Thread: Avoid call MaintainOldSnapshotTimeMapping, if old_snapshot_threshold is disabled.
Avoid call MaintainOldSnapshotTimeMapping, if old_snapshot_threshold is disabled.
From
Ranier Vilela
Date:
Hi,
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.
Since old_snapshot_threshold is -1, it is disabled, so MaintainOldSnapshotTimeMapping doesn't need to be run, right?
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.
Since old_snapshot_threshold is -1, it is disabled, so MaintainOldSnapshotTimeMapping doesn't need to be run, right?
regards,
Ranier Vilela
Attachment
Re: Avoid call MaintainOldSnapshotTimeMapping, if old_snapshot_threshold is disabled.
From
Andres Freund
Date:
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
Re: Avoid call MaintainOldSnapshotTimeMapping, if old_snapshot_threshold is disabled.
From
Ranier Vilela
Date:
Em qui., 17 de jun. de 2021 às 22:08, Andres Freund <andres@anarazel.de> escreveu:
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.
True. My mistake.
I didn't check GetSnapshotDataInitOldSnapshot correctly.
regards,
Ranier Vilela