Re: [HACKERS] Re: [BUGS] General Bug Report: palloc fails with lots of ANDs and ORs

Added to TODO list.


>
> > >
> > > select count(*) from outlet
> > > where
> > >     (number = 1 and number = 1 and number = 1) or
> > >     (number = 1 and number = 1 and number = 1) or
> > >     (number = 1 and number = 1 and number = 1) or
> > >     (number = 1 and number = 1 and number = 1) or
> > >     (number = 1 and number = 1 and number = 1) or
> > >     (number = 1 and number = 1 and number = 1) or
> > >     (number = 1 and number = 1 and number = 1) or
> > >     (number = 1 and number = 1 and number = 1) or
> > >     (number = 1 and number = 1 and number = 1);
> > >
> > > Not pretty but it makes the point.   Take out two OR clauses and the query
> > > works fine (but a bit slow).
> > >
> > > The above query is all it takes to use up all 130000 Kbytes of memory.
> > > And, since the query takes a long time to finally fail, I was able to
> > > observe the memory consumption.
>
> Optimizator tries to transform qual above into AND clause with
> 3 (# of and-ed clauses) ^ 9 (# of OR-s) = 19683 args (each arg
> is OR clause with 9 op. expressions. My estimation for current
> cnfify() code is that this will require =~ 500Mb of memory :)
> I made little changes - just to free memory when it's possible:
>
>           current code                 with free-ing
>
> 6 ORs     14.3 Mb                      4.3 Mb
> 7 ORs     53 Mb                        10.3 Mb
> 8 ORs     estimation: ~ 160 Mb         30.6 MB
>
> I'm not sure should I aplly my changes or not - it doesn't fix
> problem, just reduces memory impact. It obviously can't help you,
> David, in your real example (3 ^ 28 = 22876792454961 clauses - he he :).
>
> Resume: cnfify() makes mathematically strong but in some cases
> practically unwise work. I can't fix this for 6.3
>
> Vadim
>


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