ajantha-bhat commented on a change in pull request #3908:
URL: https://github.com/apache/carbondata/pull/3908#discussion_r486970553



##########
File path: 
integration/spark/src/main/scala/org/apache/spark/util/PartitionCacheManager.scala
##########
@@ -0,0 +1,181 @@
+/*
+ * 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.util
+
+import java.net.URI
+import java.util
+
+import scala.collection.JavaConverters._
+import scala.collection.mutable
+
+import org.apache.log4j.Logger
+import org.apache.spark.sql.catalyst.catalog.{CatalogStorageFormat, 
CatalogTablePartition}
+
+import org.apache.carbondata.common.logging.LogServiceFactory
+import org.apache.carbondata.core.cache.{Cache, Cacheable, CarbonLRUCache}
+import org.apache.carbondata.core.constants.CarbonCommonConstants
+import org.apache.carbondata.core.datastore.impl.FileFactory
+import org.apache.carbondata.core.index.Segment
+import org.apache.carbondata.core.metadata.{AbsoluteTableIdentifier, 
SegmentFileStore}
+import org.apache.carbondata.core.statusmanager.{LoadMetadataDetails, 
SegmentStatusManager}
+import org.apache.carbondata.core.util.path.CarbonTablePath
+
+object PartitionCacheManager extends Cache[PartitionCacheKey,
+  java.util.List[CatalogTablePartition]] {
+
+  private val CACHE = new CarbonLRUCache(
+    CarbonCommonConstants.CARBON_PARTITION_MAX_DRIVER_LRU_CACHE_SIZE,
+    CarbonCommonConstants.CARBON_MAX_LRU_CACHE_SIZE_DEFAULT)
+
+  val LOGGER: Logger = LogServiceFactory.getLogService(this.getClass.getName)
+
+  def get(identifier: PartitionCacheKey): 
java.util.List[CatalogTablePartition] = {
+    LOGGER.info("Reading partition values from store")
+    // read the tableStatus file to get valid and invalid segments
+    val validInvalidSegments = new 
SegmentStatusManager(AbsoluteTableIdentifier.from(
+      identifier.tablePath, null, null, identifier.tableId))
+      .getValidAndInvalidSegments
+    val cacheablePartitionSpecs = 
validInvalidSegments.getValidSegments.asScala.map { segment =>
+      val segmentFileName = segment.getSegmentFileName
+      val segmentFilePath = FileFactory.getCarbonFile(
+        CarbonTablePath.getSegmentFilePath(identifier.tablePath, 
segmentFileName))
+      // read the last modified time
+      val segmentFileModifiedTime = segmentFilePath.getLastModifiedTime
+      val existingCache = CACHE.get(identifier.tableId)
+      if (existingCache != null) {
+        val segmentCache = 
CACHE.get(identifier.tableId).asInstanceOf[CacheablePartitionSpec]
+          .partitionSpecs.get(segment.getSegmentNo)
+        segmentCache match {
+          case Some(c) =>
+            // check if cache needs to be updated
+            if (segmentFileModifiedTime > c._2) {
+              (segment.getSegmentNo, (readPartition(identifier,
+                segmentFilePath.getAbsolutePath), segmentFileModifiedTime))
+            } else {
+              (segment.getSegmentNo, c)
+            }
+          case None =>
+            (segment.getSegmentNo, (readPartition(identifier,
+              segmentFilePath.getAbsolutePath), segmentFileModifiedTime))
+        }
+      } else {
+        // read the partitions if not available in cache.
+        (segment.getSegmentNo, (readPartition(identifier,

Review comment:
       readPartition reads the segment file. 
   so basically first time we read all the segment files of the table.
   
   I have seen the users with 200K segments in one table stored in cloud. query 
takes more than 5 hours for them if we do this.
   
   So, need to change the key as partition spec and cache only matched 
partitions
   
   @kumarvishal09 , @QiangCai @marchpure : what is your opinion on this ?




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