尝试向MYSQL表添加新列时失去连接

Question

I'm trying to add a column to a mysql table that has over 25 million rows. I am running the sql command

ALTER TABLE `table_name` ADD COLUMN `column_name` varchar(128) NULL DEFAULT NULL;

This is being run using the mysql command line application.

Every time i try to run this it takes hours and then i get the error

ERROR 2013 (HY000): Lost connection to MySQL server during query

The database is running in a RDS instance on AWS and checking the monitoring statistics neither the memory or disk space is being exhausted.

Is there anything else i can try to add this column to the table?

Answer 1

Check your memory usage or, more probably, your disk usage (is there enough free space during the process?). Altering a table may require either a large amount of memory or a copy on disk of your table. Changing the alter algorithm from INPLACE to COPY can be even faster in your particular case.

You may also be hitting the innodb_online_alter_log_max_size limit, although in that case, only the query should fail, not the entire server. It is possible that the crash may be happening due to the ROLLBACK , and not the operation itself, though.

Finally, some application configurations or hosting servers cancels a query/http request that is taking too long, I recommend you to execute the same query on the command line client for testing purposes.