().reader().leaves().size() + (parentChild ? 1 : 0);
+            final CountDownLatch latch = new CountDownLatch(numTasks);
+            for (final AtomicReaderContext ctx : context.newSearcher().reader().leaves()) {
+                for (final FieldMapper<?> fieldMapper : warmUp.values()) {
+                    threadPool.executor(executor()).execute(new Runnable() {
+
+                        @Override
+                        public void run() {
+                            try {
+                                final long start = System.nanoTime();
+                                indexFieldDataService.getForField(fieldMapper).load(ctx);
+                                if (indexShard.warmerService().logger().isTraceEnabled()) {
+                                    indexShard.warmerService().logger().trace("warmed fielddata for [{}], took [{}]", fieldMapper.names().name(), TimeValue.timeValueNanos(System.nanoTime() - start));
+                                }
+                            } catch (Throwable t) {
+                                indexShard.warmerService().logger().warn("failed to warm-up fielddata for [{}]", t, fieldMapper.names().name());
+                            } finally {
+                                latch.countDown();
+                            }
+                        }
+
+                    });
+                }
+            }
+
+            if (parentChild) {
+                threadPool.executor(executor()).execute(new Runnable() {
+
+                    @Override
+                    public void run() {
+                        try {
+                            final long start = System.nanoTime();
+                            indexShard.indexService().cache().idCache().refresh(context.newSearcher().reader().leaves());
+                            if (indexShard.warmerService().logger().isTraceEnabled()) {
+                                indexShard.warmerService().logger().trace("warmed id_cache, took [{}]", TimeValue.timeValueNanos(System.nanoTime() - start));
+                            }
+                        } catch (Throwable t) {
+                            indexShard.warmerService().logger().warn("failed to warm-up id cache", t);
+                        } finally {
+                            latch.countDown();
+                        }
+                    }
+
+                });
+            }
+
+            try {
+                latch.await();
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+        }
+
+    }
+
     class SearchWarmer extends IndicesWarmer.Listener {
 
         @Override
-        public void warm(IndexShard indexShard, IndexMetaData indexMetaData, IndicesWarmer.WarmerContext warmerContext) {
+        public void warm(final IndexShard indexShard, final IndexMetaData indexMetaData, final IndicesWarmer.WarmerContext warmerContext, ThreadPool threadPool) {
             IndexWarmersMetaData custom = indexMetaData.custom(IndexWarmersMetaData.TYPE);
             if (custom == null) {
                 return;
             }
-            for (IndexWarmersMetaData.Entry entry : custom.entries()) {
+            final CountDownLatch latch = new CountDownLatch(custom.entries().size());
+            for (final IndexWarmersMetaData.Entry entry : custom.entries()) {
+                threadPool.executor(executor()).execute(new Runnable() {
+
+                    @Override
+                    public void run() {
                         SearchContext context = null;
                         try {
                             long now = System.nanoTime();
@@ -643,13 +765,26 @@ public class SearchService extends AbstractLifecycleComponent<SearchService> {
                         } catch (Throwable t) {
                             indexShard.warmerService().logger().warn("warmer [{}] failed", t, entry.name());
                         } finally {
+                            try {
                                 if (context != null) {
                                     freeContext(context);
                                     cleanContext(context);
                                 }
+                            } finally {
+                                latch.countDown();
                             }
                         }
                     }
+
+                });
+            }
+
+            try {
+                latch.await();
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+        }
     }
 
     class Reaper implements Runnable {

src/test/java/org/elasticsearch/search/child/SimpleChildQuerySearchTests.java

@@ -345,12 +345,22 @@ public class SimpleChildQuerySearchTests extends AbstractIntegrationTest {
                                 .put("index.number_of_replicas", 0)
                 ).execute().actionGet();
         client().admin().cluster().prepareHealth().setWaitForEvents(Priority.LANGUID).setWaitForGreenStatus().execute().actionGet();
+
+        client().prepareIndex("test", "parent", "p0").setSource("p_field", "p_value0").execute().actionGet();
+        client().prepareIndex("test", "parent", "p1").setSource("p_field", "p_value1").execute().actionGet();
+
+        client().admin().indices().prepareRefresh().execute().actionGet();
+        // No _parent field yet, there shouldn't be anything in the parent id cache
+        IndicesStatsResponse indicesStatsResponse = client().admin().indices()
+                .prepareStats("test").setIdCache(true).execute().actionGet();
+        assertThat(indicesStatsResponse.getTotal().getIdCache().getMemorySizeInBytes(), equalTo(0l));
+
+        // Now add mapping + children
         client().admin().indices().preparePutMapping("test").setType("child").setSource(jsonBuilder().startObject().startObject("type")
                 .startObject("_parent").field("type", "parent").endObject()
                 .endObject().endObject()).execute().actionGet();
 
         // index simple data
-        client().prepareIndex("test", "parent", "p1").setSource("p_field", "p_value1").execute().actionGet();
         client().prepareIndex("test", "child", "c1").setSource("c_field", "red").setParent("p1").execute().actionGet();
         client().prepareIndex("test", "child", "c2").setSource("c_field", "yellow").setParent("p1").execute().actionGet();
         client().prepareIndex("test", "parent", "p2").setSource("p_field", "p_value2").execute().actionGet();
@@ -359,9 +369,10 @@ public class SimpleChildQuerySearchTests extends AbstractIntegrationTest {
 
         client().admin().indices().prepareRefresh().execute().actionGet();
 
-        IndicesStatsResponse indicesStatsResponse = client().admin().indices()
+        indicesStatsResponse = client().admin().indices()
                 .prepareStats("test").setIdCache(true).execute().actionGet();
-        assertThat(indicesStatsResponse.getTotal().getIdCache().getMemorySizeInBytes(), equalTo(0l));
+        // automatic warm-up has populated the cache since it found a parent field mapper
+        assertThat(indicesStatsResponse.getTotal().getIdCache().getMemorySizeInBytes(), greaterThan(0l));
 
         SearchResponse searchResponse = client().prepareSearch("test")
                 .setQuery(constantScoreQuery(hasChildFilter("child", termQuery("c_field", "blue"))))

src/test/java/org/elasticsearch/search/facet/ExtendedFacetsTests.java

@@ -52,6 +52,7 @@ public class ExtendedFacetsTests extends AbstractIntegrationTest {
                         .field("index", "not_analyzed")
                         .startObject("fielddata")
                         .field("format", "paged_bytes")
+                        .field("loading", randomBoolean() ? "eager" : "lazy")
                         .endObject()
                         .endObject()
                         .startObject("field1_fst")
@@ -59,6 +60,7 @@ public class ExtendedFacetsTests extends AbstractIntegrationTest {
                         .field("index", "not_analyzed")
                         .startObject("fielddata")
                         .field("format", "fst")
+                        .field("loading", randomBoolean() ? "eager" : "lazy")
                         .endObject()
                         .endObject()
                         .startObject("field2")
@@ -66,6 +68,7 @@ public class ExtendedFacetsTests extends AbstractIntegrationTest {
                         .field("index", "not_analyzed")
                         .startObject("fielddata")
                         .field("format", "fst")
+                        .field("loading", randomBoolean() ? "eager" : "lazy")
                         .endObject()
                         .endObject()
                         .startObject("q_field")

src/test/java/org/elasticsearch/search/facet/SimpleFacetsTests.java

@@ -485,30 +485,30 @@ public class SimpleFacetsTests extends AbstractIntegrationTest {
                 .addMapping("type", jsonBuilder().startObject().startObject("type").startObject("properties")
                         .startObject("name_paged")
                         .field("type", "string")
-                        .startObject("fielddata").field("format", "paged_bytes").endObject()
+                        .startObject("fielddata").field("format", "paged_bytes").field("loading", randomBoolean() ? "eager" : "lazy").endObject()
                         .endObject()
                         .startObject("name_fst")
                         .field("type", "string")
-                        .startObject("fielddata").field("format", "fst").endObject()
+                        .startObject("fielddata").field("format", "fst").field("loading", randomBoolean() ? "eager" : "lazy").endObject()
                         .endObject()
                         .startObject("name_paged_mv")
                         .field("type", "string")
-                        .startObject("fielddata").field("format", "paged_bytes").endObject()
+                        .startObject("fielddata").field("format", "paged_bytes").field("loading", randomBoolean() ? "eager" : "lazy").endObject()
                         .endObject()
                         .startObject("name_fst_mv")
                         .field("type", "string")
-                        .startObject("fielddata").field("format", "fst").endObject()
+                        .startObject("fielddata").field("format", "fst").field("loading", randomBoolean() ? "eager" : "lazy").endObject()
                         .endObject()
                         .startObject("filtered")
                         .field("type", "string")
-                        .startObject("fielddata").field("format", "fst").startObject("filter")
+                        .startObject("fielddata").field("format", "fst").field("loading", randomBoolean() ? "eager" : "lazy").startObject("filter")
                         .startObject("regex").field("pattern", "\\d{1,2}").endObject().endObject()
                         .endObject()
                                 // only 1 or 2 digits
                         .endObject()
                         .startObject("filtered_mv")
                         .field("type", "string")
-                        .startObject("fielddata").field("format", "fst").startObject("filter")
+                        .startObject("fielddata").field("format", "fst").field("loading", randomBoolean() ? "eager" : "lazy").startObject("filter")
                         .startObject("regex").field("pattern", "\\d{1,2}").endObject().endObject()
                         .endObject()
                         .endObject().endObject().endObject())