Re: Review for GetWALAvailability()

On 2020/06/25 3:27, Alvaro Herrera wrote:
> Thanks for those corrections.
>
> I have pushed this. I think all problems Masao-san reported have been
> dealt with, so we're done here.

Sorry for my late to reply here...

Thanks for committing the patch and improving the feature!

/*
* Find the oldest extant segment file. We get 1 until checkpoint removes
* the first WAL segment file since startup, which causes the status being
* wrong under certain abnormal conditions but that doesn't actually harm.
*/
oldestSeg = XLogGetLastRemovedSegno() + 1;

I see the point of the above comment, but this can cause wal_status to be
changed from "lost" to "unreserved" after the server restart. Isn't this
really confusing? At least it seems better to document that behavior.

Or if we *can ensure* that the slot with invalidated_at set always means
"lost" slot, we can judge that wal_status is "lost" without using fragile
XLogGetLastRemovedSegno(). Thought?

Or XLogGetLastRemovedSegno() should be fixed so that it returns valid
value even after the restart?

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION