Re: Add LSN along with offset to error messages reported for WAL file read/write/validate header failures

On Tue, 15 Nov 2022 at 13:02, Bharath Rupireddy <
bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:

> On Fri, Nov 11, 2022 at 5:52 PM Maxim Orlov <orlovmg(at)gmail(dot)com> wrote:
>
> > But, in my view, some improvements may be proposed. We should be more,
> let's say, cautious (or a paranoid if you wish),
> > in pg_walfile_offset_lsn while dealing with user input values. What I
> mean by that is:
> > - to init input vars of sscanf, i.e. tli, log andseg;
> > - check the return value of sscanf call;
> > - check filename max length.
>
> IsXLogFileName() will take care of this. Also, I've added a new inline
> function XLogIdFromFileName() that parses file name and returns log
> and seg along with XLogSegNo and timeline id. This new function avoids
> an extra sscanf() call as well.
>
> > Another question arises for me: is this function can be called during
> recovery? If not, we should ereport about this, should we?
>
> It's just a utility function and doesn't depend on any of the server's
> current state (unlike pg_walfile_name()), hence it doesn't matter if
> this function is called during recovery.
>
> > And one last note here: pg_walfile_offset_lsn is accepting NULL values
> and return NULL in this case. From a theoretical
> > point of view, this is perfectly fine. Actually, I think this is exactly
> how it supposed to be, but I'm not sure if there are no other opinions here.
>
> These functions are marked as 'STRICT', meaning a null is returned,
> without even calling the function, if any of the input parameters is
> null. I think we can keep the behaviour the same as its friends.
>

Thanks for the explanations. I think you are right.

> > errmsg("offset must not be negative or greater than or equal to the
> WAL segment size")));
>
> Changed.
>

Confirm. And a timeline_id is added.

> While on this, I noticed that the pg_walfile_name_offset() isn't
> covered in tests. I took an opportunity and added a simple test case
> along with pg_walfile_offset_lsn().
>
> I'm attaching the v3 patch set for further review.
>

Great job! We should mark this patch as RFC, shall we?

--
Best regards,
Maxim Orlov.