Обсуждение: Avoid call MaintainOldSnapshotTimeMapping, if old_snapshot_threshold is disabled.

Hi,

On 2021-06-17 21:27:15 -0300, Ranier Vilela wrote:
> While another long thread discusses the situation of old_snapshot_threshold,
> I believe we can improve procarray.c by avoiding calling
> MaintainOldSnapshotTimeMapping (src/backend/utils/time/snapmgr.c).
> 
> There's a very explicit comment there, which says (line 1866):
> "Never call this function when old snapshot checking is disabled."
> 
> Well, assert should never be used to validate a condition that certainly
> occurs at runtime.

I don't see how it can happen at runtime currently?

> Since old_snapshot_threshold is -1, it is disabled, so
> MaintainOldSnapshotTimeMapping doesn't need to be run, right?

It *isn't* run, the caller checks OldSnapshotThresholdActive() first.

Greetings,

Andres Freund