On 2018-04-07 14:27, Alexander Korotkov wrote:
On Sat, Apr 7, 2018 at 2:57 PM, Erik Rijkers <e...@xs4all.nl> wrote:

On 2018-04-06 20:08, Alexander Korotkov wrote:


After some more testing I notice there is also a down-side/slow-down to this patch that is not so bad but more than negligible, and I don't think
it has been mentioned (but I may have missed something in this thread
that's now been running for 1.5 year, not to mention the tangential

I attach my test-program, which compares master (this morning) with
covered_indexes (warning: it takes a while to generate the used tables).

The test tables are created as:
  create table $t (c1 int, c2 int, c3 int, c4 int);
insert into $t (select x, 2*x, 3*x, 4 from generate_series(1, $rowcount)
as x);
  create unique index ${t}uniqueinclude_idx on $t using btree (c1, c2)
include (c3, c4);

or for HEAD, just:
  create unique index ${t}unique_idx on $t using btree (c1, c2);

Do I understand correctly that you compare unique index on (c1, c2) with master to unqiue index on (c1, c2) include (c3, c4) with patched version?
If so then I think it's wrong to say about down-side/slow-down of this
patch based on this comparison.
Patch *does not* cause slowdown in this case. Patch provides user a *new option* which has its advantages and disadvantages. And what you compare is advantages and disadvantages of this option, not slow-down of the patch.
In the case you compare *the same* index on master and patched version,
then it's possible to say about slow-down of the patch.

OK, I take your point -- you are right. Although my measurement was (I think) correct, my comparison was not (as Teodor wrote, not quite 'fair').

Sorry, I should have better thought that message through. The somewhat longer time is indeed just a disadvantage of this new option, to be balanced against the advantages that are pretty clear too.

Erik Rijkers

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