Thread: show xl_prev in xlog.c errcontext
I found this patch in my local repo that I wrote some weeks or months ago while debugging some XLog corruption problem: it was difficult to pinpoint what XLog record in a long sequence of WAL files was causing a problem, and the displaying the prev pointer in errcontext made finding it much easier -- I could correlate it with pg_xlogdump output, I think. Anyone sees a reason not to apply this or something like it? (As I recall, we eventually found out that the underlying issue was that two postmasters shared one data area over NFS and were overwriting one another's WAL files, or something like that. But this was some time ago so I could be mistaken that it's the same case.) -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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On 04/15/2015 11:35 PM, Alvaro Herrera wrote: > I found this patch in my local repo that I wrote some weeks or months > ago while debugging some XLog corruption problem: it was difficult to > pinpoint what XLog record in a long sequence of WAL files was causing a > problem, and the displaying the prev pointer in errcontext made finding > it much easier -- I could correlate it with pg_xlogdump output, I think. Seems like a good idea, but why print the prev pointer, and not the location of the record itself? - Heikki
On Thu, Apr 16, 2015 at 3:25 PM, Heikki Linnakangas <hlinnaka@iki.fi> wrote: > On 04/15/2015 11:35 PM, Alvaro Herrera wrote: >> >> I found this patch in my local repo that I wrote some weeks or months >> ago while debugging some XLog corruption problem: it was difficult to >> pinpoint what XLog record in a long sequence of WAL files was causing a >> problem, and the displaying the prev pointer in errcontext made finding >> it much easier -- I could correlate it with pg_xlogdump output, I think. > > > Seems like a good idea, but why print the prev pointer, and not the location > of the record itself? And both? -- Michael
Michael Paquier wrote: > On Thu, Apr 16, 2015 at 3:25 PM, Heikki Linnakangas <hlinnaka@iki.fi> wrote: > > On 04/15/2015 11:35 PM, Alvaro Herrera wrote: > >> > >> I found this patch in my local repo that I wrote some weeks or months > >> ago while debugging some XLog corruption problem: it was difficult to > >> pinpoint what XLog record in a long sequence of WAL files was causing a > >> problem, and the displaying the prev pointer in errcontext made finding > >> it much easier -- I could correlate it with pg_xlogdump output, I think. > > > > Seems like a good idea, but why print the prev pointer, and not the location > > of the record itself? Makes sense -- pushed that way. > And both? I couldn't see much point of doing this, so I didn't. If you have a rationale for it, let's hear it. -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
On Tue, Apr 5, 2016 at 6:14 AM, Alvaro Herrera <alvherre@2ndquadrant.com> wrote: > Michael Paquier wrote: >> And both? > > I couldn't see much point of doing this, so I didn't. If you have a > rationale for it, let's hear it. Now that I think on it, it does not actually matter to print both. -- Michael