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#1 (**permalink**) 04-09-2008, 03:13 PM

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/pgdo...-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

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#2 (**permalink**) 04-09-2008, 03:14 PM

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/pgdo...es/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

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#3 (**permalink**) 04-09-2008, 11:21 PM

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/pgdo...-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. +

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Re: [DOCS] Incrementally Updated Backups: Docs Clarification