ceph/src/rocksdb/utilities/merge_operators/string_append/stringappend.cc

   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