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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. | |
19 | StringAppendOperator::StringAppendOperator(char delim_char) | |
20 | : delim_(delim_char) { | |
21 | } | |
22 | ||
23 | // Implementation for the merge operation (concatenates two strings) | |
24 | bool StringAppendOperator::Merge(const Slice& key, | |
25 | const Slice* existing_value, | |
26 | const Slice& value, | |
27 | std::string* new_value, | |
28 | Logger* logger) const { | |
29 | ||
30 | // Clear the *new_value for writing. | |
31 | assert(new_value); | |
32 | new_value->clear(); | |
33 | ||
34 | if (!existing_value) { | |
35 | // No existing_value. Set *new_value = value | |
36 | new_value->assign(value.data(),value.size()); | |
37 | } else { | |
38 | // Generic append (existing_value != null). | |
39 | // Reserve *new_value to correct size, and apply concatenation. | |
40 | new_value->reserve(existing_value->size() + 1 + value.size()); | |
41 | new_value->assign(existing_value->data(),existing_value->size()); | |
42 | new_value->append(1,delim_); | |
43 | new_value->append(value.data(), value.size()); | |
44 | } | |
45 | ||
46 | return true; | |
47 | } | |
48 | ||
49 | const char* StringAppendOperator::Name() const { | |
50 | return "StringAppendOperator"; | |
51 | } | |
52 | ||
53 | std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator() { | |
54 | return std::make_shared<StringAppendOperator>(','); | |
55 | } | |
56 | ||
57 | } // namespace rocksdb |