完成MySQL转储的数据库重置？

Question

This may seem like a very dumb question but I didn't learn it in any other way and I just want to have some clarification.

I started to use MySQL a while ago and in order to test various scenarios, I back up my databases. I used MySQL dump for that:

Export:

mysqldump -hSERVER -uUSER -pPASSWORD --all-databases > filename.sql

Import:

mysql -hSERVER -uUSER -pPASSWORD < filename.sql

Easy enough and it worked quite well up until now, when I noticed a little problem with this "setup": It does not fully "reset" the databases and tables. If, for example, there is an additional table added AFTER a dump file has been created, that additional table will not disappear if you import the same dump file. It essentially only "corrects" tables already there and recreates any databaes or tables missing, but does not remove any additional tables, which happen to have names that are not in the dump file.

What I want to do is to completely reset all the databases on a server when I import such a dump file. What would be the best solution? Is there a special import function reserved for that purpose or do I have to delete the databases myself first? Or is that a bad idea?

Answer 1

You can use the parameter --add-drop-database to add a "drop database" statement to the dump before each "create database" statement.

eg

mysqldump -hSERVER -uUSER -pPASSWORD --all-databases --add-drop-database >filename.sql

see here for details.

Answer 2

There's nothing magic about the dump and restore processes you describe. mysqldump writes out SQL statements that describe the current state of the database or databases you are dumping. It has to fetch a list of tables in each database you're dumping, then it has to read the tables one by one and write them out as SQL. On databases of any size, this takes time.

So, if you create a new table while mysqldump is running, it may not pick up that new table. Similarly, if your application software changes contents of tables while mysqldump is running, those changes may or may not show up in the backup.

You can look at the .sql files mysqldump writes out to see what they have picked up. If you want to be sure that your dumped .sql files are perfect, you need to run mysqldump on a quiet server -- one where nobody is running data definition language.

MySQL hot backup solutions are available. You may need to look into that.

Answer 3

The OP may want look into

mysql_install_db

if they want a fresh start with the post-install default settings before restoring one or more dumped DBs. For production servers, another useful script is:

mysql_secure_installation

Also, they may prefer to dump the DB(s) they created separately:

mysqldump -hSERVER -uUSER -pPASSWORD --database foo > foo.sql

to avoid inadvertently changing the internal DBs: mysql, information_schema, performance_schema.