Peter Geoghegan wrote:
On Tue, Apr 10, 2018 at 5:45 PM, Peter Geoghegan <p...@bowt.ie> wrote:
I did find another problem, though. Looks like the idea to explicitly
represent the number of attributes directly has paid off already:
pg@~[3711]=# create table covering_bug (f1 int, f2 int, f3 text);
create unique index cov_idx on covering_bug (f1) include(f2);
insert into covering_bug select i, i * random() * 1000, i * random() *
100000 from generate_series(0,100000) i;
DEBUG: building index "pg_toast_16451_index" on table "pg_toast_16451" serially
CREATE TABLE
DEBUG: building index "cov_idx" on table "covering_bug" serially
CREATE INDEX
ERROR: tuple has wrong number of attributes in index "cov_idx"
Actually, this was an error on my part (though I'd still maintain that
the check paid off here!). I'll still add defensive assertions inside
_bt_newroot(), and anywhere else that they're needed. There is no
reason to not add defensive assertions in all code that handles page
splits, and needs to fetch a highkey from some other page. We missed a
few of those.
Agree, I prefer to add more Assert, even. may be, more than actually
needed. Assert-documented code :)
I'll add an item to "Decisions to Recheck Mid-Beta" section of the
open items page for this patch. We should review the decision to make
a call to _bt_check_natts() within _bt_compare(). It might work just
as well as an assertion, and it would be unfortunate if workloads that
don't use covering indexes had to pay a price for the
_bt_check_natts() call, even if it was a small price. I've seen
_bt_compare() appear prominently in profiles quite a few times.
Could you show a patch?
I think, we need move _bt_check_natts() and its call under
USE_ASSERT_CHECKING to prevent performance degradation. Users shouldn't
pay for unused feature.
--
Teodor Sigaev E-mail: teo...@sigaev.ru
WWW: http://www.sigaev.ru/
