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Version: v7 - alpha

FAQ & Troubleshooting

Working with an existing database​

Sequelize works best when it handles the creation of your database tables for you. Many options are automatically configured for you to ease the development process.

Sometimes, however, you may need to work with an existing database, and Sequelize must adapt to you, not the other way around. To do this, you will need to let Sequelize know about your existing tables and how they are structured.

The following pages will teach you how to do this:

Error: Can't create more than max_prepared_stmt_count statements (MySQL)​

If you're using MySQL and encounter this error, it means that Sequelize is creating more prepared statements than your MySQL server allows.

To fix this, you need to configure the maxPreparedStatements option in your Sequelize constructor to a value that will not cause Sequelize to create more statements than the max_prepared_stmt_count value of your MySQL server.

const sequelize = new Sequelize({
  // ...
  dialectOptions: {
    maxPreparedStatements: 100,
  },
});

The max_prepared_stmt_count limit is a database-wide limit, and prepared statements are created per-connection. This means that the maxPreparedStatements option should be set to a value that is less than the max_prepared_stmt_count value divided by the number of concurrent connections to your database.

To figure out a good value for this option, you can do the following:

  1. Determine the value of max_prepared_stmt_count on your MySQL server: 
    SHOW VARIABLES LIKE 'max_prepared_stmt_count';
  2. Determine how many concurrent connections can be connected to your database at the same time. 
    SHOW VARIABLES LIKE 'max_connections';
  3. Set maxPreparedStatements to the result of FLOOR(max_prepared_stmt_count / max_connections).