Re: Database slowness -- my design, hardware, or both?

Hi, Alvaro Herrera.  You wrote:

Don't assume -- measure.  I had a query which ran orders of magnitude
faster because I interpolated the constant list in the big query.  The
table from which the interpolated values were being extracted had about
30 rows or so. 

OK, I modified things to use interpolation.  Here's the updated query:

explain  UPDATE Transactions
               SET previous_value = previous_value(id)
             WHERE new_value IS NOT NULL
               AND new_value <> ''
               AND node_id IN (351, 169, 664, 240);

And here is the query plan produced by explain:

                                    QUERY PLAN                                   
----------------------------------------------------------------------------------
 Bitmap Heap Scan on transactions  (cost=8842.88..98283.93 rows=407288 width=249)
   Recheck Cond: (node_id = ANY ('{351,169,664,240}'::integer[]))
   Filter: ((new_value IS NOT NULL) AND (new_value <> ''::text))
   ->  Bitmap Index Scan on node_id_idx  (cost=0.00..8842.88 rows=434276 width=0)
         Index Cond: (node_id = ANY ('{351,169,664,240}'::integer[]))
(5 rows)

I'm still a bit surprised by how different the query plan came out with what would seem like a minor change. 

Reuven