Re: WAL usage calculation patch

On Tue, Mar 31, 2020 at 7:39 PM Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
>
> On Tue, Mar 31, 2020 at 12:21 PM Kuntal Ghosh
> <kuntalghosh(dot)2007(at)gmail(dot)com> wrote:
> >
> > On Mon, Mar 30, 2020 at 6:14 PM Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
> > >
> > @@ -448,6 +449,7 @@ XLogInsert(RmgrId rmid, uint8 info)
> > bool doPageWrites;
> > XLogRecPtr fpw_lsn;
> > XLogRecData *rdt;
> > + int num_fpw = 0;
> >
> > /*
> > * Get values needed to decide whether to do full-page writes. Since
> > @@ -457,9 +459,9 @@ XLogInsert(RmgrId rmid, uint8 info)
> > GetFullPageWriteInfo(&RedoRecPtr, &doPageWrites);
> >
> > rdt = XLogRecordAssemble(rmid, info, RedoRecPtr, doPageWrites,
> > - &fpw_lsn);
> > + &fpw_lsn, &num_fpw);
> >
> > - EndPos = XLogInsertRecord(rdt, fpw_lsn, curinsert_flags);
> > + EndPos = XLogInsertRecord(rdt, fpw_lsn, curinsert_flags, num_fpw);
> > } while (EndPos == InvalidXLogRecPtr);
> >
> > I think there are some issues in the num_fpw calculation. For some
> > cases, we have to return from XLogInsert without inserting a record.
> > Basically, we've to recompute/reassemble the same record. In those
> > cases, num_fpw should be reset. Thoughts?
>
> Mmm, yes but since that's the same record is being recomputed from the
> same RedoRecPtr, doesn't it mean that we need to reset the counter?
> Otherwise we would count the same FPW multiple times.

Yes. That was my point as well. I missed the part that you're already
resetting the same inside the do-while loop before calling
XLogRecordAssemble. Sorry for the noise.