Re: Very specialised query

>
>
> The outer nested join has the VALUES as the main loop, and the complicated
> join as the leaf. So, the complicated overlap-finding join gets run twice.

That's weird. What do you have as statistics target? Planner is incorrect
few orders of magnitude, so increasing it may help.
BTW: One of constraints is redundant l1.start <= l2.start implies l1.start
<= l2.end, so latter can be removed as for me.

>
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> Oh, there's also the great big sort and unique, but I think I can get rid
> of that.
>

As far as I can see, duplicates will occur if and only if l1.start ==
l2.start && l1.end == l2.end.
That can be easily filtered by adding "where n=1 or l1.start != l2.start or
l1.end != l2.end" to outer select.