Re: [HACKERS] Parallel Append implementation

From: Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>
To: Rafia Sabih <rafia(dot)sabih(at)enterprisedb(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Parallel Append implementation
Date: 2017-11-21 08:52:57
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On 21 November 2017 at 12:44, Rafia Sabih <rafia(dot)sabih(at)enterprisedb(dot)com> wrote:
> On Mon, Nov 13, 2017 at 12:54 PM, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com> wrote:
>> Thanks a lot Robert for the patch. I will have a look. Quickly tried
>> to test some aggregate queries with a partitioned pgbench_accounts
>> table, and it is crashing. Will get back with the fix, and any other
>> review comments.
>> Thanks
>> -Amit Khandekar
> I was trying to get the performance of this patch at commit id -
> 11e264517dff7a911d9e6494de86049cab42cde3 and TPC-H scale factor 20
> with the following parameter settings,
> work_mem = 1 GB
> shared_buffers = 10GB
> effective_cache_size = 10GB
> max_parallel_workers_per_gather = 4
> enable_partitionwise_join = on
> and the details of the partitioning scheme is as follows,
> tables partitioned = lineitem on l_orderkey and orders on o_orderkey
> number of partitions in each table = 10
> As per the explain outputs PA was used in following queries- 1, 3, 4,
> 5, 6, 7, 8, 10, 12, 14, 15, 18, and 21.
> Unfortunately, at the time of executing any of these query, it is
> crashing with the following information in core dump of each of the
> workers,
> Program terminated with signal 11, Segmentation fault.
> #0 0x0000000010600984 in pg_atomic_read_u32_impl (ptr=0x3ffffec29294)
> at ../../../../src/include/port/atomics/generic.h:48
> 48 return ptr->value;
> In case this a different issue as you pointed upthread, you may want
> to have a look at this as well.
> Please let me know if you need any more information in this regard.

Right, for me the crash had occurred with a similar stack, although
the real crash happened in one of the workers. Attached is the script
pgbench_partitioned.sql to create a schema with which I had reproduced
the crash.

The query that crashed :
select sum(aid), avg(aid) from pgbench_accounts;

Set max_parallel_workers_per_gather to at least 5.

Also attached is v19 patch rebased.

-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company

Attachment Content-Type Size
pgbench_partitioned.sql application/octet-stream 1.1 KB
ParallelAppend_v19_rebased.patch application/octet-stream 57.7 KB

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