rocksdb/utilities/merge_operators/string_append/stringappend2.cc
Yueh-Hsuan Chiang cda4006e87 Enhance partial merge to support multiple arguments
Summary:
* PartialMerge api now takes a list of operands instead of two operands.
* Add min_pertial_merge_operands to Options, indicating the minimum
  number of operands to trigger partial merge.
* This diff is based on Schalk's previous diff (D14601), but it also
  includes necessary changes such as updating the pure C api for
  partial merge.

Test Plan:
* make check all
* develop tests for cases where partial merge takes more than two
  operands.

TODOs (from Schalk):
* Add test with min_partial_merge_operands > 2.
* Perform benchmarks to measure the performance improvements (can probably
  use results of task #2837810.)
* Add description of problem to doc/index.html.
* Change wiki pages to reflect the interface changes.

Reviewers: haobo, igor, vamsi

Reviewed By: haobo

CC: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D16815
2014-03-24 17:57:13 -07:00

114 lines
3.1 KiB
C++

/**
* @author Deon Nicholas (dnicholas@fb.com)
* Copyright 2013 Facebook
*/
#include "stringappend2.h"
#include <memory>
#include <string>
#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.
StringAppendTESTOperator::StringAppendTESTOperator(char delim_char)
: delim_(delim_char) {
}
// Implementation for the merge operation (concatenates two strings)
bool StringAppendTESTOperator::FullMerge(
const Slice& key,
const Slice* existing_value,
const std::deque<std::string>& operands,
std::string* new_value,
Logger* logger) const {
// Clear the *new_value for writing.
assert(new_value);
new_value->clear();
// Compute the space needed for the final result.
int numBytes = 0;
for(auto it = operands.begin(); it != operands.end(); ++it) {
numBytes += it->size() + 1; // Plus 1 for the delimiter
}
// Only print the delimiter after the first entry has been printed
bool printDelim = false;
// Prepend the *existing_value if one exists.
if (existing_value) {
new_value->reserve(numBytes + existing_value->size());
new_value->append(existing_value->data(), existing_value->size());
printDelim = true;
} else if (numBytes) {
new_value->reserve(numBytes-1); // Minus 1 since we have one less delimiter
}
// Concatenate the sequence of strings (and add a delimiter between each)
for(auto it = operands.begin(); it != operands.end(); ++it) {
if (printDelim) {
new_value->append(1,delim_);
}
new_value->append(*it);
printDelim = true;
}
return true;
}
bool StringAppendTESTOperator::PartialMergeMulti(
const Slice& key, const std::deque<Slice>& operand_list,
std::string* new_value, Logger* logger) const {
return false;
}
// A version of PartialMerge that actually performs "partial merging".
// Use this to simulate the exact behaviour of the StringAppendOperator.
bool StringAppendTESTOperator::_AssocPartialMergeMulti(
const Slice& key, const std::deque<Slice>& operand_list,
std::string* new_value, Logger* logger) const {
// Clear the *new_value for writing
assert(new_value);
new_value->clear();
assert(operand_list.size() >= 2);
// Generic append
// Determine and reserve correct size for *new_value.
size_t size = 0;
for (const auto& operand : operand_list) {
size += operand.size();
}
size += operand_list.size() - 1; // Delimiters
new_value->reserve(size);
// Apply concatenation
new_value->assign(operand_list.front().data(), operand_list.front().size());
for (std::deque<Slice>::const_iterator it = operand_list.begin() + 1;
it != operand_list.end(); ++it) {
new_value->append(1, delim_);
new_value->append(it->data(), it->size());
}
return true;
}
const char* StringAppendTESTOperator::Name() const {
return "StringAppendTESTOperator";
}
std::shared_ptr<MergeOperator>
MergeOperators::CreateStringAppendTESTOperator() {
return std::make_shared<StringAppendTESTOperator>(',');
}
} // namespace rocksdb