Hi, On Mon, Mar 25, 2024 at 08:38:16PM +0530, Amit Kapila wrote: > On Mon, Mar 25, 2024 at 7:51 PM Robert Haas <robertmh...@gmail.com> wrote: > > > > On Mon, Mar 25, 2024 at 10:02 AM Amit Kapila <amit.kapil...@gmail.com> > > wrote: > > > We considered the other two names as last_inactive_at and > > > last_active_time. For the first (last_inactive_at), there was an > > > argument that most other fields that display time ends with _time. For > > > the second (last_active_time), there was an argument that it could be > > > misleading as one could think that it should be updated each time WAL > > > record decoding is happening [1]. The other possibility is to name it > > > last_used_time but I think it won't be much different from > > > last_active_time. > > > > I don't understand the bit about updating it each time WAL record > > decoding is happening. If it's the last active time, and the slot is > > currently active, then the answer is either "right now" or "currently > > undefined." I'd expect to see NULL in the system view in such a case. > > And if that's so, then there's nothing to update each time a record is > > decoded, because it's just still going to show NULL. > > > > IIUC, Bertrand's point was that users can interpret last_active_time > as a value that gets updated each time they decode a change which is > not what we are doing. So, this can confuse users. Your expectation of > answer (NULL) when the slot is active is correct and that is what will > happen.
Yeah, and so would be the confusion: why is last_active_time NULL while one is using the slot? > > Why does this field get set to the current time when the slot is > > restored from disk? > > > > It is because we don't want to include the time the server is down in > the last_inactive_time. Say, if we are shutting down the server at > time X and the server remains down for another two hours, we don't > want to include those two hours as the slot inactive time. The related > theory is that this field will be used to invalidate inactive slots > based on a threshold (say inactive_timeout). Say, before the shutdown, > we release the slot and set the current_time for last_inactive_time > for each slot and persist that information as well. Now, if the server > is down for a long time, we may invalidate the slots as soon as the > server comes up. So, instead, we just set this field at the time we > read slots for disk and then reset it to 0/NULL as soon as the slot > became active. Right, and we also want to invalidate the slot if not used duration > timeout, so that setting the field to zero when the slot is restored from disk is also not an option. Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
