如何使用大量数据迁移 MySQL？

Question

So I want a service to start using a new MySQL instance like nothing happened. I just want to change the DB URL and credentials and have my service working like it was working.

The problem is that we want to minimize the downtime.

How if my database has 30GB of data?

One of our solutions is:

• Create a new instance as if it's a follower
• Make sure the new instance is fully synchronized
• Make service point to the new DB
• Make new instance independent

We are just not sure how to make sure it's fully synchronized and if the new instance can become independent after it was a follower.

How to make sure it's fully synchronized and how to make it independent?

Answer 1

First you initialize the replica with a snapshot from the master. There are instructions here: https://dev.mysql.com/doc/refman/5.7/en/replication-howto.html

To make sure it's synchronized before you cut over:

1. Halt changes on the primary. A good way to do this is to set global read_only=1;
2. View the binary log position on the primary: show master status\G After you enable read_only there shouldn't be any new changes, so the binary log will stop growing (note users with SUPER privilege can still write changes, so you might need to prevent this with set global super_read_only=1; too).
3. View the binary log position on the replica: show slave status\G When Master_Log_File and Exec_Master_Log_Pos catch up to the values you observed on the primary, then it's caught up.
4. Change the application to connect directly to the replica and resume reading and writing queries.
5. Tell the replica to forget its replication subscription: reset slave;
6. Now the former primary is redundant, and it will only take moments of application traffic before the new primary (former replica) has new data that the old instance doesn't have.

I recommend that you practice this a few times in a test environment before attempting it on your real system. Once you are familiar with the steps, it should be possible to do it pretty quickly. I would be confident of doing it in less than one minute of downtime.