Re: Parallel Seq Scan

On Fri, Oct 16, 2015 at 2:10 PM, Haribabu Kommi
<kommi(dot)haribabu(at)gmail(dot)com> wrote:
> On Thu, Oct 15, 2015 at 11:45 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> On Thu, Oct 15, 2015 at 5:39 PM, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
>> wrote:
>>>
>>>
>>>
>>> On Thu, Oct 15, 2015 at 6:32 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
>>> wrote:
>>> > On Wed, Oct 14, 2015 at 3:29 AM, Robert Haas <robertmhaas(at)gmail(dot)com>
>>> > wrote:
>>> > I think this got messed up while rebasing on top of Gather node
>>> > changes, but nonetheless, I have changed it such that PartialSeqScan
>>> > node handling is after SeqScan.
>>>
>>> Currently, the explain analyze of parallel seq scan plan is not showing
>>> the allocated number of workers
>>> including the planned workers.I feel this information is good for users in
>>> understanding the performance
>>> difference that is coming with parallel seq scan. It may be missed in
>>> recent patch series. It was discussed
>>> in[1].
>>>
>>
>> I am aware of that and purposefully kept it for a consecutive patch.
>> There are other things as well which I have left out from this patch
>> and those are:
>> a. Early stop of executor for Rescan purpose
>> b. Support of pushdown for plans containing InitPlan and SubPlans
>>
>> Then there is more related work like
>> a. Support for prepared statements
>>
>
> OK.
>
> During the test with latest patch, I found a dead lock between worker
> and backend
> on relation lock. To minimize the test scenario, I changed the number
> of pages required
> to start one worker to 1 and all parallel cost parameters as zero.
>
> Backend is waiting for the tuples from workers, workers are waiting on
> lock of relation.
> Attached is the sql script that can reproduce this issue.

Some more tests that failed in similar configuration settings.
1. Table that is created under a begin statement is not visible in the worker.
2. permission problem in worker side for set role command.

Regards,
Hari Babu
Fujitsu Australia