What does "waiting for handler commit" mean in relation to the slow writes experienced in MySQL 8?

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"Waiting for handler commit" is a message that appears in the MySQL error log when the storage engine is waiting for a transaction commit to be completed by the handler. It appears in relation to slow writes because if the transaction commit takes too long, it can result in slow queries and slow server response times. This can be caused by several factors such as large transactions, inefficient storage engine configuration or insufficient system resources. It is important to address this issue in order to improve the performance and scalability of the MySQL database.