* Heikki Linnakangas (heikki.linnakan...@enterprisedb.com) wrote:
> 1. We probably don't want the SQL syntax to be added to the grammar.
> This should be written as an extension, using custom functions as
> the API, instead of extra SQL syntax.

Err, I missed that, and don't particularly agree with it..  Is there a
serious issue with the grammar defined in the SQL standard?  The other
DBs which provide this- do they use the SQL grammar or something else?

I'm not sure that I particularly *like* the SQL grammar, but if we're
going to implement this, we should really do it 'right'.

> 2. It's not very useful if it's just a dummy replacement for "WHERE
> random() < ?". It has to be more advanced than that. Quality of the
> sample is important, as is performance. There was also an
> interesting idea of on implementing monetary unit sampling.

In reviewing this, I got the impression (perhaps mistaken..), that
different sampling methods are defined by the SQL standard and that it
would simply be us to implement them according to what the standard

> I think this would be a useful project if those two points are taken
> care of.

Doing it 'right' certainly isn't going to be simply taking what Neil did
and updating it, and I understand Tom's concerns about having this be
more than a hack on seqscan, so I'm a bit nervous that this would turn
into something bigger than a GSoC project.

> Another idea that Robert Haas suggested was to add support doing a
> TID scan for a query like "WHERE ctid<  '(501,1)'". That's not
> enough work for GSoC project on its own, but could certainly be a
> part of it.

I don't think Robert's suggestion would be part of a 'tablesample'
patch.  Perhaps a completely different project which was geared towards
allowing hidden columns to be used in various ways in a WHERE clause..
Of course, we'd need someone to actually define that; I don't think
someone relatively new to the project is going to know what experienced
hackers want to do with system columns.



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