Re: BUG #14732: partitioned table cann't alter set parallel_workers?

HI,
Thank you for your reply, but i mean it's good for user if PG support ```alter partitioned table set (parallel_workers=?)``` syntax.
because there some partition tables sometimes, so direct set partition table is not comfortable.

best regards.

--
公益是一辈子的事,I'm Digoal,Just Do It.

At 2017-07-04 12:45:15, "Amit Langote" <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>Hi,
>
>On 2017/07/04 11:09, digoal(at)126(dot)com wrote:
>> The following bug has been logged on the website:
>>
>> Bug reference: 14732
>> Logged by: Zhou Digoal
>> Email address: digoal(at)126(dot)com
>> PostgreSQL version: 10beta1
>> Operating system: CentOS 6.x x64
>> Description:
>>
>> HI,
>>
>> there is an normal table and a partitiond table.
>> normal table can set parallel_works parameter, but partitioned table
>> cann't.
>>
>> ```
>> postgres=# \d orders
>> Unlogged table "public.orders"
>> Column | Type | Collation | Nullable |
>> Default
>> -----------------+-----------------------+-----------+----------+--------------------------------------------
>> o_orderkey | bigint | | not null |
>> nextval('orders_o_orderkey_seq'::regclass)
>> o_custkey | bigint | | not null |
>> o_orderstatus | character(1) | | |
>> o_totalprice | double precision | | |
>> o_orderdate | date | | |
>> o_orderpriority | character(15) | | |
>> o_clerk | character(15) | | |
>> o_shippriority | integer | | |
>> o_comment | character varying(79) | | |
>>
>> postgres=# \d orders1
>> Unlogged table "public.orders1"
>> Column | Type | Collation | Nullable |
>> Default
>> -----------------+-----------------------+-----------+----------+---------------------------------------------
>> o_orderkey | bigint | | not null |
>> nextval('orders1_o_orderkey_seq'::regclass)
>> o_custkey | bigint | | not null |
>> o_orderstatus | character(1) | | |
>> o_totalprice | double precision | | |
>> o_orderdate | date | | |
>> o_orderpriority | character(15) | | |
>> o_clerk | character(15) | | |
>> o_shippriority | integer | | |
>> o_comment | character varying(79) | | |
>> Partition key: RANGE (o_orderdate)
>> Number of partitions: 84 (Use \d+ to list them.)
>>
>> postgres=# alter table orders set (parallel_workers =32);
>> ALTER TABLE
>> postgres=# alter table orders1 set (parallel_workers =32);
>> ERROR: 22023: unrecognized parameter "parallel_workers"
>> LOCATION: parseRelOptions, reloptions.c:1094
>> ```
>
>This is not really a bug. We do not support setting reloptions
>(parallel_workers is a reloption) for partitioned tables, because setting
>them will currently have no effect. Maybe the error message doesn't make
>that clear. It's actually trying to say: "parallel workers" is
>unrecognized parameter for partitioned tables.
>
>You can set them on the individual partitions.
>
>> but i can update pg_class to modify partitioned table's parallel_works.
>>
>> ```
>> postgres=# update pg_class set reloptions =array['parallel_workers=13']
>> where relname ~ 'lineitem' and relkind='r';
>> UPDATE 85
>
>Yes, you can to do that, but the system still won't use it. When
>appropriate system support for partitioned tables to use parallel query
>will be added, then we will also make the above alter table command
>succeed, but not until then.
>
>By the way, the update statement above doesn't actually affect partitioned
>tables, because its relkind is 'p'.
>
>> postgres=# explain select count(*) from lineitem1;
>> QUERY PLAN
>>
>> -----------------------------------------------------------------------------------------------------------
>> Finalize Aggregate (cost=130579654.20..130579654.21 rows=1 width=8)
>> -> Gather (cost=130579654.16..130579654.17 rows=13 width=8)
>> Workers Planned: 13
>> -> Partial Aggregate (cost=130579654.16..130579654.17 rows=1
>> width=8)
>> -> Append (cost=0.00..130557628.94 rows=8810089 width=0)
>> -> Parallel Seq Scan on lineitem_ptr_0
>> (cost=0.00..209424.27 rows=106127 width=0)
>> -> Parallel Seq Scan on lineitem_ptr_1
>> (cost=0.00..585852.15 rows=106115 width=0)
>> -> Parallel Seq Scan on lineitem_ptr_2
>> (cost=0.00..1043031.30 rows=106130 width=0)
>> -> Parallel Seq Scan on lineitem_ptr_3
>> (cost=0.00..1419621.31 rows=106131 width=0)
>> ...
>> ```
>
>Use of parallelism in this case may be the result of setting parallel
>workers on the individual partitions, that is, lineitem_ptr_* relations.
>
>Thanks,
>Amit
>