Re: Introduce XID age and inactive timeout based replication slot invalidation

On Mon, Mar 25, 2024 at 11:53 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Mon, Mar 25, 2024 at 10:33 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> >
> > On Sun, Mar 24, 2024 at 3:06 PM Bharath Rupireddy
> > <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> > >
> > > I've attached the v18 patch set here.

I have one concern, for synced slots on standby, how do we disallow
invalidation due to inactive-timeout immediately after promotion?

For synced slots, last_inactive_time and inactive_timeout are both
set. Let's say I bring down primary for promotion of standby and then
promote standby, there are chances that it may end up invalidating
synced slots (considering standby is not brought down during promotion
and thus inactive_timeout may already be past 'last_inactive_time'). I
tried with smaller unit of inactive_timeout:

--Shutdown primary to prepare for planned promotion.

--On standby, one synced slot with last_inactive_time (lat) as 12:21
slot_name | failover | synced | active | temp | conf | res |
lat | inactive_timeout
---------------+----------+--------+--------+------+------+-----+----------------------------------+------------------
logical_slot1 | t | t | f | f |
f | | 2024-03-25 12:21:09.020757+05:30 | 60

--wait for some time, now the time is 12:24
postgres=# select now();
now
----------------------------------
2024-03-25 12:24:17.616716+05:30

-- promote immediately:
./pg_ctl -D ../../standbydb/ promote -w

--on promoted standby:
postgres=# select pg_is_in_recovery();
pg_is_in_recovery
-------------------
f

--synced slot is invalidated immediately on promotion.
slot_name | failover | synced | active | temp | conf
| res | lat |
inactive_timeout
---------------+----------+--------+--------+------+------+------------------+----------------------------------+--------
logical_slot1 | t | t | f | f
| f | inactive_timeout | 2024-03-25
12:21:09.020757+05:30 |

thanks
Shveta