Re: [Patch] Optimize dropping of relation buffers using dlist

On Wed, Dec 23, 2020 at 10:42 AM Kyotaro Horiguchi
<horikyota(dot)ntt(at)gmail(dot)com> wrote:
>
> At Wed, 23 Dec 2020 04:22:19 +0000, "tsunakawa(dot)takay(at)fujitsu(dot)com" <tsunakawa(dot)takay(at)fujitsu(dot)com> wrote in
> > From: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> > > + /* Get the number of blocks for a relation's fork */
> > > + block[i][j] = smgrnblocks(smgr_reln[i], j, &cached);
> > > +
> > > + if (!cached)
> > > + goto buffer_full_scan;
> > >
> > > Why do we need to use goto here? We can simply break from the loop and
> > > then check if (cached && nBlocksToInvalidate <
> > > BUF_DROP_FULL_SCAN_THRESHOLD). I think we should try to avoid goto if
> > > possible without much complexity.
> >
> > That's because two for loops are nested -- breaking there only exits the inner loop. (I thought the same as you at first... And I understand some people have alergy to goto, I think modest use of goto makes the code readable.)
>
> I don't strongly oppose to goto's but in this case the outer loop can
> break on the same condition with the inner loop, since cached is true
> whenever the inner loop runs to the end. It is needed to initialize
> the variable cache with true, instead of false, though.
>

+1. I think it is better to avoid goto here as it can be done without
introducing any complexity or making code any less readable.

--
With Regards,
Amit Kapila.