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rocksdb/utilities/merge_operators/string_append/stringappend.cc

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/**
* A MergeOperator for rocksdb/leveldb that implements string append.
* @author Deon Nicholas (dnicholas@fb.com)
* Copyright 2013 Facebook
*/
#include "stringappend.h"
#include <memory>
#include <assert.h>
#include "rocksdb/slice.h"
#include "rocksdb/merge_operator.h"
#include "utilities/merge_operators.h"
namespace rocksdb {
// Constructor: also specify the delimiter character.
StringAppendOperator::StringAppendOperator(char delim_char)
: delim_(delim_char) {
}
// Implementation for the merge operation (concatenates two strings)
bool StringAppendOperator::Merge(const Slice& key,
const Slice* existing_value,
const Slice& value,
std::string* new_value,
Logger* logger) const {
// Clear the *new_value for writing.
assert(new_value);
new_value->clear();
if (!existing_value) {
// No existing_value. Set *new_value = value
new_value->assign(value.data(),value.size());
} else {
// Generic append (existing_value != null).
// Reserve *new_value to correct size, and apply concatenation.
new_value->reserve(existing_value->size() + 1 + value.size());
new_value->assign(existing_value->data(),existing_value->size());
new_value->append(1,delim_);
new_value->append(value.data(), value.size());
}
return true;
}
const char* StringAppendOperator::Name() const {
return "StringAppendOperator";
}
std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator() {
return std::make_shared<StringAppendOperator>(',');
}
} // namespace rocksdb