Re: increasing collapse_limits? - Mailing list pgsql-hackers

From Robert Haas
Subject Re: increasing collapse_limits?
Date
Msg-id 4F274948-F668-4534-B40C-F3FC5DAAA782@gmail.com
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In response to Re: increasing collapse_limits?  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
On Apr 30, 2011, at 10:21 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> It also occurs to me to wonder if we could adjust the limit on-the-fly
> based on noticing whether or not the query is prone to worst-case
> behavior, ie how dense is the join connection graph.

I've had this thought - or a similar one - before also. I am not sure how to make it work mechanically but I think it
wouldbe tremendous if we could make it work. For most people, my previous naive suggestion (remove the limit entirely)
wouldactually work fine, BUT if you hit the problem cases then even a small increase is too much. So I don't really
thinkincreasing the limit will eliminate  the need for manual fiddling - what we really need to do is come up with a
moreaccurate measure of measure of complexity than "number of tables". 

...Robert

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