Re: Sync Rep: First Thoughts on Code

Hi, thanks for the comment!

On Mon, Dec 8, 2008 at 11:04 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> > Could we start with pictures and some descriptions first, so we know
>> > we're on the right track? I foresee no coding issues.
>> >
>> > My understanding is that we start with a normal log shipping
>> > architecture, then we switch into continuous recovery mode. So we do use
>> > pg_standby at beginning, but then it gets turned off.
>>
>> Yes, I also understand so. Updated sequence pictures are on wiki
>> as per usual. Please see P3, 4.
>> http://wiki.postgresql.org/wiki/NTT%27s_Development_Projects#Detailed_Design
>
> p.6 looks good.
>
> But what is p.7? It's even more complex than the original. Forgive me,
> but I don't understand that. Can you explain?

p.7 shows one of the system configuration examples. Some people don't
want to share an archive between two servers would probably choose
this configuration, I think.

If archive is not shared, some WAL files before replication starts would not
be copied automatically from the primary to standby. So, we have to copy
them by hand or using clusterware ..etc. This is what p.7 shows. If archive
is shared, archiver on the primary would copy them automatically (p.6).

>
> What is the procedure if the standby shuts down, for example if we wish
> to restart server to change a parameter?

Stop postgres by using immediate shutdown, and start postgres from an
existing database cluster directory. When restarting postgres, if there are
one or more archives, we also need to copy the WAL files after stopping
replication before restarting replication.

> Or to reboot the system it is
> on. Does the primary switch back to writing files to archive?

I assume that the primary always writes files to archive, that is, basically
the primary doesn't switch to non-archiving mode. Of course, if archiving
is disabled on the primary in any reason when restarting standby, the
primary need to switch back.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center