I like this idea in general. I'm envisioning a cool explain display in 
pgAdmin that's updated live, as the query is executed, showing how many 
tuples a seq scan in the bottom, and an aggregate above it, has 
processed. Drool.

Currently the interface is that you open a new connection, and signal 
the backend using the same mechanism as a query cancel. That's fine for 
the interactive psql use case, but seems really heavy-weight for the 
pgAdmin UI I'm envisioning. You'd have to poll the server, opening a new 
connection each time. Any ideas on that? How about a GUC to send the 
information automatically every n seconds, for example?

Other than that, this one seems to be the most serious issue:

Tom Lane wrote:
> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
>> There are downsides: 
> 
> Insurmountable ones at that.  This one already makes it a non-starter:
> 
>> a) the overhead of counting rows and loops is there for every query execution,
>> even if you don't do explain analyze.

I wouldn't be surprised if the overhead of the counters turns out to be 
a non-issue, but we'd have to see some testing of that. InstrEndLoop is 
the function we're worried about, right?

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

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• Re: EXPLAIN progress info at 2008-04-09 01:15:34 from Tom Lane

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