On Wednesday, October 21, 2020, Bharath Rupireddy <
bharath.rupireddyforpostgres@gmail.com> wrote:
Thanks for the feedback.
On Wed, Oct 21, 2020 at 8:01 PM David G. Johnston
<david.g.johnston@gmail.com> wrote:
>
> On Wed, Oct 21, 2020 at 6:13 AM Magnus Hagander <magnus@hagander.net> wrote:
>>
>> I think it would be nicer to have a pg_terminate_backend(pid, wait=false), so a function with a second parameter which defaults to the current behaviour of not waiting. And it might be a good idea to also give it a timeout parameter?
>
> Agreed on the overload, and the timeouts make sense too - with the caller deciding whether a timeout results in a failure or a false return value.
>
If the backend is terminated within the user specified timeout then
the function returns true, otherwise false.
I’m suggesting an option for the second case to fail instead of returning false.
>
>>> 2. pg_wait_backend() -- which waits for a given backend process. Note that this function has to be used carefully after pg_terminate_backend(), if used on a backend that's not ternmited it simply keeps waiting in a loop.
>>
>> It seems this one also very much would need a timeout value.
>
> Is there a requirement for waiting to be superuser only? You are not affecting any session but your own during the waiting period.
>
IIUC, in the same patch instead of returning an error in case of
non-superusers, do we need to wait for user provided timeout
milliseconds until the current user becomes superuser and then throw
error if still non-superuser, and proceed further if superuser?
Do we need to have a new function that waits until a current
non-superuser in a session becomes superuser?
Something else?
Not sure how that would even be possible mid-statement. I was suggesting removing the superuser check altogether and letting any user execute “wait”.
>
> I could imagine, in theory at least, wanting to wait for a backend to go idle as well as for it disappearing. Scope creep in terms of this patch's goal but worth at least considering now.
>
IIUC, do we need a new option, something like pg_wait_backend(pid,
timeout, waituntil) where "waituntil" if specified "idle" waits until
the given backend goes to idle mode, or "termination" waits until
termination?
If my understanding is wrong, could you please explain more?
Yes, this describes what i was thinking.
David J.