Merge

Go to the /home directory.
```
cd /home/
```
Create the following source code:
```
vim rocksdb_test_merge.cpp
```

Add code content.

#include <iostream>
#include <vector>
#include <rocksdb/db.h>
#include <rocksdb/options.h>
#include <rocksdb/table.h>
#include <rocksdb/merge_operator.h>
#include <rocksdb/filter_policy.h>
#include <rocksdb/perf_context.h>
#include <rocksdb/iostats_context.h>
#include <rocksdb/trace_reader_writer.h>
#include "rocksdb/utilities/merge_operators.h"
using namespace rocksdb;
using namespace std;
int main()
{
  DB* db;
  Options options;
  options.create_if_missing = true;
  //no compression
  options.compression = kNoCompression;
  BlockBasedTableOptions table_options;
  table_options.no_block_cache = true;
  table_options.cache_index_and_filter_blocks = false;
  options.table_factory.reset(NewBlockBasedTableFactory(table_options));
  options.merge_operator = MergeOperators::CreateStringAppendOperator();
  Status s=rocksdb::DB:: Open(options,"/home/rocksdb/rkdb2",&db);
  if(!s.ok()){
cout<<"open rocksdb failed:"<<s.ToString()<<endl;
delete db;
    exit(-1);
  }
    cout<<"open rocksdb success!"<<endl;
  //Merge operator
  int j = 0;
  string key = to_string(j);
  string value;
  char buf[8];
//EncodeFixed64(buf,2);
  s = db->Merge(WriteOptions(),key,"1");
    //need change
  if(!s.ok()){
    cout << "Merge value failed:" << s.ToString()<<endl;
    delete db;
    exit(-1);
  }
  s = db->Merge(WriteOptions(),key,"2");
  db->Flush(FlushOptions());
  if(!s.ok()){
    cout << "Merge value failed:" << s.ToString()<<endl;
    delete db;
    exit(-1);
  }
 s = db->Get(ReadOptions(),key,&value);
  if(!s.ok()){
    cout << "Merge value failed:" << s.ToString()<<endl;
    delete db;
    exit(-1);
  }
  cout << "Get merge value: " << value << "\n value of size:" << value.size() << endl;
}

Create a database directory.
```
mkdir -p /home/rocksdb/rkdb2
```

Compile the code.

g++ -o rocksdb_test_merge --std=c++11 rocksdb_test_merge.cpp -lrocksdb -ldl

Run the executable file.
```
./rocksdb_test_merge
```

Query data in the database.

ldb --db=/home/rocksdb/rkdb2 scan

Parent topic: Verifying RocksDB APIs