Re: [HACKERS] Autovacuum launcher occurs error when cancelled by SIGINT

On Fri, Jun 23, 2017 at 3:01 AM, Thomas Munro
<thomas.munro@enterprisedb.com> wrote:
> On Thu, Jun 22, 2017 at 4:29 AM, Kuntal Ghosh
> <kuntalghosh.2007@gmail.com> wrote:
>> On Wed, Jun 21, 2017 at 7:52 PM, Dilip Kumar <dilipbalaut@gmail.com> wrote:
>>> On Wed, Jun 21, 2017 at 7:47 PM, Kuntal Ghosh
>>> <kuntalghosh.2007@gmail.com> wrote:
>>>>> IMHO, It's not a good idea to use DSM call to verify the DSA handle.
>>>>>
>>>> Okay. Is there any particular scenario you've in mind where this may fail?
>>>
>>> It's not about failure, but about the abstraction.  When we are using
>>> the DSA we should not directly access the DSM which is under DSA.
>>>
>> Okay. I thought that I've found at least one usage of
>> dsm_find_mapping() in the code. :-)
>>
>> But, I've some more doubts.
>> 1. When should we use dsm_find_mapping()? (The first few lines of
>> dsm_attach is same as dsm_find_mapping().)
>> 2. As a user of dsa, how should we check whether my dsa handle is
>> already attached? I guess this is required because, if a user tries to
>> re-attach a dsa handle,  it's punishing the user by throwing an error
>> and the user wants to avoid such errors.
>
> I thought about this when designing the DSA API.  I couldn't think of
> any good reason to provide an 'am-I-already-attached?' function
> equivalent to dsm_find_mapping.  It seemed to me that the client code
> shouldn't ever be in any doubt about whether it's attached, and that
> wilfully or absent-mindedly throwing away dsa_area pointers and having
> to ask for them again doesn't seem like a very good design.  I suspect
> the same applies to dsm_find_mapping, and I don't see any callers in
> the source tree or indeed anywhere on the internet (based on a quick
> Google search).  But I could be missing something.
>
Thanks a lot for the clarification.


-- 
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com