Re: Index seems "lost" after consecutive deletes

Em 13/06/2016 22:33, Edson Richter escreveu:
> I've a table "A" with 4,000,000 records.
>
> I've decided to delete records from oldest to newest but I can't
> delete records that have references in tables "B", "C" or "D".
>
>
> so, I've
>
>
> with qry as (
>
>     select A.id
>
>       from A
>
>     where not exists (select 1 from B where B.a_id = A.id)
>
>        and not exists (select 1 from C where C.a_id = A.id)
>
>        and not exists (select 1 from D where D.a_id = A.id)
>
>        and A.creation_date < (now()::date - interval '12 month')
>
>   order by A.id DESC
>
>   limit 2000
>
> )
>
> delete from A where id in (select id from qry);
>
>
> All three referenced tables have indexes (B.a_id; C.a_id; D.a_id) in
> order to make query faster.
>
> So for first 2 million rows it worked really well, taking about 1
> minute to delete each group of 2000 records.
>
> Then, after a while I just started to get errors like:
>
>
> ERROR: update or delete in "A" violates foreign key "fk_C_A" in "C".
>
> DETAIL:  Key (id)=(3240124) is still referenced by table "C".
>
>
> Seems to me that indexes got lost in the path - the query is really
> specific and no "C" referenced records can be in my deletion.
>
> Has anyone faced a behavior like this?
>
> Am I doing something wrong?
>
>

Of course:
Version string    PostgreSQL 9.4.8 on x86_64-unknown-linux-gnu, compiled
by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4), 64-bit
Oracle Linux 7 x64 with all updates. Running on EXT4 file system.
Computer is Dell R420 with mirrored disks, 80GB of RAM (database has <
40GB in total).

Sorry for not putting the info in the first e-mail.

Edson