When is a query too big?

I'm monitoring calls and putting them into 开发者_如何学Pythona database. I'm putting caller, called, start, end in database. There are an average of 70-80 calls a day (none in the weekend), so it comes to 350-400 a week. The program will be used for a long time, so after a year there will be many items in the database.

A part of the program shows the calls in a graph (volume / day) and also in listbox (who called who). For that I'm using a typical "select * from table" to retrieve the info.

When will the query be so big that the user will experience performance loss?

Update:

I need all the info from the table, so a select * was best to use according to some people.

Each row in the database contains 1 int and 4 strings, simple data.

Put a limit on it now.

Do you really need the data for all time? What's reasonable for the graph/list? 30 days? 60 days? User-selectable?

Though, 20000 calls a year is not a huge data volume.

Also, bad form to SELECT * -- you should always specify the column list you're selecting.

You didn't specify what your data store is, schema, indexes, etc. So there is very little information to go on.

But, as a general rule (tongue firmly in cheek):

When the users start complaining.

There should never be a performance problem during the life of the application, even if your volume increases. As long as:

• you have good indexes on the fields your queries use.
• you don't do something really silly in your queries.

Without good indexes, you will eventually have problems. A couple less important bits of advice:

• specify the columns you want, rather than using "Select *"
• make sure you're reporting query isn't being called a thousand times a second or something crazy like that.

If you're only doing a simple select, then I'm guessing millions of records before someone will notice.

Of course, if you're db server is on a slow machine, that will also hinder it.

Are you doing any Where clauses or Grouping? Any Joins? If so, are those on Indexed columns?

The best answer would be: It Depends.

How long is a piece of string?

This depends on so many factors (including what you deem to be a 'performance loss') that it is impossible to give a firm answer here. You're going to have to test it yourself and see