mirror of https://gitee.com/bigwinds/arangodb
119 lines
4.3 KiB
C++
119 lines
4.3 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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/// DISCLAIMER
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///
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/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
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/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
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///
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/// Licensed under the Apache License, Version 2.0 (the "License");
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/// you may not use this file except in compliance with the License.
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/// You may obtain a copy of the License at
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///
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/// http://www.apache.org/licenses/LICENSE-2.0
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///
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/// Unless required by applicable law or agreed to in writing, software
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/// distributed under the License is distributed on an "AS IS" BASIS,
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/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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/// See the License for the specific language governing permissions and
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/// limitations under the License.
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///
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/// Copyright holder is ArangoDB GmbH, Cologne, Germany
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///
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/// @author Jan Steemann
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////////////////////////////////////////////////////////////////////////////////
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#ifndef ARANGOD_READ_CACHE_GLOBAL_REVISION_CACHE_H
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#define ARANGOD_READ_CACHE_GLOBAL_REVISION_CACHE_H 1
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#include "Basics/Common.h"
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#include "Basics/ReadWriteLock.h"
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#include "ReadCache/RevisionReader.h"
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#include <velocypack/Slice.h>
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namespace arangodb {
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class GlobalGlobalRevisionCacheChunk;
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// the global revision cache for documents
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class GlobalRevisionCache {
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public:
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GlobalRevisionCache() = delete;
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GlobalRevisionCache(GlobalRevisionCache const&) = delete;
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GlobalRevisionCache& operator=(GlobalRevisionCache const&) = delete;
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// create the cache instance
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GlobalRevisionCache(size_t defaultChunkSize, size_t totalTargetSize, GarbageCollectionCallback const& callback);
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// destroy the cache instance
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~GlobalRevisionCache();
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// total number of bytes allocated by the cache
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size_t totalAllocated();
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// stores a revision in the read-cache, acquiring a lease
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// the collection id is prepended to the actual data in order to quickly access
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// the shard-local hash for the revision when cleaning up the chunk
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RevisionReader storeAndLease(uint64_t collectionId, uint8_t const* data, size_t length);
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// stores a revision in the read-cache, acquiring a lease
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RevisionReader storeAndLease(uint64_t collectionId, arangodb::velocypack::Slice const& data) {
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// simply forward to the pointer-based function
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return storeAndLease(collectionId, data.begin(), data.byteSize());
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}
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// stores a revision in the read-cache, without acquiring a lease
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void store(uint64_t collectionId, uint8_t const* data, size_t length);
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// stores a revision in the read-cache, without acquiring a lease
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void store(uint64_t collectionId, arangodb::velocypack::Slice const& data) {
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// simply forward to the pointer-based function
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return store(collectionId, data.begin(), data.byteSize());
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}
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// run the garbage collection with the intent to free unused chunks
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bool garbageCollect();
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private:
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// garbage collects a single chunk
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bool garbageCollect(std::unique_ptr<GlobalRevisionCacheChunk>& chunk);
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// calculate the size for a new chunk
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size_t newChunkSize(size_t dataLength) const noexcept;
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// adds a new chunk, capable of storing at least dataLength
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// additionally this will move fullChunk into the used list if it is still
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// contained in the free list
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void addChunk(size_t dataLength, GlobalRevisionCacheChunk* fullChunk);
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// creates a chunk, or uses an existing one from the cache
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GlobalRevisionCacheChunk* buildChunk(size_t targetSize);
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private:
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// lock for the lists of chunks
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arangodb::basics::ReadWriteLock _chunksLock;
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// filled chunks in a doubly-linked list, with most recently accessed
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// chunks at the head of the list. the chunks at the tail of the list
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// are subject to garbage collection!
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std::unordered_set<GlobalRevisionCacheChunk*> _usedList;
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// completely (or partially unused) chunks that can still be written to
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std::vector<GlobalRevisionCacheChunk*> _freeList;
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// default size for new memory chunks
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size_t _defaultChunkSize;
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// total target size for all chunks
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size_t _totalTargetSize;
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// total number of bytes allocated by chunks
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size_t _totalAllocated;
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// callback function for garbage collection
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GarbageCollectionCallback _callback;
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};
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}
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#endif
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