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rocksdb/db/merge_helper.h

65 lines
2.1 KiB

#ifndef MERGE_HELPER_H
#define MERGE_HELPER_H
#include "db/dbformat.h"
#include "leveldb/slice.h"
#include <string>
namespace leveldb {
class Comparator;
class Iterator;
class Logger;
class MergeOperator;
class MergeHelper {
public:
MergeHelper(const Comparator* user_comparator,
const MergeOperator* user_merge_operator,
Logger* logger,
bool assert_valid_internal_key)
: user_comparator_(user_comparator),
user_merge_operator_(user_merge_operator),
logger_(logger),
assert_valid_internal_key_(assert_valid_internal_key) {}
// Merge entries until we hit
// - a corrupted key
// - a Put/Delete,
// - a different user key,
// - a specific sequence number (snapshot boundary),
// or - the end of iteration
// iter: (IN) points to the first merge type entry
// (OUT) points to the first entry not included in the merge process
// stop_before: (IN) a sequence number that merge should not cross.
// 0 means no restriction
// at_bottom: (IN) true if the iterator covers the bottem level, which means
// we could reach the start of the history of this user key.
void MergeUntil(Iterator* iter, SequenceNumber stop_before = 0,
bool at_bottom = false);
// Query the merge result
// These are valid until the next MergeUtil call
// IMPORTANT: the key type could change after the MergeUntil call.
// Put/Delete + Merge + ... + Merge => Put
// Merge + ... + Merge => Merge
Slice key() { return Slice(key_); }
Slice value() { return Slice(value_); }
private:
const Comparator* user_comparator_;
const MergeOperator* user_merge_operator_;
Logger* logger_;
Iterator* iter_; // in: the internal iterator, positioned at the first merge entry
bool assert_valid_internal_key_; // enforce no internal key corruption?
// the scratch area that holds the result of MergeUntil
// valid up to the next MergeUntil call
std::string key_;
std::string value_;
};
} // namespace leveldb
#endif