1 /**
2 * A MergeOperator for rocksdb that implements string append.
3 * @author Deon Nicholas (dnicholas@fb.com)
4 * Copyright 2013 Facebook
5 */
6
7 #include "stringappend.h"
8
9 #include <memory>
10 #include <assert.h>
11
12 #include "rocksdb/slice.h"
13 #include "rocksdb/merge_operator.h"
14 #include "utilities/merge_operators.h"
15
16 namespace rocksdb {
17
18 // Constructor: also specify the delimiter character.
StringAppendOperator(char delim_char)19 StringAppendOperator::StringAppendOperator(char delim_char)
20 : delim_(delim_char) {
21 }
22
23 // Implementation for the merge operation (concatenates two strings)
Merge(const Slice &,const Slice * existing_value,const Slice & value,std::string * new_value,Logger *) const24 bool StringAppendOperator::Merge(const Slice& /*key*/,
25 const Slice* existing_value,
26 const Slice& value, std::string* new_value,
27 Logger* /*logger*/) const {
28 // Clear the *new_value for writing.
29 assert(new_value);
30 new_value->clear();
31
32 if (!existing_value) {
33 // No existing_value. Set *new_value = value
34 new_value->assign(value.data(),value.size());
35 } else {
36 // Generic append (existing_value != null).
37 // Reserve *new_value to correct size, and apply concatenation.
38 new_value->reserve(existing_value->size() + 1 + value.size());
39 new_value->assign(existing_value->data(),existing_value->size());
40 new_value->append(1,delim_);
41 new_value->append(value.data(), value.size());
42 }
43
44 return true;
45 }
46
Name() const47 const char* StringAppendOperator::Name() const {
48 return "StringAppendOperator";
49 }
50
CreateStringAppendOperator()51 std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator() {
52 return std::make_shared<StringAppendOperator>(',');
53 }
54
CreateStringAppendOperator(char delim_char)55 std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator(char delim_char) {
56 return std::make_shared<StringAppendOperator>(delim_char);
57 }
58
59 } // namespace rocksdb
60