Re: Update low-level backup documentation to match actual behavior

On Wed, Aug 30, 2017 at 8:02 PM, David Steele <david(at)pgmasters(dot)net> wrote:
> On 8/29/17 9:44 PM, Michael Paquier wrote:
>> On Tue, Aug 29, 2017 at 10:59 PM, David Steele <david(at)pgmasters(dot)net> wrote:
>>>
>>> Attached is the 9.6 patch. It required a bit more work in func.sgml
>>> than I was expecting so have a close look at that. The rest was mostly
>>> removing irrelevant hunks.
>>
>> + switch to the next WAL segment. On a standby, it is not possible to
>> + automatically switch WAL segments, so you may wish to run
>> + <function>pg_switch_wal</function> on the primary to perform a manual
>> + switch. The reason for the switch is to arrange for
>> [...]
>> + WAL segments have been archived. If write activity on the primary
>> is low, it
>> + may be useful to run <function>pg_switch_wal</> on the primary in order to
>> + trigger an immediate segment switch of the last required WAL
>> It seems to me that both portions are wrong. There is no archiving
>> wait on standbys for 9.6, and
> I think its clearly stated here that pg_stop_backup() does not wait for
> WAL to archive on a standby. Even, it is very important for the backup
> routine to make sure that all the WAL *is* archived.

Yes, it seems that I somewhat missed the "on the primary portion"
during the first read of the patch.

>> pg_stop_backup triggers by itself the
>> segment switch, so saying that enforcing pg_switch_wal on the primary
>> is moot.
>
> pg_stop_backup() does not perform a WAL switch on the standby which is
> what this sentence is referring to. I have separated this section out
> into a new paragraph to (hopefully) make it clearer.
>
>> pg_switch_xlog has been renamed to pg_switch_wal in PG10, so
>> the former name applies.
>
> Whoops!
>
> New patch is attached.

Thanks for the new version. This looks fine to me.
--
Michael