Re: PG and undo logging

On May 23, 2015 01:48:11 PM David G. Johnston wrote:

> On Sat, May 23, 2015 at 1:34 PM, Ravi Krishna <sravikrishna3@gmail.com>

>

> wrote:

> > Is it true that PG does not log undo information, only redo. If true,

> > then how does it bring a database back to consistent state during

> > crash recovery. Just curious.

>

> ​What does "undo" mean?

>

> David J.​

Methinks rolling back the changes that transactions which got interrupted by the crash scribbled onto the data file. It's an Oracleism where not-consolidated data is kept in undo- and redo datafiles.

While I roughly understand Postgres' MVCC I don't feel qualified to answer Ravi's question :-)