Thread: performance of foreign key constraints
I have a table that has about 20 foreign key constraints on it. I think this is a bit excessive and am considering removing them ( they are all related to the same table and I don't think there is much chance of any integrity violations ). Would this improve performance or not? thanks
On Thu, Aug 28, 2003 at 06:15:57PM +0100, teknokrat wrote:
> I have a table that has about 20 foreign key constraints on it. I think
> this is a bit excessive and am considering removing them ( they are all
> related to the same table and I don't think there is much chance of any
> integrity violations ). Would this improve performance or not?
Almost certainly. But there's probably room for some middle ground
between 20 and none.
A
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On Thu, 28 Aug 2003, teknokrat wrote: > I have a table that has about 20 foreign key constraints on it. I think > this is a bit excessive and am considering removing them ( they are all > related to the same table and I don't think there is much chance of any > integrity violations ). Would this improve performance or not? It depends on your frequency of inserts/updates to the table with the constraint and the frequency of update/delete to the table(s) being refered to. My guess is probably. You may wish to leave some of the constraints (decide which are the most important), but 20 does seem a bit excessive in general.
Stephan Szabo wrote: > On Thu, 28 Aug 2003, teknokrat wrote: > > >>I have a table that has about 20 foreign key constraints on it. I think >>this is a bit excessive and am considering removing them ( they are all >>related to the same table and I don't think there is much chance of any >>integrity violations ). Would this improve performance or not? > > > It depends on your frequency of inserts/updates to the table with the > constraint and the frequency of update/delete to the table(s) being > refered to. My guess is probably. You may wish to leave some of the > constraints (decide which are the most important), but 20 does seem a bit > excessive in general. > The references are all to the same table i.e. they are employee ids, so leaving some and not others would make no sense. The table has no deletes, small amount of inserts and moderate amount of updates. However there are many selects and its their performance I am most concerned with. thanks
On Thu, 28 Aug 2003, teknokrat wrote: > Stephan Szabo wrote: > > > On Thu, 28 Aug 2003, teknokrat wrote: > > > > > >>I have a table that has about 20 foreign key constraints on it. I think > >>this is a bit excessive and am considering removing them ( they are all > >>related to the same table and I don't think there is much chance of any > >>integrity violations ). Would this improve performance or not? > > > > > > It depends on your frequency of inserts/updates to the table with the > > constraint and the frequency of update/delete to the table(s) being > > refered to. My guess is probably. You may wish to leave some of the > > constraints (decide which are the most important), but 20 does seem a bit > > excessive in general. > > > > The references are all to the same table i.e. they are employee ids, so > leaving some and not others would make no sense. The table has no > deletes, small amount of inserts and moderate amount of updates. However > there are many selects and its their performance I am most concerned with. The foreign keys should only really affect insert/update/delete performance. If you're using 7.3.4 (I think) then updates to the fk table that don't change any of the keys should be relatively cheap. I'd be much more worried if you had any changes the the referenced employee table that might change the key because that could get relatively expensive.
> The references are all to the same table i.e. they are employee ids, so > leaving some and not others would make no sense. The table has no > deletes, small amount of inserts and moderate amount of updates. However > there are many selects and its their performance I am most concerned with. Foreign keys have no impact on selects. Although this does sound like a rather strange design to me (20+ columns wide and they're all employee ids?)
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Rod Taylor wrote: >>The references are all to the same table i.e. they are employee ids, so >>leaving some and not others would make no sense. The table has no >>deletes, small amount of inserts and moderate amount of updates. However >>there are many selects and its their performance I am most concerned with. > > > Foreign keys have no impact on selects. > > Although this does sound like a rather strange design to me (20+ columns > wide and they're all employee ids?) There are more than 20 fieldss. Its a report that can get updated by different employees and we wish to keep a record of which employee completed which section. Couldn't think of any other way to do it.