On Nov 3, 2005, at 10:21 AM, Merlin Moncure wrote:
Reading the previous paragraphs I was just about to suggest this. This
is a much more elegant method...you are reaping the benefits of having
normalized your working set. You were trying to denormalize it back to
what you were used to.  Yes, now you can drop your index and simplify
your queries...normalized data is always more 'natural'.

I'm not sure normalized is the right word. In either case, I'm storing it in the same form. In either case, my ConcurrencyProcessor class gets the same form. The only difference is if the database splits the rows or if my application does so.

But we're essentially agreed. This is the algorithm I'm going to try implementing, and I think it will work out well. It also means sending about half as much data from the database to the application.

Mind you, I still think PostgreSQL should be able to perform that
sorted union fast. Maybe sometime I'll have enough free time to take
my first plunge into looking at a database query planner.

I'm not so sure I agree, by using union you were basically pulling two
independent sets (even if they were from the same table) that needed to
be ordered.


  There is zero chance of using the index here for ordering
because you are ordering a different set than the one being indexed.

I don't think that's true. It just needs to look at the idea of independently ordering each element of the union and then merging that, compared to the cost of grabbing the union and then ordering it. In this case, the former cost is about 0 - it already has independently ordered them, and the merge algorithm is trivial. <http://en.wikipedia.org/wiki/Merge_algorithm>


Scott Lamb <http://www.slamb.org/>

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