Dynamically creating tables as a means of partitioning: OK or bad practice?

Question

Is it reasonable for an application to create database tables dynamically as a means of partitioning?

For example, say I have a large table "widgets" with a "userID" column identifying the owner of each row. If this table tended to grow extremely large, would it make sense to instead have the application create a new table called "widgets_{username}" for each new user? Assume that the application will only ever have to query for widgets belonging to a single user at a time (i.e. no need to try and join any of these user widget tables together).

Doing this would break up the one large table into more easily-managed chunks, but this doesn't seem like an elegant solution. In my mind, the database schema should be defined when the application is written, and any runtime data is stored as rows, not as additional tables.

As a more general question, is modifying the database schema at runtime ever ok?

Edit: This question is mostly hypothetical; I had a pretty good feeling that creating tables at runtime didn't make sense. That being said, we do have a table with millions of rows in our application. SELECTs perform fine, but things like deleting all rows owned by a particular user can take a while. Basically I'm looking for some solid reasoning why just dynamically creating a table for each user doesn't make sense for when I'm asked.

Answer 1

NO, NO, NO!! Now repeat after me, I will not do this because it will create many headaches and problems in the future! Databases are made to handle large amounts of information. they use indexes to quickly find what you are after. think phone book how effective is the index? would it be better to have a different book for each last name?

This will not give you anything performance wise. Keep a single table, but be sure to index on UserID and you'll be able to get the data fast. however if you split the table up, it becomes impossible/really really hard to get any info that spans multiple users, like search all users for a certain widget, count of all widgets of a certain type, etc. you need to have every query be built dynamically.

If deleting rows is slow, look into that. How many rows at one time are we talking about 10, 1000, 100000? What is your clustered index on this table? Could you use a "soft delete", where you have a status column that you UPDATE to "D" to mark the row as deleted. Can you delete the rows at a later time, with less database activity. is the delete slow because it is being blocked by other activity. look into those before you break up the table.