Github user hbdeshmukh commented on a diff in the pull request:
https://github.com/apache/incubator-quickstep/pull/121#discussion_r84796051
--- Diff: storage/PartitionedHashTablePool.hpp ---
@@ -0,0 +1,224 @@
+/**
+ * Copyright 2016, Quickstep Research Group, Computer Sciences
Department,
+ * University of WisconsinâMadison.
+ *
+ * Licensed 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.
+ **/
+
+#ifndef QUICKSTEP_STORAGE_PARTITIONED_HASH_TABLE_POOL_HPP_
+#define QUICKSTEP_STORAGE_PARTITIONED_HASH_TABLE_POOL_HPP_
+
+#include <algorithm>
+#include <chrono>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "expressions/aggregation/AggregationHandle.hpp"
+#include "storage/HashTableBase.hpp"
+#include "storage/FastHashTable.hpp"
+#include "storage/FastHashTableFactory.hpp"
+#include "utility/Macros.hpp"
+#include "utility/StringUtil.hpp"
+
+#include "glog/logging.h"
+
+namespace quickstep {
+
+class StorageManager;
+class Type;
+
+/** \addtogroup Storage
+ * @{
+ */
+
+/**
+ * @brief A pool of HashTables used for a single aggregation handle. Each
+ * HashTable represents values from a given partition, which is
+ * determined by the keys in the group by clause.
+ **/
+class PartitionedHashTablePool {
+ public:
+ /**
+ * @brief Constructor.
+ *
+ * @param estimated_num_entries The maximum number of entries in a hash
table.
+ * @param num_partitions The number of partitions (i.e. number of
HashTables)
+ * @param hash_table_impl_type The type of hash table implementation.
+ * @param group_by_types A vector of pointer of types which form the
group by
+ * key.
+ * @param agg_handle The aggregation handle.
+ * @param storage_manager A pointer to the storage manager.
+ *
+ * @note The estimate of number of entries is quite inaccurate at this
time.
+ * If we go by the current estimate, each hash table demands much
+ * larger space than it actually needs, which causes the system to
+ * either trigger evictions or worse - run out of memory. To fix
this
+ * issue, we divide the estimate by 100. The division will not
affect
+ * correctness, however it may allocate some hash tables smaller
space
+ * than their requirement, causing them to be resized during build
+ * phase, which has a performance penalty.
+ **/
+ PartitionedHashTablePool(const std::size_t estimated_num_entries,
+ const std::size_t num_partitions,
+ const HashTableImplType hash_table_impl_type,
+ const std::vector<const Type *> &group_by_types,
+ AggregationHandle *agg_handle,
+ StorageManager *storage_manager)
+ : estimated_num_entries_(
+ setHashTableSize(estimated_num_entries, num_partitions)),
+ num_partitions_(num_partitions),
+ hash_table_impl_type_(hash_table_impl_type),
+ group_by_types_(group_by_types),
+ agg_handle_(DCHECK_NOTNULL(agg_handle)),
+ storage_manager_(DCHECK_NOTNULL(storage_manager)) {
+ initializeAllHashTables();
+ }
+
+ /**
+ * @brief Constructor.
+ *
+ * @note This constructor is relevant for the HashTable specialized for
+ * aggregation.
+ *
+ * @param estimated_num_entries The maximum number of entries in a hash
table.
+ * @param num_partitions The number of partitions (i.e. number of
HashTables)
+ * @param hash_table_impl_type The type of hash table implementation.
+ * @param group_by_types A vector of pointer of types which form the
group by
+ * key.
+ * @param payload_sizes The sizes of the payload elements (i.e.
+ * AggregationStates).
+ * @param handles The aggregation handles.
+ * @param storage_manager A pointer to the storage manager.
+ **/
+ PartitionedHashTablePool(const std::size_t estimated_num_entries,
+ const std::size_t num_partitions,
+ const HashTableImplType hash_table_impl_type,
+ const std::vector<const Type *> &group_by_types,
+ const std::vector<std::size_t> &payload_sizes,
+ const std::vector<AggregationHandle *> &handles,
+ StorageManager *storage_manager)
+ : estimated_num_entries_(
+ setHashTableSize(estimated_num_entries, num_partitions)),
+ num_partitions_(num_partitions),
+ hash_table_impl_type_(hash_table_impl_type),
+ group_by_types_(group_by_types),
+ payload_sizes_(payload_sizes),
+ handles_(handles),
+ storage_manager_(DCHECK_NOTNULL(storage_manager)) {
+ initializeAllHashTables();
+ }
+
+ /**
+ * @brief Check out a hash table for insertion.
+ *
+ * @param partition_id The ID of the partitioned HashTable.
+ *
+ * @return A hash table pointer for the given HashTable.
+ **/
+ AggregationStateHashTableBase* getHashTable(const std::size_t
partition_id) {
+ DCHECK_LT(partition_id, num_partitions_);
+ DCHECK_LT(partition_id, hash_tables_.size());
+ return hash_tables_[partition_id].get();
+ }
+
+ /**
+ * @brief Check out a hash table for insertion.
+ *
+ * @param partition_id The ID of the partitioned HashTable.
+ *
+ * @return A hash table pointer for the given HashTable.
+ **/
+ AggregationStateHashTableBase* getHashTableFast(const std::size_t
partition_id) {
--- End diff --
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