Re: [WIP] Effective storage of duplicates in B-tree index.

29.01.2016 19:01, Thom Brown:
> On 29 January 2016 at 15:47, Aleksander Alekseev
> <a(dot)alekseev(at)postgrespro(dot)ru> wrote:
>> I tested this patch on x64 and ARM servers for a few hours today. The
>> only problem I could find is that INSERT works considerably slower after
>> applying a patch. Beside that everything looks fine - no crashes, tests
>> pass, memory doesn't seem to leak, etc.
Thank you for testing. I rechecked that, and insertions are really very
very very slow. It seems like a bug.
>>> Okay, now for some badness. I've restored a database containing 2
>>> tables, one 318MB, another 24kB. The 318MB table contains 5 million
>>> rows with a sequential id column. I get a problem if I try to delete
>>> many rows from it:
>>> # delete from contacts where id % 3 != 0 ;
>>> WARNING: out of shared memory
>>> WARNING: out of shared memory
>>> WARNING: out of shared memory
>> I didn't manage to reproduce this. Thom, could you describe exact steps
>> to reproduce this issue please?
> Sure, I used my pg_rep_test tool to create a primary (pg_rep_test
> -r0), which creates an instance with a custom config, which is as
> follows:
>
> shared_buffers = 8MB
> max_connections = 7
> wal_level = 'hot_standby'
> cluster_name = 'primary'
> max_wal_senders = 3
> wal_keep_segments = 6
>
> Then create a pgbench data set (I didn't originally use pgbench, but
> you can get the same results with it):
>
> createdb -p 5530 pgbench
> pgbench -p 5530 -i -s 100 pgbench
>
> And delete some stuff:
>
> thom(at)swift:~/Development/test$ psql -p 5530 pgbench
> Timing is on.
> psql (9.6devel)
> Type "help" for help.
>
>
> ➤ psql://thom(at)[local]:5530/pgbench
>
> # DELETE FROM pgbench_accounts WHERE aid % 3 != 0;
> WARNING: out of shared memory
> WARNING: out of shared memory
> WARNING: out of shared memory
> WARNING: out of shared memory
> WARNING: out of shared memory
> WARNING: out of shared memory
> WARNING: out of shared memory
> ...
> WARNING: out of shared memory
> WARNING: out of shared memory
> DELETE 6666667
> Time: 22218.804 ms
>
> There were 358 lines of that warning message. I don't get these
> messages without the patch.
>
> Thom

Thank you for this report.
I tried to reproduce it, but I couldn't. Debug will be much easier now.

I hope I'll fix these issueswithin the next few days.

BTW, I found a dummy mistake, the previous patch contains some unrelated
changes. I fixed it in the new version (attached).

--
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company