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rocksdb/db/range_del_aggregator.h

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// Copyright (c) 2016-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 <map>
#include <set>
#include <string>
#include <vector>
#include "db/compaction_iteration_stats.h"
#include "db/dbformat.h"
#include "db/pinned_iterators_manager.h"
#include "db/version_edit.h"
#include "include/rocksdb/comparator.h"
#include "include/rocksdb/types.h"
#include "table/internal_iterator.h"
#include "table/scoped_arena_iterator.h"
#include "table/table_builder.h"
#include "util/kv_map.h"
namespace rocksdb {
// RangeDelMaps maintain position across calls to ShouldDelete. The caller may
// wish to specify a mode to optimize positioning the iterator during the next
// call to ShouldDelete. The non-kFullScan modes are only available when
// deletion collapsing is enabled.
//
// For example, if we invoke Next() on an iterator, kForwardTraversal should be
// specified to advance one-by-one through deletions until one is found with its
// interval containing the key. This will typically be faster than doing a full
// binary search (kBinarySearch).
enum class RangeDelPositioningMode {
kFullScan, // used iff collapse_deletions_ == false
kForwardTraversal,
kBackwardTraversal,
kBinarySearch,
};
// A RangeDelIterator iterates over range deletion tombstones.
class RangeDelIterator {
public:
virtual ~RangeDelIterator() = default;
virtual bool Valid() const = 0;
virtual void Next() = 0;
virtual void Seek(const Slice& target) = 0;
virtual RangeTombstone Tombstone() const = 0;
};
// A RangeDelMap keeps track of range deletion tombstones within a snapshot
// stripe.
//
// RangeDelMaps are used internally by RangeDelAggregator. They are not intended
// to be used directly.
class RangeDelMap {
public:
virtual ~RangeDelMap() = default;
virtual bool ShouldDelete(const ParsedInternalKey& parsed,
RangeDelPositioningMode mode) = 0;
virtual bool IsRangeOverlapped(const Slice& start, const Slice& end) = 0;
virtual void InvalidatePosition() = 0;
virtual size_t Size() const = 0;
bool IsEmpty() const { return Size() == 0; }
virtual void AddTombstone(RangeTombstone tombstone) = 0;
virtual std::unique_ptr<RangeDelIterator> NewIterator() = 0;
};
// A RangeDelAggregator aggregates range deletion tombstones as they are
// encountered in memtables/SST files. It provides methods that check whether a
// key is covered by range tombstones or write the relevant tombstones to a new
// SST file.
class RangeDelAggregator {
public:
// @param snapshots These are used to organize the tombstones into snapshot
// stripes, which is the seqnum range between consecutive snapshots,
// including the higher snapshot and excluding the lower one. Currently,
// this is used by ShouldDelete() to prevent deletion of keys that are
// covered by range tombstones in other snapshot stripes. This constructor
// is used for writes (flush/compaction). All DB snapshots are provided
// such that no keys are removed that are uncovered according to any DB
// snapshot.
// Note this overload does not lazily initialize Rep.
RangeDelAggregator(const InternalKeyComparator& icmp,
const std::vector<SequenceNumber>& snapshots,
bool collapse_deletions = true);
// @param upper_bound Similar to snapshots above, except with a single
// snapshot, which allows us to store the snapshot on the stack and defer
// initialization of heap-allocating members (in Rep) until the first range
// deletion is encountered. This constructor is used in case of reads (get/
// iterator), for which only the user snapshot (upper_bound) is provided
// such that the seqnum space is divided into two stripes. Only the older
// stripe will be used by ShouldDelete().
RangeDelAggregator(const InternalKeyComparator& icmp,
SequenceNumber upper_bound,
bool collapse_deletions = false);
// Returns whether the key should be deleted, which is the case when it is
// covered by a range tombstone residing in the same snapshot stripe.
// @param mode If collapse_deletions_ is true, this dictates how we will find
// the deletion whose interval contains this key. Otherwise, its
// value must be kFullScan indicating linear scan from beginning..
bool ShouldDelete(
const ParsedInternalKey& parsed,
RangeDelPositioningMode mode = RangeDelPositioningMode::kFullScan) {
if (rep_ == nullptr) {
return false;
}
return ShouldDeleteImpl(parsed, mode);
}
bool ShouldDelete(
const Slice& internal_key,
RangeDelPositioningMode mode = RangeDelPositioningMode::kFullScan) {
if (rep_ == nullptr) {
return false;
}
return ShouldDeleteImpl(internal_key, mode);
}
bool ShouldDeleteImpl(const ParsedInternalKey& parsed,
RangeDelPositioningMode mode);
bool ShouldDeleteImpl(const Slice& internal_key,
RangeDelPositioningMode mode);
// Checks whether range deletions cover any keys between `start` and `end`,
// inclusive.
//
// @param start User key representing beginning of range to check for overlap.
// @param end User key representing end of range to check for overlap. This
// argument is inclusive, so the existence of a range deletion covering
// `end` causes this to return true.
bool IsRangeOverlapped(const Slice& start, const Slice& end);
// Adds tombstones to the tombstone aggregation structure maintained by this
// object. Tombstones are truncated to smallest and largest. If smallest (or
// largest) is null, it is not used for truncation. When adding range
// tombstones present in an sstable, smallest and largest should be set to
// the smallest and largest keys from the sstable file metadata. Note that
// tombstones end keys are exclusive while largest is inclusive.
// @return non-OK status if any of the tombstone keys are corrupted.
Status AddTombstones(std::unique_ptr<InternalIterator> input,
const InternalKey* smallest = nullptr,
const InternalKey* largest = nullptr);
// Resets iterators maintained across calls to ShouldDelete(). This may be
// called when the tombstones change, or the owner may call explicitly, e.g.,
// if it's an iterator that just seeked to an arbitrary position. The effect
// of invalidation is that the following call to ShouldDelete() will binary
// search for its tombstone.
void InvalidateRangeDelMapPositions();
bool IsEmpty();
bool AddFile(uint64_t file_number);
// Create a new iterator over the range deletion tombstones in all of the
// snapshot stripes in this aggregator. Tombstones are presented in start key
// order. Tombstones with the same start key are presented in arbitrary order.
//
// The iterator is invalidated after any call to AddTombstones. It is the
// caller's responsibility to avoid using invalid iterators.
std::unique_ptr<RangeDelIterator> NewIterator();
private:
// Maps snapshot seqnum -> map of tombstones that fall in that stripe, i.e.,
// their seqnums are greater than the next smaller snapshot's seqnum.
typedef std::map<SequenceNumber, std::unique_ptr<RangeDelMap>> StripeMap;
struct Rep {
StripeMap stripe_map_;
PinnedIteratorsManager pinned_iters_mgr_;
std::set<uint64_t> added_files_;
};
// Initializes rep_ lazily. This aggregator object is constructed for every
// read, so expensive members should only be created when necessary, i.e.,
// once the first range deletion is encountered.
void InitRep(const std::vector<SequenceNumber>& snapshots);
std::unique_ptr<RangeDelMap> NewRangeDelMap();
RangeDelMap& GetRangeDelMap(SequenceNumber seq);
SequenceNumber upper_bound_;
std::unique_ptr<Rep> rep_;
const InternalKeyComparator& icmp_;
// collapse range deletions so they're binary searchable
const bool collapse_deletions_;
};
} // namespace rocksdb