fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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147 lines
6.4 KiB
147 lines
6.4 KiB
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include <memory>
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#include "db/range_tombstone_fragmenter.h"
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#include "rocksdb/slice_transform.h"
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#include "table/get_context.h"
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#include "table/internal_iterator.h"
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#include "table/multiget_context.h"
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#include "table/table_reader_caller.h"
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namespace ROCKSDB_NAMESPACE {
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class Iterator;
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struct ParsedInternalKey;
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class Slice;
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class Arena;
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struct ReadOptions;
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struct TableProperties;
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class GetContext;
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class MultiGetContext;
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// A Table (also referred to as SST) is a sorted map from strings to strings.
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// Tables are immutable and persistent. A Table may be safely accessed from
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// multiple threads without external synchronization. Table readers are used
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// for reading various types of table formats supported by rocksdb including
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// BlockBasedTable, PlainTable and CuckooTable format.
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class TableReader {
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public:
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virtual ~TableReader() {}
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// Returns a new iterator over the table contents.
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// The result of NewIterator() is initially invalid (caller must
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// call one of the Seek methods on the iterator before using it).
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//
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// read_options: Must outlive the returned iterator.
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// arena: If not null, the arena needs to be used to allocate the Iterator.
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// When destroying the iterator, the caller will not call "delete"
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// but Iterator::~Iterator() directly. The destructor needs to destroy
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// all the states but those allocated in arena.
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// skip_filters: disables checking the bloom filters even if they exist. This
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// option is effective only for block-based table format.
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// compaction_readahead_size: its value will only be used if caller =
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// kCompaction
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virtual InternalIterator* NewIterator(
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const ReadOptions& read_options, const SliceTransform* prefix_extractor,
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Arena* arena, bool skip_filters, TableReaderCaller caller,
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size_t compaction_readahead_size = 0,
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bool allow_unprepared_value = false) = 0;
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virtual FragmentedRangeTombstoneIterator* NewRangeTombstoneIterator(
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const ReadOptions& /*read_options*/) {
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return nullptr;
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}
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// Given a key, return an approximate byte offset in the file where
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// the data for that key begins (or would begin if the key were
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// present in the file). The returned value is in terms of file
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// bytes, and so includes effects like compression of the underlying data.
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// E.g., the approximate offset of the last key in the table will
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// be close to the file length.
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// TODO(peterd): Since this function is only used for approximate size
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// from beginning of file, reduce code duplication by removing this
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// function and letting ApproximateSize take optional start and end, so
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// that absolute start and end can be specified and optimized without
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// key / index work.
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virtual uint64_t ApproximateOffsetOf(const Slice& key,
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TableReaderCaller caller) = 0;
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// Given start and end keys, return the approximate data size in the file
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// between the keys. The returned value is in terms of file bytes, and so
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// includes effects like compression of the underlying data and applicable
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// portions of metadata including filters and indexes. Nullptr for start or
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// end (or both) indicates absolute start or end of the table.
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virtual uint64_t ApproximateSize(const Slice& start, const Slice& end,
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TableReaderCaller caller) = 0;
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// Set up the table for Compaction. Might change some parameters with
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// posix_fadvise
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virtual void SetupForCompaction() = 0;
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virtual std::shared_ptr<const TableProperties> GetTableProperties() const = 0;
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// Prepare work that can be done before the real Get()
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virtual void Prepare(const Slice& /*target*/) {}
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// Report an approximation of how much memory has been used.
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virtual size_t ApproximateMemoryUsage() const = 0;
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// Calls get_context->SaveValue() repeatedly, starting with
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// the entry found after a call to Seek(key), until it returns false.
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// May not make such a call if filter policy says that key is not present.
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//
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// get_context->MarkKeyMayExist needs to be called when it is configured to be
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// memory only and the key is not found in the block cache.
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//
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// readOptions is the options for the read
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// key is the key to search for
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// skip_filters: disables checking the bloom filters even if they exist. This
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// option is effective only for block-based table format.
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virtual Status Get(const ReadOptions& readOptions, const Slice& key,
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GetContext* get_context,
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const SliceTransform* prefix_extractor,
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bool skip_filters = false) = 0;
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virtual void MultiGet(const ReadOptions& readOptions,
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const MultiGetContext::Range* mget_range,
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const SliceTransform* prefix_extractor,
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bool skip_filters = false) {
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for (auto iter = mget_range->begin(); iter != mget_range->end(); ++iter) {
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*iter->s = Get(readOptions, iter->ikey, iter->get_context,
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prefix_extractor, skip_filters);
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}
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}
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// Prefetch data corresponding to a give range of keys
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// Typically this functionality is required for table implementations that
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// persists the data on a non volatile storage medium like disk/SSD
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virtual Status Prefetch(const Slice* begin = nullptr,
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const Slice* end = nullptr) {
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(void) begin;
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(void) end;
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// Default implementation is NOOP.
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// The child class should implement functionality when applicable
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return Status::OK();
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}
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// convert db file to a human readable form
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virtual Status DumpTable(WritableFile* /*out_file*/) {
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return Status::NotSupported("DumpTable() not supported");
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}
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// check whether there is corruption in this db file
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virtual Status VerifyChecksum(const ReadOptions& /*read_options*/,
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TableReaderCaller /*caller*/) {
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return Status::NotSupported("VerifyChecksum() not supported");
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}
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};
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} // namespace ROCKSDB_NAMESPACE
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