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

On Thu, Jun 22, 2017 at 1:29 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.

From a logical point of view, there is nothing preventing the use of
dsm_find_mapping() on a DSA handle, still the API layering looks wrong
if you want to check for an existing mapping. So why not defining a
new API, like dsa_find_mapping() that just wraps dsm_find_mapping()
but has its own error handling? This would offer more flexibility for
the future.
-- 
Michael