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rocksdb/include/leveldb/memtablerep.h

88 lines
2.8 KiB

// This file contains the interface that must be implemented by any collection
// to be used as the backing store for a MemTable. Such a collection must
// satisfy the following properties:
// (1) It does not store duplicate items.
// (2) It uses MemTableRep::KeyComparator to compare items for iteration and
// equality.
// (3) It can be accessed concurrently by multiple readers but need not support
// concurrent writes.
// (4) Items are never deleted.
// The liberal use of assertions is encouraged to enforce (1).
#ifndef STORAGE_LEVELDB_DB_TABLE_H_
#define STORAGE_LEVELDB_DB_TABLE_H_
#include <memory>
#include "leveldb/arena.h"
namespace leveldb {
class MemTableRep {
public:
// KeyComparator(a, b) returns a negative value if a is less than b, 0 if they
// are equal, and a positive value if b is greater than a
class KeyComparator {
public:
virtual int operator()(const char* a, const char* b) const = 0;
virtual ~KeyComparator() { }
};
// Insert key into the collection. (The caller will pack key and value into a
// single buffer and pass that in as the parameter to Insert)
// REQUIRES: nothing that compares equal to key is currently in the
// collection.
virtual void Insert(const char* key) = 0;
// Returns true iff an entry that compares equal to key is in the collection.
virtual bool Contains(const char* key) const = 0;
virtual ~MemTableRep() { }
// Iteration over the contents of a skip collection
class Iterator {
public:
// Initialize an iterator over the specified collection.
// The returned iterator is not valid.
// explicit Iterator(const MemTableRep* collection);
virtual ~Iterator() { };
// Returns true iff the iterator is positioned at a valid node.
virtual bool Valid() const = 0;
// Returns the key at the current position.
// REQUIRES: Valid()
virtual const char* key() const = 0;
// Advances to the next position.
// REQUIRES: Valid()
virtual void Next() = 0;
// Advances to the previous position.
// REQUIRES: Valid()
virtual void Prev() = 0;
// Advance to the first entry with a key >= target
virtual void Seek(const char* target) = 0;
// Position at the first entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToFirst() = 0;
// Position at the last entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToLast() = 0;
};
virtual std::shared_ptr<Iterator> GetIterator() = 0;
};
class MemTableRepFactory {
public:
virtual ~MemTableRepFactory() { };
virtual std::shared_ptr<MemTableRep> CreateMemTableRep(
MemTableRep::KeyComparator&, Arena* arena) = 0;
};
}
#endif // STORAGE_LEVELDB_DB_TABLE_H_