Improving MySQL by Replicating to the In-Memory Database Tarantool

Replicating MySQL is one of the in-memory-database Tarantool’s killer functions. It allows you to keep your existing MySQL database while at the same time accelerating it and scaling it out horizontally. Even if you aren’t interested in extensive expansion, simply replacing existing replicas with Tarantool can save you money, because Tarantool is more efficient per core than MySQL. To read a testimonial of a company that implemented Tarantool replication on a large scale, please see here, as well as here.

I wanted to point out at the outset that if you run into any trouble with regards to the basics of Tarantool, you may wish to consult the first two tutorials in the Tarantool 101 series, which can be found here and here.

And please note that these instructions are for CentOS 7.5 and MySQL 5.7. They also assume that you have systemd installed and are working with an existing MySQL installation. Finally, a helpful log for troubleshooting during this tutorial is replicatord.log in /var/log. You can also have a look at the instance’s log example.log in /var/log/tarantool.

So let’s proceed.

First we’ll install the necessary packages in CentOS:

 yum -y install git ncurses-devel cmake gcc-c++ boost boost-  
 devel wget unzip nano bzip2 mysql-devel mysql-lib

Next we’ll clone the Tarantool-MySQL replication package from GitHub:

 git clone https://github.com/tarantool/mysql-tarantool-  
 replication.git

Now we can build the replicator with cmake:

 cd mysql-tarantool-replication
 git submodule update --init --recursive
 cmake .
 make

Our replicator will run as a systemd daemon called replicatord, so let’s edit its systemd service file, replicatord.service, in the mysql-tarantool-replication repo.
```
 nano replicatord.service 
```
Change the following line:
```
 ExecStart=/usr/local/sbin/replicatord -c /usr/local/etc/replicatord.cfg 
```
It should read:
```
 ExecStart=/usr/local/sbin/replicatord -c /usr/local/etc/replicatord.yml 
```

Next let’s copy some files from our replicatord repo to other necessary locations:

 cp replicatord /usr/local/sbin/replicatord
 cp replicatord.service /etc/systemd/system

Now let’s enter the MySQL console and create a sample database (depending on your existing installation, you may of course be a user other than root):
```
 mysql -u root -p
 CREATE DATABASE menagerie;
 QUIT 
```

Next we’ll get some sample data from MySQL, which we’ll pull into our root directory, then install from the terminal:

 cd
 wget https://downloads.mysql.com/docs/menagerie-db.zip
 unzip menagerie-db.zip
 cd menagerie-db
 mysql -u root -p menagerie < cr_pet_tbl.sql
 mysql -u root -p  menagerie < load_pet_tbl.sql
 mysql menagerie -u root -p < ins_puff_rec.sql
 mysql menagerie -u root -p < cr_event_tbl.sql

Let’s enter the MySQL console now and massage the data for use with the Tarantool replicator (we are adding an ID, changing a field name to avoid conflict, and cutting down the number of fields; note that with real data, this is the step that will involve the most tweaking):
```
 mysql -u root -p
 USE menagerie;
 ALTER TABLE pet ADD id INT PRIMARY KEY AUTO_INCREMENT FIRST;
 ALTER TABLE pet CHANGE COLUMN `name` `name2` VARCHAR(255);
 ALTER TABLE pet DROP sex, DROP birth, DROP death;
 QUIT 
```
Now that we have the sample data set up, we’ll need to edit MySQL’s configuration file for use with the replicator. Everything will go directly under [mysqld] in the file. (Note that your my.cnf for MySQL could be in a slightly different location.)
```
 cd nano /etc/my.cnf 
```
Set:
```
 binlog_format = ROW server_id = 1 log-bin=mysql-bin  
 interactive_timeout=3600 wait_timeout=3600   
 max_allowed_packet=32M 
```
After exiting nano, we’ll restart mysqld:
```
 systemctl restart mysqld 
```
Next, let’s install Tarantool and set up spaces for replication. Copy the entire script at https://www.tarantool.io/en/download/os-installation/1.10/rhel-centos-6-7/ and paste it into your terminal. You may have to press enter for the last line ( yum -y install tarantool ).
Now, we’ll write out a basic Tarantool program by editing the Lua example that ships with Tarantool:
```
 cd
 nano /etc/tarantool/instances.available/example.lua 
```

Replace the entire contents of the file with the following:

 box.cfg {
     listen = 3301;
     memtx_memory = 128 * 1024 * 1024; -- 128Mb
     memtx_min_tuple_size = 16;
     memtx_max_tuple_size = 128 * 1024 * 1024; -- 128Mb
     vinyl_memory = 128 * 1024 * 1024; -- 128Mb
     vinyl_cache = 128 * 1024 * 1024; -- 128Mb
     vinyl_max_tuple_size = 128 * 1024 * 1024; -- 128Mb
     vinyl_write_threads = 2;
     wal_mode = "none";
     wal_max_size = 256 * 1024 * 1024;
     checkpoint_interval = 60 * 60; -- one hou
r     checkpoint_count = 6;
     force_recovery = true;
 
     -- 1  “ SYSERROR
     -- 2  “ ERROR
     -- 3  “ CRITICAL
     -- 4  “ WARNING
     -- 5  “ INFO
     -- 6  “ VERBOSE
     -- 7  “ DEBUG
     log_level = 7;
     log_nonblock = true;
     too_long_threshold = 0.5;
 }
 
 box.schema.user.grant('guest','read,write,execute','universe')
 
 local function bootstrap()
 
     if not box.space.mysqldaemon then
         s = box.schema.space.create('mysqldaemon')
         s:create_index('primary',
         {type = 'tree', parts = {1, 'unsigned'}})
     end
 
     if not box.space.mysqldata then
         t = box.schema.space.create('mysqldata')
         t:create_index('primary',
         {type = 'tree', parts = {1, 'unsigned'}})
     end
 
 end
 
 bootstrap()

To understand more of what’s happening here, it would be best to have a look back at the earlier articles in our Tarantool 101 series.

Now we need to create a symlink from instances.available to a directory named instances.enabled (similar to NGINX). So in /etc/tarantool run the following:

 mkdir instances.enabled
 ln -s /instances.available/example.lua instances.enabled

Next we can start up our Lua program with tarantoolctl, a wrapper for systemd:
```
 tarantoolctl start example.lua 
```
Now let’s enter our Tarantool instance, where we can check that our target spaces were successfully created:
```
 tarantoolctl enter example.lua box.space._space:select() 
```
You should see the mysqldaemon and mysqldata spaces at the very bottom. Exit with CTRL-C .

Now that we have MySQL and Tarantool set up, we can proceed to configure our replicator. First let’s work with replicator.yml in the main tarantool-mysql-replication directory.

 nano replicatord.yml

Change the entire file as follows, making sure to add your MySQL password and to set the appropriate user:

 mysql:     host: 127.0.0.1
     port: 3306
     user: root
     password: <your MySQL password>
     connect_retry: 15 # seconds
 
 tarantool:
     host: 127.0.0.1:3301
     binlog_pos_space: 512
     binlog_pos_key: 0
     connect_retry: 15 # seconds
     sync_retry: 1000 # milliseconds
 
 mappings:
     - database: menagerie
     table: pet
     columns: [ id, name2, owner, species]
     space: 513
     key_fields:  [0]
     # insert_call: function_name
     # update_call: function_name
     # delete_call: function_name

Now we need to copy replicatord.yml to the location where systemd looks for it:
```
 cp replicatord.yml /usr/local/etc/replicatord.yml 
```
Next we can start up the replicator:
```
 systemctl start replicatord 
```

Now we can enter our Tarantool instance and do a select on the mysqldata space. We will see the replicated content from MySQL:

 tarantoolctl enter example.lua
 box.space.mysqldata:select()

The results will be:

 - - [1, 'Fluffy', 'Harold', 'cat']
   - [2, 'Claws', 'Gwen', 'cat']
   - [3, 'Buffy', 'Harold', 'dog']
   - [4, 'Fang', 'Benny', 'dog']
   - [5, 'Bowser', 'Diane', 'dog']
   - [6, 'Chirpy', 'Gwen', 'bird']
   - [7, 'Whistler', 'Gwen', 'bird']
   - [8, 'Slim', 'Benny', 'snake']
   - [9, 'Puffball', 'Diane', 'hamster']

Finally let’s enter a record into MySQL and then go back to Tarantool to make sure it’s replicated. So first we’ll exit our Tarantool instance:
```
 CTRL-C 
```
Then:
```
 mysql -u root -p
 USE menagerie;
 INSERT INTO pet(name2, owner, species) VALUES ( Spot',  Brad',  dog');
 QUIT 
```
(Note that for the insert statement above, you may need to change the quotes to straight quotes if you are having issues.)
Once back in the terminal enter:
```
 tarantoolctl enter example.lua
 box.space.mysqldata:select() 
```
You should see the replicated data in Tarantool!