Re: WAL usage calculation patch

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.