| // 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. |
| |
| #pragma once |
| |
| #include <memory> |
| #include <unordered_map> |
| #include <vector> |
| |
| #include <boost/thread/shared_mutex.hpp> |
| |
| namespace impala { |
| class MemTracker; |
| class ScanNode; |
| |
| /// Class to keep track of scanner threads for a query on the current backend. |
| /// Tracks the number of threads and their expected memory consumption |
| /// for the purpose of limiting the aggregate memory consumption of scanner threads. |
| /// This allows us to implement some heuristics that help prevent us going over the |
| /// query memory limit by creating too many scanner threads. |
| /// TODO: this can be removed once all scan nodes are switched to the MT versions. |
| class ScannerMemLimiter { |
| public: |
| ScannerMemLimiter(); |
| ~ScannerMemLimiter(); |
| |
| /// Register a scan and track the estimated memory 'estimated_initial_thread_mem' |
| /// for the initial threads. 'node' must live as long as this object is in use |
| /// (i.e. as long as the below methods are being called). Each 'node' can only |
| /// be registered once. |
| void RegisterScan(ScanNode* node, int64_t estimated_initial_thread_mem); |
| |
| /// Returns true if there is enough memory available to create a scanner thread |
| /// for node 'node_id' that is estimated to consume 'estimated_thread_mem' bytes |
| /// of memory. Updates the state of the limiter to reflect the increased memory. |
| /// The caller must call ReleaseMemoryForScannerThread() for every successful |
| /// call to this function. |
| bool ClaimMemoryForScannerThread(ScanNode* node, int64_t estimated_thread_mem); |
| |
| /// Must be called when a scanner thread exits. Releases the memory accounted for |
| /// by ClaimMemoryForScannerThread(). |
| void ReleaseMemoryForScannerThread(ScanNode* node, int64_t estimated_thread_mem); |
| |
| private: |
| struct RegisteredScan; |
| |
| /// Protects below data structures. |
| boost::shared_mutex registered_scans_lock_; |
| |
| /// All of this query's scan nodes. The scan nodes register themselves in their |
| /// Prepare() phase. Threads must hold 'registered_scans_lock_' in shared mode |
| /// when reading or in exclusive mode when modifying. The total memory currently |
| /// consumed by the scans is calculated by iterating over this map, which is |
| /// O(n) in the number of scans. With an unlimited number of thread tokens, |
| /// this would mean we do O(n^2) work per query, but in practice if there are a large |
| /// number of concurrent scans there will be no available thread tokens and |
| /// ClaimMemoryForScannerThread() will not be called. |
| std::unordered_map<ScanNode*, std::unique_ptr<RegisteredScan>> registered_scans_; |
| }; |
| } |