store TEXT/BLOB in same table or not?

Question

While searching trough SO, I\'ve found two contradicting answers (and even a comment that stated that) but no definitive answer:

The problem is: is there any perform

Answer 1

One performance gain is to have a table with fixed length records. This would mean no variable length fields like varchar or text/blob. With fixed length records, MySQL doesn't need to "seek" the end of a record since it knows the size offset. It also knows how much memory it needs to load X records. Tables with fixed length records are less prone to fragmentation since space made available from deleted records can be fully reused. MyISAM tables actually have a few other benefits from fixed length records.

Assuming you are using innodb_file_per_table, keeping the tex/blob in a separate table will increase the likelihood that the file system caching will be used since the table will be smaller.

That said, this is a micro optimization. There are many other things you can do to get much bigger performance gains. For example, use SSD drives. It's not going to give you enough of a performance boost to push out the day of reckoning when your tables get so big you'll have to implement sharding.

You don't hear about databases using the "raw file system" anymore even though it can be much faster. "Raw" is when the database accesses the disk hardware directly, bypassing any file system. I think Oracle still supports this. But it's just not worth the added complexity, and you have to really know what you are doing. In my opinion, storing your text/blob in a separate table just isn't worth the added complexity for the possible performance gain. You really need to know what you are doing, and your access patterns, to take advantage of it.