On Thu, 2006-03-02 at 16:38 -0600, Thomas F. O'Connell wrote: > I'm administering a database that is not immediately a good candidate > for replication via Slony. As an interim solution, I'd like to give > PITR a shot. The primary goal is to have a failover scenario that > allows for recovery within a window that's much smaller than it would > be if the only option were the output of the previous night's > pg_dump, and the need has arisen jointly with the fact that pg_dump > has become an unwieldy process on this database. > > Here's the main question: Is it possible to replay logs continuously > against a database that has already been recovered? The documentation > only covers the scenario of full recovery from scratch, and I'm > wondering if this is because this is the only scenario possible with > the current level of PITR functionality. > Ideally, I'd be able to take a base backup of a production system, > copy it to a remote system, which is also the repository for segment > files generated by archive_command, and complete the recovery process > outlined in the docs. From that point, it would make sense to me that > I should be able to continuously replay WAL files against the new > database (possibly as soon as archive_command generates a new one) > without having to purge my data directory. Is that a reasonable > assumption? Yes, it was designed to be able to do this. > If so, then I need to know more about which steps to use from the > recovery scenario presented in the docs and how to identify the state > in which a given segment file exists. > For instance, it's not > immediately clear from the docs what happens to the segment files > after recovery_command runs during the recovery scenario. It says > those segments are copied from the archive directory, but then what? > Are they recycled as in a basic postgres installation? They overwrite each other, thus avoiding a build up of logs. It is designed to support "infinite" recovery. > Also, if this system eventually works as I expect it might be able > to, would there ever be a reason to redo it from scratch (i.e., is > one base backup sufficient ad infinitum)? As long as you've read the documented caveats there are no design limitations...but I would restart from a base backup weekly, to be sure. It's all about certainty after all. Best Regards, Simon Riggs
