From: | Thom Brown <thom(at)linux(dot)com> |
---|---|
To: | Aleksander Alekseev <a(dot)alekseev(at)postgrespro(dot)ru> |
Cc: | Anastasia Lubennikova <a(dot)lubennikova(at)postgrespro(dot)ru>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [WIP] Effective storage of duplicates in B-tree index. |
Date: | 2016-01-29 16:01:37 |
Message-ID: | CAA-aLv7pmO41G78jfLsftsCvkXZw6dL8HZoCX9ute6nQxJv2tw@mail.gmail.com |
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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.
>
>> 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
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