On Wed, 2007-03-07 at 21:27 -0700, Jim Nasby wrote:
> On Mar 7, 2007, at 3:26 AM, Simon Riggs wrote:
> > If you know that the constraints on each of the tables is distinct,
> > then
> > building a UNIQUE index on each of the partitions is sufficient to
> > prove
> > that all rows in the combined partitioned table are distinct also.
> >
> > The hard part there is checking that the partition constraints are
> > distinct. If the partition constraints are added one at a time, you
> > can
> > use the predicate testing logic to compare the to-be-added partition's
> > constraint against each of the already added constraints. That becomes
> > an O(N) problem.
> >
> > What is really needed is a data structure that allows range partitions
> > to be accessed more efficiently. This could make adding partitions and
> > deciding in which partition a specific value goes an O(logN)
> > operation.
>
> Directing data to child tables with triggers pretty much necessitates
> having some way to codify what partition a particular row belongs in.
> IE: for partitioning by month, you'll see things like naming the
> partition tables "parent_table_name_$YEAR_$MONTH", so the
> 'partitioning function' takes a date or timestamp and then returns
> what partition it belongs to. Perhaps there is some way to use that
> mapping to drive the selection of what partitions could contain a
> given value?
>
> One possibility would be to require 3 functions for a partitioned
> table: one accepts the partitioning key and tells you what partition
> it's in, one that tells you what the minimum partitioning key for a
> partition would be, and one that tells you what the maximum would be.
> If the user supplied those 3 functions, I think it would be possibly
> to automatically generate code for the triggers and check
> constraints. The min/max partition key functions might allow you to
> more efficiently do partition elimination, too.
ISTM this is a good idea.
SQLServer uses partitioning functions and I like that approach. It makes
it much easier to do partition-wise joins between tables that share
partitioning functions.
-- Simon Riggs EnterpriseDB http://www.enterprisedb.com
