Re: 12.3 replicas falling over during WAL redo

On 2020-Aug-03, Alvaro Herrera wrote:

> >      lsn      | checksum | flags | lower | upper | special | pagesize |
> > version | prune_xid
> > --------------+----------+-------+-------+-------+---------+----------+---------+-----------
> >  A0A/99BA11F8 |     -215 |     0 |   180 |  7240 |    8176 |     8192
> > |       4 |         0
> >
> > As I understand what we're looking at, this means the WAL stream was
> > assuming this page was last touched by A0A/AB2C43D0, but the page itself
> > thinks it was last touched by A0A/99BA11F8, which means at least one write
> > to the page is missing?
>
> Yeah, that's exactly what we're seeing. Somehow an older page version
> was resurrected. Of course, this should never happen.

... although, the block should have been in shared buffers, and it is
there that the previous WAL record would have updated -- not necessarily
flushed to disk.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services