I encountered a small issue when I run the script in the old-primary. The
"SELECT pg_start_backup...." part of the script will fail since the
postgres service has been stopped. Is this error meant to happen?
On Fri, Feb 18, 2011 at 11:55 AM, Dean Gibson (DB Administrator) <
postgre...@ultimeth.com> wrote:
> On 2011-02-17 17:43, Selva manickaraja wrote:
>
> Does this mean the fail-over will not be auto the moment the primary DB or
> Server goes down? Does it require for us to manually intervene to introduce
> the trigger_file?
>
>
> Yes, and yes.
>
> I depends upon the installation, as to how to detect that that the primary
> has gone down (eg, lose network connection for how long?). Therefore, it is
> left to the sysadmin (that's you and me) to write external procedures to
> detect when it is time to fail-over, and write an appropriate automated
> script to create the trigger file (or do it manually). I do it manually,
> because I have multiple slaves and the procedures are slightly more complex
> than for just one slave.
>
> Setting up the configuration files is pretty trivial:
>
> 1. On each slave, create a recovery.conf that points to the primary.
> 2. Optionally, on the primary, create a recovery.done (note the different
> extension) that points to whichever slave you plan on later switching to a
> primary in case of a fail-over.
>
> In the case of the failure of the primary:
>
> 1. Make sure the primary will not come back up (yet).
> 2. Create the trigger file (which triggers the switch) on whatever slave
> you wish to become the new primary.
> 3. If you have only one slave, you are done. If you have more than one
> slave, you will need to (on each other slave):
> 3.a. Stop the slave.
> 3.b. Edit the recovery.conf file to point to the new primary.
> 3.c. Restart the slave.
> 3.d. If the slave does not properly sync to the new primary, you may have
> to (ugh) run the script below to resynchronize the slave to the new primary.
>
> When you are ready to have the old primary become a new slave, resync the
> data on the old primary to the new primary (I use the following script on
> the old primary):
>
> service postgresql stop
> {
> cat <<-EOF
> SELECT pg_start_backup( '$(date
> --iso-8601)', true );
> \! rsync -vaz --delete
> new.primary.hostname:$PGDATA/ $PGDATA/
> SELECT pg_stop_backup();
> EOF
> } | psql -e template1 postgres
> mv $PGDATA/recovery.{done,conf}
> service postgresql start
>
> Presto! Your old primary is now back up as a slave.
>
>
> On Fri, Feb 18, 2011 at 1:17 AM, Dean Gibson (DB Administrator) <
> postgre...@ultimeth.com> wrote:
>
>> On 2011-02-16 18:10, Selva manickaraja wrote:
>>
>>> We tried setting the trigger file for fail-over purpose. But we just
>>> can't understand how it works. Each time the secondary is started the
>>> trigger file is removed. How can we introduce auto fail-over is this
>>> happens?
>>>
>>> Thank you. Regards, Selvam
>>>
>>
>> That's exactly what is supposed to happen. You will also find that the
>> recovery.conf file gets renamed when the trigger file is created by you (and
>> then is promptly deleted by PostgreSQL).
>>
>>
>> Don't create the trigger file until you want the hot-standby server to
>> switch roles and become the primary server (and thusly accept DB change
>> requests).
>>
>
>
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>
