Thread: Re: [DOCS] Incrementally Updated Backups: Docs Clarification
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
On Apr 25, 2007, at 9:42 AM, Simon Riggs wrote: > 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 Well, this conversation made things a lot clearer, but I'm not sure (yet) how to patch the docs. It seems like the original version is written in general terms, whereas what our Q&A produces here is very postgres-specific. I'll see if I can produce a version that would be add clarity (for me). -- Thomas F. O'Connell optimizing modern web applications : for search engines, for usability, and for performance : http://o.ptimized.com/ 615-260-0005
I have updated the docs by changing a few words, patch attached. --------------------------------------------------------------------------- Simon Riggs wrote: > 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 > > > > ---------------------------(end of broadcast)--------------------------- > TIP 3: Have you checked our extensive FAQ? > > http://www.postgresql.org/docs/faq -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://postgres.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + Index: doc/src/sgml/backup.sgml =================================================================== RCS file: /cvsroot/pgsql/doc/src/sgml/backup.sgml,v retrieving revision 2.114 diff -c -c -r2.114 backup.sgml *** doc/src/sgml/backup.sgml 13 Feb 2008 22:44:06 -0000 2.114 --- doc/src/sgml/backup.sgml 7 Mar 2008 01:40:26 -0000 *************** *** 1814,1820 **** </para> <para> ! 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. --- 1814,1820 ---- </para> <para> ! If we take a backup of the standby server's data directory while it is processing 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.