Re: Freeing sortgroupatts in use_physical_tlist

Zhihong Yu <zyu(at)yugabyte(dot)com> writes:
> I was looking at the code in use_physical_tlist().
> In the code block checking CP_LABEL_TLIST, I noticed that
> the Bitmapset sortgroupatts is not freed before returning from the method.
> Looking at create_foreignscan_plan() (in the same file):
> bms_free(attrs_used);
> It seems the intermediate Bitmapset is freed before returning.

TBH, I'd say that it's probably the former code not the latter
that is good practice. Retail pfree's in code that's not in a
loop very possibly expend more cycles than they are worth, because
the space will get cleaned up anyway when the active memory
context is reset, and pfree is not as cheap as one might wish.
It might be possible to make a case for one method over the other
with some study of the particular situation, but you can't say
a priori which way is better.

On the whole, I would not bother changing either of these bits
of code without some clear evidence that it matters. It likely
doesn't. It's even more likely that it doesn't matter enough
to be worth investigating.

regards, tom lane