Re: Alias collision in `refresh materialized view concurrently`

On Thu, May 20, 2021 at 09:14:45PM +0530, Bharath Rupireddy wrote:
> On Thu, May 20, 2021 at 7:52 PM Bernd Helmle <mailings(at)oopsware(dot)de> wrote:
>> "mv" looks like a very common alias (i use it all over the time when
>> testing or playing around with materialized views, so i'm wondering why
>> i didn't see this issue already myself). So the risk here for such a
>> collision looks very high. We can try to lower this risk by choosing an
>> alias name, which is not so common. With a static alias however you get
>> a static error condition, not something that fails here and then.
>
> Another idea is to use random() function to generate required number
> of uint32 random values(refresh_by_match_merge might need 3 values to
> replace newdata, newdata2 and mv) and use the names like
> pg_temp_rmv_<<rand_no1>>, pg_temp_rmv_<<rand_no2>> and so on. This
> would make the name unguessable. Note that we use this in
> choose_dsm_implementation, dsm_impl_posix.

I am not sure that I see the point of using a random() number here
while the backend ID, or just the PID, would easily provide enough
entropy for this internal alias. I agree that "mv" is a bad choice
for this alias name. One thing that comes in mind here is to use an
alias similar to what we do for dropped attributes, say
........pg.matview.%d........ where %d is the PID. This will very
unlikely cause conflicts.
--
Michael