Re: Duplicate Item Pointers in Gin index

On Wed, Jun 13, 2018 at 3:32 PM, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> On Tue, Jun 12, 2018 at 11:01 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>> FWIW, I've looked at this again. I think that the situation Siva
>> reported in the first mail can happen before we get commit 3b2787e.
>> That is, gin indexes had had a data corruption bug. I've reproduced
>> the situation with PostgreSQL 10.1 and observed that a gin index can
>> corrupt.
>
> So, you've recreated the problem with Postgres from before 3b2787e,
> but not after 3b2787e? Are you suggesting that 3b2787e might have
> fixed it, or that it only hid the problem, or something else?

I meant 3b2787e fixed it. I checked that at least the situation
doesn't happen after 3b2787e.

> How did you recreate the problem? Do you have a test case you can share?

I recreated it by executing each steps step by step using gdb. So I
can share the test case but it might not help.

create extension pageinspect;
create table g (c int[]);
insert into g select ARRAY[1] from generate_series(1,1000);
create index g_idx on g using gin (c);
alter table g set (autovacuum_enabled = off);
insert into g select ARRAY[1] from generate_series(1, 408); -- 408
items fit in exactly one page of pending list
insert into g select ARRAY[1] from generate_series(1, 100); -- insert
into 2nd page of pending list
select n_pending_pages, n_pending_tuples from
gin_metapage_info(get_raw_page('g_idx', 0));
insert into g select ARRAY[999]; -- insert into 2nd pending list page
delete from g where c = ARRAY[999];
-- At this point, gin entry of 'ARRAY[999]' exists on 2nd page of
pending list and deleted.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center