Magnus Hagander wrote:
On Wed, Jun 13, 2007 at 02:02:24PM +0100, Heikki Linnakangas wrote:
DB2 has the concept of "explain tables". Explain output is written to tables, which tools query and pretty print the output. I like that idea in principle. PostgreSQL is a relational database, so having the explain output in relations make sense. No need for XML or any other extra libraries, in either the server or client. Having the data in relational format allows you to query them. For example, show me all sequential scans, or all nodes where the estimated number of rows is off by a certain factor.

Assuming you can actually *represent* the whole plan as tables, that would
of course work fine.

Sure you can. It's just a question of how complex the schema is :).

But I assume you mean "virtual tables"? So I do
EXPLAIN whatever, and get back one or more resultssets with the data? Or do
they write it to *actual* tables in the database?

I'm not sure. DB2 had real tables, but I found that a bit clumsy. It was nice because your old explain results were accumulated, but it was also not nice because of that same thing.

One idea would be temporary tables.

Machine-readable is of course the main point - the exact format is more of
an implementation detail.


A potential problem is that as we add new node types etc., we need to extend the schema (whether it's a real relational schema or XML), and clients need to understand it. But I guess we already have the same problem with clients that parse the current explain output.

  Heikki Linnakangas

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