QueryEngine result cache (#1279)

* Add QueryEngine cache API

* Remove outdated javadoc text

elide-datastore/elide-datastore-aggregation/src/main/java/com/yahoo/elide/datastores/aggregation/AggregationDataStoreTransaction.java

@@ -53,7 +53,7 @@ public void createObject(Object entity, RequestScope scope) {
     @Override
     public Iterable<Object> loadObjects(EntityProjection entityProjection, RequestScope scope) {
         Query query = buildQuery(entityProjection, scope);
-        return queryEngine.executeQuery(query);
+        return queryEngine.executeQuery(query, true);
     }
 
     @Override

elide-datastore/elide-datastore-aggregation/src/main/java/com/yahoo/elide/datastores/aggregation/QueryEngine.java

@@ -14,6 +14,7 @@
 import com.yahoo.elide.datastores.aggregation.metadata.models.Metric;
 import com.yahoo.elide.datastores.aggregation.metadata.models.Table;
 import com.yahoo.elide.datastores.aggregation.metadata.models.TimeDimension;
+import com.yahoo.elide.datastores.aggregation.query.Cache;
 import com.yahoo.elide.datastores.aggregation.query.ColumnProjection;
 import com.yahoo.elide.datastores.aggregation.query.MetricProjection;
 import com.yahoo.elide.datastores.aggregation.query.Query;
@@ -65,8 +66,6 @@
  * </pre>
  * Implementor must assume that {@link DataStoreTransaction} will never keep reference to any internal state of a
  * {@link QueryEngine} object. This ensures the plugability of various {@link QueryEngine} implementations.
- * <p>
- * This is a {@link java.util.function functional interface} whose functional method is {@link #executeQuery(Query)}.
  */
 public abstract class QueryEngine {
     @Getter
@@ -77,18 +76,26 @@ public abstract class QueryEngine {
 
     private final Map<String, Table> tables;
 
+    protected final Cache cache;
+
     /**
      * QueryEngine is constructed with a metadata store and is responsible for constructing all Tables and Entities
      * metadata in this metadata store.
      *
      * @param metaDataStore a metadata store
+     * @param cache the cache for query results, or null
      */
-    public QueryEngine(MetaDataStore metaDataStore) {
+    public QueryEngine(MetaDataStore metaDataStore, Cache cache) {
         this.metaDataStore = metaDataStore;
         this.metadataDictionary = metaDataStore.getDictionary();
         populateMetaData(metaDataStore);
         this.tables = metaDataStore.getMetaData(Table.class).stream()
                 .collect(Collectors.toMap(Table::getId, Functions.identity()));
+        if (cache != null) {
+            this.cache = cache;
+        } else {
+            this.cache = new NoCache();
+        }
     }
 
     /**
@@ -154,13 +161,13 @@ private void populateMetaData(MetaDataStore metaDataStore) {
 
     /**
      * Executes the specified {@link Query} against a specific persistent storage, which understand the provided
-     * {@link Query}.
-     *
-     * @param query  The query customized for a particular persistent storage or storage client
+     * {@link Query}. Results may be taken from a cache, if configured.
      *
+     * @param query    The query customized for a particular persistent storage or storage client
+     * @param useCache Whether to use the cache, if configured
      * @return query results
      */
-    public abstract Iterable<Object> executeQuery(Query query);
+    public abstract Iterable<Object> executeQuery(Query query, boolean useCache);
 
     /**
      * Returns the schema for a given entity class.
@@ -170,4 +177,16 @@ private void populateMetaData(MetaDataStore metaDataStore) {
     public Table getTable(String classAlias) {
         return tables.get(classAlias);
     }
+
+    private static class NoCache implements Cache {
+        @Override
+        public Iterable<Object> get(Object key) {
+            return null;
+        }
+
+        @Override
+        public void put(Object key, Iterable<Object> result) {
+            // Do nothing
+        }
+    }
 }

elide-datastore/elide-datastore-aggregation/src/main/java/com/yahoo/elide/datastores/aggregation/query/Cache.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2020, Yahoo Inc.
+ * Licensed under the Apache License, Version 2.0
+ * See LICENSE file in project root for terms.
+ */
+package com.yahoo.elide.datastores.aggregation.query;
+
+/**
+ * A cache for Query results.
+ */
+public interface Cache {
+    /**
+     * Load Query result from cache. Exceptions should be passed through.
+     *
+     * @param key    a key to look up in the cache.
+     * @return query results from cache, or null if not found.
+     */
+    Iterable<Object> get(Object key);
+
+    /**
+     * Insert results into cache.
+     *
+     * @param key    the key to associate with the query
+     * @param result the result to cache with the key
+     */
+    void put(Object key, Iterable<Object> result);
+}

elide-datastore/elide-datastore-aggregation/src/main/java/com/yahoo/elide/datastores/aggregation/queryengines/AbstractEntityHydrator.java

@@ -27,7 +27,7 @@
 import java.util.stream.Collectors;
 
 /**
- * {@link AbstractEntityHydrator} hydrates the entity loaded by {@link QueryEngine#executeQuery(Query)}.
+ * {@link AbstractEntityHydrator} hydrates the entity loaded by {@link QueryEngine#executeQuery(Query, boolean)}.
  * <p>
  * {@link AbstractEntityHydrator} is not thread-safe and should be accessed by only 1 thread in this application,
  * because it uses {@link StitchList}. See {@link StitchList} for more details.
@@ -49,8 +49,8 @@ public abstract class AbstractEntityHydrator {
     /**
      * Constructor.
      *
-     * @param results The loaded objects from {@link QueryEngine#executeQuery(Query)}
-     * @param query  The query passed to {@link QueryEngine#executeQuery(Query)} to load the objects
+     * @param results The loaded objects from {@link QueryEngine#executeQuery(Query, boolean)}
+     * @param query  The query passed to {@link QueryEngine#executeQuery(Query, boolean)} to load the objects
      * @param entityDictionary  An object that sets entity instance values and provides entity metadata info
      */
     public AbstractEntityHydrator(List<Object> results, Query query, EntityDictionary entityDictionary) {

elide-datastore/elide-datastore-aggregation/src/main/java/com/yahoo/elide/datastores/aggregation/queryengines/sql/SQLEntityHydrator.java

@@ -22,7 +22,7 @@
 import javax.persistence.EntityManager;
 
 /**
- * {@link SQLEntityHydrator} hydrates the entity loaded by {@link SQLQueryEngine#executeQuery(Query)}.
+ * {@link SQLEntityHydrator} hydrates the entity loaded by {@link SQLQueryEngine#executeQuery(Query, boolean)}.
  */
 public class SQLEntityHydrator extends AbstractEntityHydrator {
 
@@ -32,8 +32,8 @@ public class SQLEntityHydrator extends AbstractEntityHydrator {
     /**
      * Constructor.
      *
-     * @param results The loaded objects from {@link SQLQueryEngine#executeQuery(Query)}
-     * @param query  The query passed to {@link SQLQueryEngine#executeQuery(Query)} to load the objects
+     * @param results The loaded objects from {@link SQLQueryEngine#executeQuery(Query, boolean)}
+     * @param query  The query passed to {@link SQLQueryEngine#executeQuery(Query, boolean)} to load the objects
      * @param entityDictionary  An object that sets entity instance values and provides entity metadata info
      * @param entityManager  An service that issues JPQL queries to load relationship objects
      */

elide-datastore/elide-datastore-aggregation/src/main/java/com/yahoo/elide/datastores/aggregation/queryengines/sql/SQLQueryEngine.java

@@ -19,6 +19,7 @@
 import com.yahoo.elide.datastores.aggregation.metadata.models.Metric;
 import com.yahoo.elide.datastores.aggregation.metadata.models.Table;
 import com.yahoo.elide.datastores.aggregation.metadata.models.TimeDimension;
+import com.yahoo.elide.datastores.aggregation.query.Cache;
 import com.yahoo.elide.datastores.aggregation.query.ColumnProjection;
 import com.yahoo.elide.datastores.aggregation.query.MetricProjection;
 import com.yahoo.elide.datastores.aggregation.query.Query;
@@ -61,8 +62,8 @@ public class SQLQueryEngine extends QueryEngine {
 
     private final SQLReferenceTable referenceTable;
 
-    public SQLQueryEngine(MetaDataStore metaDataStore, EntityManagerFactory entityManagerFactory) {
-        super(metaDataStore);
+    public SQLQueryEngine(MetaDataStore metaDataStore, EntityManagerFactory entityManagerFactory, Cache cache) {
+        super(metaDataStore, cache);
         this.entityManagerFactory = entityManagerFactory;
         this.referenceTable = new SQLReferenceTable(metaDataStore);
     }
@@ -114,7 +115,7 @@ public MetricProjection constructMetricProjection(Metric metric,
     }
 
     @Override
-    public Iterable<Object> executeQuery(Query query) {
+    public Iterable<Object> executeQuery(Query query, boolean useCache) {
         EntityManager entityManager = null;
         EntityTransaction transaction = null;
         try {

elide-datastore/elide-datastore-aggregation/src/test/java/com/yahoo/elide/datastores/aggregation/annotation/dimensionformula/DimensionFormulaTest.java

@@ -24,7 +24,7 @@ public void testReferenceLoop() {
 
         IllegalArgumentException exception = assertThrows(
                 IllegalArgumentException.class,
-                () -> new SQLQueryEngine(metaDataStore, null));
+                () -> new SQLQueryEngine(metaDataStore, null, null));
         assertEquals(
                 "Formula reference loop found: loop.playerLevel->loop.playerLevel",
                 exception.getMessage());
@@ -36,7 +36,7 @@ public void testJoinToLoop() {
 
         IllegalArgumentException exception = assertThrows(
                 IllegalArgumentException.class,
-                () -> new SQLQueryEngine(metaDataStore, null));
+                () -> new SQLQueryEngine(metaDataStore, null, null));
         assertEquals(
                 "Formula reference loop found: joinToLoop.playerLevel->joinToLoop.playerLevel",
                 exception.getMessage());
@@ -49,7 +49,7 @@ public void testCrossClassReferenceLoop() {
 
         IllegalArgumentException exception = assertThrows(
                 IllegalArgumentException.class,
-                () -> new SQLQueryEngine(metaDataStore, null));
+                () -> new SQLQueryEngine(metaDataStore, null, null));
 
         String exception1 = "Formula reference loop found: loopCountryA.inUsa->loopCountryB.inUsa->loopCountryA.inUsa";
 

elide-datastore/elide-datastore-aggregation/src/test/java/com/yahoo/elide/datastores/aggregation/annotation/metricformula/MetricFormulaTest.java

@@ -21,7 +21,7 @@ public void testReferenceLoop() {
 
         IllegalArgumentException exception = assertThrows(
                 IllegalArgumentException.class,
-                () -> new SQLQueryEngine(metaDataStore, null));
+                () -> new SQLQueryEngine(metaDataStore, null, null));
         assertEquals(
                 "Formula reference loop found: loop.highScore->loop.highScore",
                 exception.getMessage());

elide-datastore/elide-datastore-aggregation/src/test/java/com/yahoo/elide/datastores/aggregation/framework/AggregationDataStoreTestHarness.java

@@ -28,7 +28,7 @@ public AggregationDataStoreTestHarness(EntityManagerFactory entityManagerFactory
     public DataStore getDataStore() {
         MetaDataStore metaDataStore = new MetaDataStore();
 
-        QueryEngine sqlQueryEngine = new SQLQueryEngine(metaDataStore, entityManagerFactory);
+        QueryEngine sqlQueryEngine = new SQLQueryEngine(metaDataStore, entityManagerFactory, null);
 
         AggregationDataStore aggregationDataStore = new AggregationDataStore(sqlQueryEngine);
 

elide-datastore/elide-datastore-aggregation/src/test/java/com/yahoo/elide/datastores/aggregation/framework/SQLUnitTest.java

@@ -67,7 +67,7 @@ public static void init() {
 
         metaDataStore.populateEntityDictionary(dictionary);
 
-        engine = new SQLQueryEngine(metaDataStore, emf);
+        engine = new SQLQueryEngine(metaDataStore, emf, null);
         playerStatsTable = engine.getTable("playerStats");
 
         ASIA.setName("Asia");