On Mon, Mar 07, 2011 at 11:43:20AM -0500, Tom Lane wrote: > Is there any documentation of $SUBJECT? Because the more I look at > this patch the more I think it's misdesigned; either that or I > fundamentally misunderstand what it's trying to do. I complained > yesterday about why the planner wasn't using indcollation to identify > the sort order of an index. I now think that the reason it doesn't > obviously fail to fail is that indcollation is dead code, and so is > approximately 99% of what you added to the planner, because two > expressions that are equal() must necessarily have the same collation > property. Tracking the collation as a separate property of a pathkey > is thus a useless activity. If this conclusion isn't correct, please > explain why not.
The collation is a property of the operators/functions and not of the values. An individual value does not have a collation, a column does. A pathkey represents a sort order, right? To define a sort order you need a collation and so the path key is the natural place to put it. Two path keys that differ only by the collation are *not* compatable, but obviously can be converted by a sort node. After the plan phase, the collation will be ignored in 99% of the executer, except for operators like =, < and > that need to look at it. Have a nice day, -- Martijn van Oosterhout <klep...@svana.org> http://svana.org/kleptog/ > Patriotism is when love of your own people comes first; nationalism, > when hate for people other than your own comes first. > - Charles de Gaulle
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