Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/2501#discussion_r18081225
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/CacheManager.scala
---
@@ -0,0 +1,126 @@
+/*
+ * 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.spark.sql
+
+import java.util.concurrent.locks.ReentrantReadWriteLock
+
+import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
+import org.apache.spark.sql.columnar.InMemoryRelation
+import org.apache.spark.storage.StorageLevel
+import org.apache.spark.storage.StorageLevel.MEMORY_ONLY
+
+/** Holds a cached logical plan and its data */
+private case class CachedData(plan: LogicalPlan, cachedRepresentation:
InMemoryRelation)
+
+/**
+ * Provides support in a SQLContext for caching query results and
automatically using these cached
+ * results when subsequent queries are executed. Data is cached using
byte buffers stored in an
+ * InMemoryRelation. This relation is automatically substituted query
plans that return the
+ * `sameResult` as the originally cached query.
+ */
+private[sql] trait CacheManager {
+ self: SQLContext =>
+
+ @transient
+ private val cachedData = new
scala.collection.mutable.ArrayBuffer[CachedData]
+
+ @transient
+ private val cacheLock = new ReentrantReadWriteLock
+
+ /** Returns true if the table is currently cached in-memory. */
+ def isCached(tableName: String): Boolean =
lookupCachedData(table(tableName)).nonEmpty
+
+ /** Caches the specified table in-memory. */
+ def cacheTable(tableName: String): Unit = cacheQuery(table(tableName))
+
+ /** Removes the specified table from the in-memory cache. */
+ def uncacheTable(tableName: String): Unit =
uncacheQuery(table(tableName))
+
+ /** Acquires a read lock on the cache for the duration of `f`. */
+ private def readLock[A](f: => A): A = {
+ val lock = cacheLock.readLock()
+ lock.lock()
+ try f finally {
+ lock.unlock()
+ }
+ }
+
+ /** Acquires a write lock on the cache for the duration of `f`. */
+ private def writeLock[A](f: => A): A = {
+ val lock = cacheLock.writeLock()
+ lock.lock()
+ try f finally {
+ lock.unlock()
+ }
+ }
+
+ private[sql] def clearCache(): Unit = writeLock {
+ cachedData.foreach(_.cachedRepresentation.unpersist())
+ cachedData.clear()
+ }
+
+ /** Caches the data produced by the logical representation of the given
schema rdd. */
+ private[sql] def cacheQuery(
+ query: SchemaRDD,
+ storageLevel: StorageLevel = MEMORY_ONLY): Unit = writeLock {
+ val planToCache = query.queryExecution.optimizedPlan
+ if (lookupCachedData(planToCache).nonEmpty) {
+ logWarning("Asked to cache already cached data.")
+ } else {
+ cachedData +=
+ CachedData(
+ planToCache,
+ InMemoryRelation(
+ useCompression, columnBatchSize, storageLevel,
query.queryExecution.executedPlan))
+ }
+ }
+
+ /** Removes the data for the given SchemaRDD from the cache */
+ private[sql] def uncacheQuery(query: SchemaRDD, blocking: Boolean =
false): Unit = writeLock {
+ val planToCache = query.queryExecution.optimizedPlan
+ val dataIndex = cachedData.indexWhere(_.plan.sameResult(planToCache))
+
+ if (dataIndex < 0) {
+ throw new IllegalArgumentException(s"Table $query is not cached.")
+ }
+
+
cachedData(dataIndex).cachedRepresentation.cachedColumnBuffers.unpersist(blocking)
+ cachedData.remove(dataIndex)
+ }
+
+
+ /** Optionally returns cached data for the given SchemaRDD */
+ private[sql] def lookupCachedData(query: SchemaRDD): Option[CachedData]
= readLock {
+ lookupCachedData(query.queryExecution.optimizedPlan)
+ }
+
+ /** Optionally returns cached data for the given LogicalPlan. */
+ private[sql] def lookupCachedData(plan: LogicalPlan): Option[CachedData]
= readLock {
+ cachedData.find(_.plan.sameResult(plan))
+ }
+
+ /** Replaces segments of the given logical plan with cached versions
where possible. */
+ private[sql] def useCacheData(plan: LogicalPlan): LogicalPlan = {
--- End diff --
Should be renamed to `useCachedData`.
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