Обсуждение: Please humor me ...
And by the subject, I mean: please provide a "factual" answer, as opposed to the more or less obvious answer which would be "no one in their sane mind would even consider doing such thing" :-) 1) Would it be possible to entirely disable WAL? (something like setting a symlink so that pg_xlog points to /dev/null, perhaps?) 2) What would be the real implications of doing that? As I understand it, the WAL provide some sort of redundancy for fault- tolerance purposes; if my understanding is correct, then what kind of data loss are we talking about if I entirely disabled WAL and the machine running the DB cluster were to crash/freeze? What about a physical reboot (either a UPSless power-down, or someone pressing the reset button)? Or are we talking about the entire DB cluster possibly becoming corrupt beyond repair with 0% of the data being recoverable? Again, please bear with me ... I do know and understand the "no one in their sane mind would even consider doing such thing" aspect ... I'm for now interested in knowing more in detail the real facts behind this feature --- allow me to think outside the box for a little while :-) Thanks, Carlos --
On Mon, 2007-04-09 at 16:05 -0400, Carlos Moreno wrote: > And by the subject, I mean: please provide a "factual" answer, as opposed > to the more or less obvious answer which would be "no one in their sane > mind would even consider doing such thing" :-) > > 1) Would it be possible to entirely disable WAL? (something like setting a > symlink so that pg_xlog points to /dev/null, perhaps?) You can't disable WAL, but you can disable fsync. > 2) What would be the real implications of doing that? > A good chance that you lose your entire database cluster if the power fails. It's not just your tables that require WAL, it's also the system catalogs. If you were to disable it, and a system catalog became corrupt, the database would not know what to do. There's always a chance you could recover some of that data by a manual process (i.e. open up the database files in a hex editor and look for your data), but there would be no guarantee. Regards, Jeff Davis
On Mon, 2007-04-09 at 16:05 -0400, Carlos Moreno wrote: > 2) What would be the real implications of doing that? Many people ask, hence why a whole chapter of the manual is devoted to this important topic. http://developer.postgresql.org/pgdocs/postgres/wal.html -- Simon Riggs EnterpriseDB http://www.enterprisedb.com