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rocksdb/table/get_context.h

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8.8 KiB

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#pragma once
#include <string>
#include "db/read_callback.h"
#include "rocksdb/types.h"
namespace ROCKSDB_NAMESPACE {
class BlobFetcher;
class Comparator;
class Logger;
class MergeContext;
class MergeOperator;
class PinnedIteratorsManager;
class Statistics;
class SystemClock;
struct ParsedInternalKey;
// Data structure for accumulating statistics during a point lookup. At the
// end of the point lookup, the corresponding ticker stats are updated. This
// avoids the overhead of frequent ticker stats updates
struct GetContextStats {
uint64_t num_cache_hit = 0;
uint64_t num_cache_index_hit = 0;
uint64_t num_cache_data_hit = 0;
uint64_t num_cache_filter_hit = 0;
uint64_t num_cache_compression_dict_hit = 0;
uint64_t num_cache_index_miss = 0;
uint64_t num_cache_filter_miss = 0;
uint64_t num_cache_data_miss = 0;
uint64_t num_cache_compression_dict_miss = 0;
uint64_t num_cache_bytes_read = 0;
uint64_t num_cache_miss = 0;
uint64_t num_cache_add = 0;
uint64_t num_cache_add_redundant = 0;
uint64_t num_cache_bytes_write = 0;
uint64_t num_cache_index_add = 0;
uint64_t num_cache_index_add_redundant = 0;
uint64_t num_cache_index_bytes_insert = 0;
uint64_t num_cache_data_add = 0;
uint64_t num_cache_data_add_redundant = 0;
uint64_t num_cache_data_bytes_insert = 0;
uint64_t num_cache_filter_add = 0;
uint64_t num_cache_filter_add_redundant = 0;
uint64_t num_cache_filter_bytes_insert = 0;
uint64_t num_cache_compression_dict_add = 0;
uint64_t num_cache_compression_dict_add_redundant = 0;
uint64_t num_cache_compression_dict_bytes_insert = 0;
// MultiGet stats.
uint64_t num_filter_read = 0;
uint64_t num_index_read = 0;
uint64_t num_sst_read = 0;
};
// A class to hold context about a point lookup, such as pointer to value
// slice, key, merge context etc, as well as the current state of the
// lookup. Any user using GetContext to track the lookup result must call
// SaveValue() whenever the internal key is found. This can happen
// repeatedly in case of merge operands. In case the key may exist with
// high probability, but IO is required to confirm and the user doesn't allow
// it, MarkKeyMayExist() must be called instead of SaveValue().
class GetContext {
public:
// Current state of the point lookup. All except kNotFound and kMerge are
// terminal states
enum GetState {
kNotFound,
kFound,
kDeleted,
kCorrupt,
kMerge, // saver contains the current merge result (the operands)
kUnexpectedBlobIndex,
// TODO: remove once wide-column entities are supported by Get/MultiGet
kUnexpectedWideColumnEntity,
};
GetContextStats get_context_stats_;
// Constructor
// @param value Holds the value corresponding to user_key. If its nullptr
// then return all merge operands corresponding to user_key
// via merge_context
// @param value_found If non-nullptr, set to false if key may be present
// but we can't be certain because we cannot do IO
// @param max_covering_tombstone_seq Pointer to highest sequence number of
// range deletion covering the key. When an internal key
// is found with smaller sequence number, the lookup
// terminates
// @param seq If non-nullptr, the sequence number of the found key will be
// saved here
// @param callback Pointer to ReadCallback to perform additional checks
// for visibility of a key
// @param is_blob_index If non-nullptr, will be used to indicate if a found
// key is of type blob index
// @param do_merge True if value associated with user_key has to be returned
// and false if all the merge operands associated with user_key has to be
// returned. Id do_merge=false then all the merge operands are stored in
// merge_context and they are never merged. The value pointer is untouched.
GetContext(const Comparator* ucmp, const MergeOperator* merge_operator,
Logger* logger, Statistics* statistics, GetState init_state,
const Slice& user_key, PinnableSlice* value, bool* value_found,
MergeContext* merge_context, bool do_merge,
SequenceNumber* max_covering_tombstone_seq, SystemClock* clock,
SequenceNumber* seq = nullptr,
PinnedIteratorsManager* _pinned_iters_mgr = nullptr,
ReadCallback* callback = nullptr, bool* is_blob_index = nullptr,
uint64_t tracing_get_id = 0, BlobFetcher* blob_fetcher = nullptr);
GetContext(const Comparator* ucmp, const MergeOperator* merge_operator,
Logger* logger, Statistics* statistics, GetState init_state,
const Slice& user_key, PinnableSlice* value,
std::string* timestamp, bool* value_found,
MergeContext* merge_context, bool do_merge,
SequenceNumber* max_covering_tombstone_seq, SystemClock* clock,
SequenceNumber* seq = nullptr,
PinnedIteratorsManager* _pinned_iters_mgr = nullptr,
ReadCallback* callback = nullptr, bool* is_blob_index = nullptr,
uint64_t tracing_get_id = 0, BlobFetcher* blob_fetcher = nullptr);
GetContext() = delete;
// This can be called to indicate that a key may be present, but cannot be
// confirmed due to IO not allowed
void MarkKeyMayExist();
// Records this key, value, and any meta-data (such as sequence number and
// state) into this GetContext.
//
// If the parsed_key matches the user key that we are looking for, sets
// matched to true.
//
// Returns True if more keys need to be read (due to merges) or
// False if the complete value has been found.
bool SaveValue(const ParsedInternalKey& parsed_key, const Slice& value,
bool* matched, Cleanable* value_pinner = nullptr);
// Simplified version of the previous function. Should only be used when we
// know that the operation is a Put.
void SaveValue(const Slice& value, SequenceNumber seq);
GetState State() const { return state_; }
SequenceNumber* max_covering_tombstone_seq() {
return max_covering_tombstone_seq_;
}
PinnedIteratorsManager* pinned_iters_mgr() { return pinned_iters_mgr_; }
// If a non-null string is passed, all the SaveValue calls will be
// logged into the string. The operations can then be replayed on
// another GetContext with replayGetContextLog.
void SetReplayLog(std::string* replay_log) { replay_log_ = replay_log; }
// Do we need to fetch the SequenceNumber for this key?
bool NeedToReadSequence() const { return (seq_ != nullptr); }
bool sample() const { return sample_; }
bool CheckCallback(SequenceNumber seq) {
if (callback_) {
return callback_->IsVisible(seq);
}
return true;
}
void ReportCounters();
bool has_callback() const { return callback_ != nullptr; }
uint64_t get_tracing_get_id() const { return tracing_get_id_; }
void push_operand(const Slice& value, Cleanable* value_pinner);
private:
void Merge(const Slice* value);
bool GetBlobValue(const Slice& blob_index, PinnableSlice* blob_value);
const Comparator* ucmp_;
const MergeOperator* merge_operator_;
// the merge operations encountered;
Logger* logger_;
Statistics* statistics_;
GetState state_;
Slice user_key_;
PinnableSlice* pinnable_val_;
std::string* timestamp_;
bool* value_found_; // Is value set correctly? Used by KeyMayExist
MergeContext* merge_context_;
SequenceNumber* max_covering_tombstone_seq_;
SystemClock* clock_;
// If a key is found, seq_ will be set to the SequenceNumber of most recent
// write to the key or kMaxSequenceNumber if unknown
SequenceNumber* seq_;
std::string* replay_log_;
// Used to temporarily pin blocks when state_ == GetContext::kMerge
PinnedIteratorsManager* pinned_iters_mgr_;
ReadCallback* callback_;
bool sample_;
// Value is true if it's called as part of DB Get API and false if it's
// called as part of DB GetMergeOperands API. When it's false merge operators
// are never merged.
bool do_merge_;
bool* is_blob_index_;
// Used for block cache tracing only. A tracing get id uniquely identifies a
// Get or a MultiGet.
const uint64_t tracing_get_id_;
BlobFetcher* blob_fetcher_;
};
// Call this to replay a log and bring the get_context up to date. The replay
// log must have been created by another GetContext object, whose replay log
// must have been set by calling GetContext::SetReplayLog().
void replayGetContextLog(const Slice& replay_log, const Slice& user_key,
GetContext* get_context,
Cleanable* value_pinner = nullptr);
} // namespace ROCKSDB_NAMESPACE