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

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.

The same pattern is seen in the tree.

Regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center