Re: More subtle issues with cascading replication over timeline switches

On Friday, January 18, 2013 5:27 PM Heikki Linnakangas wrote:


> Indeed, looking at the pg_xlog, it's not there (I did a couple of extra 
> timeline switches:

> ~/pgsql.master$ ls -l data-master/pg_xlog/
> total 131084
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000010000000000000001
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000010000000000000002
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000010000000000000003
> -rw------- 1 heikki heikki       41 Jan 18 13:38 00000002.history
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000020000000000000003
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000020000000000000004
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000020000000000000005
> -rw------- 1 heikki heikki       83 Jan 18 13:38 00000003.history
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000030000000000000005
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000030000000000000006
> drwx------ 2 heikki heikki     4096 Jan 18 13:38 archive_status
> ~/pgsql.master$ ls -l data-standbyB/pg_xlog/
> total 81928
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000010000000000000001
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000010000000000000002
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000020000000000000003
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000020000000000000004
> -rw------- 1 heikki heikki       83 Jan 18 13:38 00000003.history
> -rw------- 1 heikki heikki 16777216 Jan 18 13:38 000000030000000000000005
> drwx------ 2 heikki heikki     4096 Jan 18 13:38 archive_status

> This can be thought of as another variant of the same issue that was 
> fixed by commit 60df192aea0e6458f20301546e11f7673c102101. When standby B 
> scans for the latest timeline, it finds it to be 3, and it reads the 
> timeline history file for 3. After that patch, it also saves it in 
> pg_xlog. It doesn't save the timeline history file for timeline 2, 
> because that's included in the history of timeline 3. However, when 
> standby C connects, it will try to fetch all the history files that it 
> doesn't have, including 00000002.history, which throws the error.

  Is the file 00000002.history really required by standby C for any useful purpose?
  Can we think of change in current design such that when standby C connects, even if some old history file (like 00000002.history)
  is not present, it ignores the same and continue.

With Regards,
Amit Kapila.