52d7ecfc78
Summary: This diff virtualizes the skiplist interface so that users can provide their own implementation of a backing store for MemTables. Eventually, the backing store will be responsible for its own synchronization, allowing users (and us) to experiment with different lockless implementations. Test Plan: make clean make -j32 check ./db_stress Reviewers: dhruba, emayanke, haobo Reviewed By: dhruba CC: leveldb Differential Revision: https://reviews.facebook.net/D11739
92 lines
2.8 KiB
C++
92 lines
2.8 KiB
C++
// This file contains the interface that must be implemented by any collection
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// to be used as the backing store for a MemTable. Such a collection must
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// satisfy the following properties:
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// (1) It does not store duplicate items.
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// (2) It uses MemTableRep::KeyComparator to compare items for iteration and
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// equality.
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// (3) It can be accessed concurrently by multiple readers but need not support
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// concurrent writes.
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// (4) Items are never deleted.
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// The liberal use of assertions is encouraged to enforce (1).
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#ifndef STORAGE_LEVELDB_DB_TABLE_H_
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#define STORAGE_LEVELDB_DB_TABLE_H_
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#include <memory>
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namespace leveldb {
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class MemTableRep {
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public:
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// KeyComparator(a, b) returns a negative value if a is less than b, 0 if they
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// are equal, and a positive value if b is greater than a
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class KeyComparator {
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public:
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virtual int operator()(const char* a, const char* b) const = 0;
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virtual ~KeyComparator() { }
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};
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// Insert key into the collection. (The caller will pack key and value into a
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// single buffer and pass that in as the parameter to Insert)
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// REQUIRES: nothing that compares equal to key is currently in the
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// collection.
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virtual void Insert(const char* key) = 0;
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// Returns true iff an entry that compares equal to key is in the collection.
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virtual bool Contains(const char* key) const = 0;
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// Returns an estimate of the number of bytes of data in use by this
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// data structure.
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virtual size_t ApproximateMemoryUsage() = 0;
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virtual ~MemTableRep() { }
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// Iteration over the contents of a skip collection
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class Iterator {
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public:
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// Initialize an iterator over the specified collection.
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// The returned iterator is not valid.
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// explicit Iterator(const MemTableRep* collection);
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virtual ~Iterator() { };
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// Returns true iff the iterator is positioned at a valid node.
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virtual bool Valid() const = 0;
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// Returns the key at the current position.
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// REQUIRES: Valid()
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virtual const char* key() const = 0;
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// Advances to the next position.
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// REQUIRES: Valid()
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virtual void Next() = 0;
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// Advances to the previous position.
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// REQUIRES: Valid()
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virtual void Prev() = 0;
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// Advance to the first entry with a key >= target
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virtual void Seek(const char* target) = 0;
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// Position at the first entry in collection.
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// Final state of iterator is Valid() iff collection is not empty.
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virtual void SeekToFirst() = 0;
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// Position at the last entry in collection.
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// Final state of iterator is Valid() iff collection is not empty.
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virtual void SeekToLast() = 0;
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};
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virtual std::shared_ptr<Iterator> GetIterator() = 0;
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};
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class MemTableRepFactory {
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public:
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virtual ~MemTableRepFactory() { };
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virtual std::shared_ptr<MemTableRep> CreateMemTableRep(
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MemTableRep::KeyComparator&) = 0;
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};
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}
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#endif // STORAGE_LEVELDB_DB_TABLE_H_
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