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I have a MySql Db with innoDB tables.
I need to alter a couple of big tables (~50M records), since altering locks the tables I want to make the process as fast as possible.
What is best in term of speed:
1. altering one table at a time
2. alter both tables on the same time (simultaneously)
any ideas?
Really depends on how much memory you have in your server.
When you’re doing ALTER TABLE, you really want the table and its largest secondary index (remember innodb clusters the primary key, so PK is stored with the rows) to fit into memory. If it doesn’t, it’s going to be slow (NB: This discussion assumes the table is not partitioned).
As your table has a tiny 50M rows, the chances are it fits in RAM trivially (you have 32G+ on your server, right?) with all its secondary indexes.
If it all fits in the innodb buffer pool, do them in parallel. If it doesn’t do them in series.
Try it on your development server which has the same spec as production (obviously configure them with the same size innodb_buffer_pool)