Re: Parallel Bitmap Heap Scans segfaults due to (tbm->dsa==NULL) on PostgreSQL 10

On 10/12/2017 02:40 PM, Dilip Kumar wrote:
> On Thu, Oct 12, 2017 at 4:31 PM, Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>> Hi,
>>
>> It seems that Q19 from TPC-H is consistently failing with segfaults due
>> to calling tbm_prepare_shared_iterate() with (tbm->dsa==NULL).
>>
>> I'm not very familiar with how the dsa is initialized and passed around,
>> but I only see the failures when the bitmap is constructed by a mix of
>> BitmapAnd and BitmapOr operations.
>>
> I think I have got the issue, bitmap_subplan_mark_shared is not
> properly pushing the isshared flag to lower level bitmap index node,
> and because of that tbm_create is passing NULL dsa while creating the
> tidbitmap. So this problem will come in very specific combination of
> BitmapOr and BitmapAnd when BitmapAnd is the first subplan for the
> BitmapOr. If BitmapIndex is the first subplan under BitmapOr then
> there is no problem because BitmapOr node will create the tbm by
> itself and isshared is set for BitmapOr.
>
> Attached patch fixing the issue for me. I will thoroughly test this
> patch with other scenario as well. Thanks for reporting.
>

Yep, this fixes the failures for me.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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