> The mystery remains, for me: why updating 100,000 records could complete
> in as quickly as 5 seconds, whereas an attempt to update a million
> records was still running after 25 minutes before we killed it?
Hi, there's a lot of possible causes. Usually this is caused by a plan
change - imagine for example that you need to sort a table and the amount
of data just fits into work_mem, so that it can be sorted in memory. If
you need to perform the same query with 10x the data, you'll have to sort
the data on disk. Which is way slower, of course.
And there are other such problems ...
> One thing remains crystal clear: I love Postgresql :-)
regards
Tomas
