Do you know MySQL has Blackhole?

The MySQL Blackhole storage engine is a unique engine that does not store any data. Instead, it discards any data that is inserted into it and always returns an empty result set for SELECT queries. So why would anyone use it?

The Blackhole engine can be useful in a few specific situations. For example, you might use it to capture and discard slow query log data, or to route certain types of queries to a separate server or application. It can also be used as a placeholder for a real storage engine, or as a way to “blackhole” or discard certain types of data.

However, it’s important to note that the Blackhole engine is not a general-purpose storage engine and should not be used as the primary storage engine for your data. It is designed for specific use cases where data does not need to be stored, and its limited functionality makes it unsuitable for most applications.

Creating a Blackhole-Engine Table

To use the Blackhole engine, you must create a Blackhole engine table in your MySQL database. You can do this using the CREATE TABLE statement, with the ENGINE option set to BLACKHOLE:

mysql> CREATE TABLE test(i INT, c CHAR(10)) ENGINE = BLACKHOLE;
--Query OK, 0 rows affected (0.03 sec)
 
will save the data, but it will thorw it to BLACKHOLE
mysql> INSERT INTO test VALUES(1,'record one'),(2,'record two');
--Query OK, 2 rows affected (0.00 sec)
--Records: 2  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM test;
--Empty set (0.00 sec)

Once you have created a Blackhole-engine table, you can use it just like any other table in MySQL. However, any data you insert into it will be discarded, and SELECT queries will always return an empty result set.

Use Cases for the Blackhole Engine

Here are a few potential use cases for the MySQL Blackhole storage engine:

1. Discarding slow query log data: You can configure the MySQL server to log all queries that take a long time to execute to a Blackhole-engine table, which will discard the data after it is written. This can be useful for tracking slow queries without filling up your disk space with logs.
2. Routing certain types of queries to a separate server: You can create a Blackhole-engine table that has the same structure as a table on a different server, and then use MySQL’s federated tables feature to route queries to the Blackhole table to the other server. This can be used to distribute the workload of certain types of queries across multiple servers.
3. Testing MySQL server configurations: You can use the Blackhole engine to test how the MySQL server handles different storage engines and configurations, without the need to actually store any data.
4. Discarding unwanted data: In some cases, you may want to discard certain types of data that are being logged or stored in a database. For example, you might use the Blackhole engine to discard spam or invalid data that is being logged by an application.
5. Capturing data for external processing: In some cases, you may want to capture data that is being written to a database table, but you may not want to actually store the data in the database. For example, you might have an application that generates a large amount of log data, and you want to process the data in real-time without storing it in the database. In this case, you can use the Blackhole engine to capture the data as it is written to the database, and then process it using an external application or script. This can be an efficient way to handle large volumes of data without overloading the database.

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