On Thu, 2007-04-19 at 15:48 -0500, Thomas F. O'Connell wrote: > "If we take a backup of the standby server's files while it is > following logs shipped from the primary, we will be able to reload > that data and restart the standby's recovery process from the last > restart point. We no longer need to keep WAL files from before the > restart point. If we need to recover, it will be faster to recover > from the incrementally updated backup than from the original base > backup." > > > I'm specifically confused about the meaning of the following phrases: > > > "backup of the standby server's files" - Which files? the files that make up the database server: - data directory - all tablespace directories > "reload that data" - What does this mean in postgres terms? copy back from wherever you put them in the first place "that data" referring to the "files that make up the db server" > "last restart point" - What is this? Wouldn't it be able to restart > from the last recovered file, which would presumably occur later than > the last restart point? No, we don't restart file-by-file. http://developer.postgresql.org/pgdocs/postgres/continuous-archiving.html#BACKUP-PITR-RECOVERY "If recovery finds a corruption in the WAL..." onwards explains the restart mechanism. It's much like checkpointing, so we don't restart from the last log file we restart from a point possibly many log files in the past. > Does this mean make a filesystem backup of the standby server's data > directory while it's stopped, and then start it again with that data > and the restricted set of WAL files needed to continue recovery? No need to stop server. Where do you read you need to do that? > I'd like to see the language here converted to words that have more > meaning in the context of postgres. I'd be happy to attempt a revision > of this section once I'm able to complete an incrementally updated > backup successfully. Feel free to provide updates that make it clearer. > Here's how I envision it playing out in practice: > > > 1. stop standby postgres server > 2. [optional] preserve data directory, remove unnecessary WAL files > 3. restart standby server step 2 only. Clearly not an optional step, since its a 1 stage process. :-) -- Simon Riggs EnterpriseDB http://www.enterprisedb.com
