Can you use the txlogger for hot-backup in reverse?

hot-backup from server 1 to server 2
server 1 fails
log on to server 2 and reverse txlogger, so hot-backup goes from server
2 to server 1
writes queue up on server 2 since server 1 is down
let everyone work off server 2
fix server 1
log off everyone from server 2
receive writes from server 2 to server 1
reverse txlogger so hot-backup is from server 1 to server 2 again
start using server 1 again

Is this scenario reasonable? Has anyone tried it? What problems do you
run into?

Herb Rubin
Pathfinders Software

Herb,

It should work pretty much just like that.

If server 2 is as fast as server 1, they shouldn't be any problem with
transaction lag, so all you lose is what's currently in memory when server 1
crashes. While still at PS/RD, I saw at least three sites using hot backup
and doing 1000s of transactions a day.

turn on txlogging on server 2 when it becomes the master. either
save/restore server 1 once it's running again, or use (iirc) txlog-restore
to restore new transactions made on server 2.

Once you are back on server 1, you should do a full save/restore to slave
and re-sync

Problems can arise if you let anyone onto server 2 while server 1 is still
the master. Don't let the files get out of sync (create new ones on S2;
chng items directly on S2).

Mark Brown


<herbr (AT) pfinders (DOT) com> wrote

Thanks Mark. Its always good to hear from you.

Do you think if we
1) control users logging in by changing all passwords and forcing
logoffs
2) and don't create any new files
3) Watch the txlogger for flushing its queue.
4) ensuring we reverse the txlogger direction before letting users back
on

we can safely switch RS6000's back and forth without a full restore?

Yes.

Those are exactly the things I would monitor. As long as the txlog queue
flushes fast enough there's not much danger of losing data.

Also, remember where you start hot-backup.master and hot-backup.slave is
what determines which is which. Theoretically, you could run on server 1,
hb to server 2 which does hb to server 3 etc. At any point in time, any
connection between any two machines can be broken, at which point it simply
stashes in the txlog.

It's just a juggling act. As I recall, you were always pretty good at that.

Still playing the blues in seedy bars? With arthritis, I can't make all the
chords (like I ever could), so I'm playing more slide guitar now.

Mark


<herbr (AT) pfinders (DOT) com> wrote

I still play guitar and bass. I learned Blackbird, so that's fun.

I recently bought an SWR Bass head (350 watts) to rock the neighbors.
Kinda reminds me of Back To The Future...