Hello,
If the connection is open on a machine which is then downed, then any furtherI am no expert on playing around with IP addresses, but I would think this a rather dodgy option. Wouldn't connections which you appear to have open still get through, and connect to something unexpected? Dynamic DND would probably work. I cannot guarantee access to the DNS system I (or rather, my customers) are using, so this is not an option. I have therefore had to implement failover at the application level.
reads/writes would fail, and you would need to reconnect.
Is your failover a manual or automatic process?, ie, if one DB goes down, do you need to run a script manually to failover, or does this happen transparently?The problem is more ensuring that things do *not* start up unexpectedly. If the slave has suffered only a short outage, then comes back up again, it will try and restart replication. But it must not do so because it is no longer the master and its databases are now out of date. I therefore have the following features: On failover, the surviving machine is told to stop replication from the deceased, even if it returns. Machines are not set to start slaving automatically at powerup. Instead the application level checks to see if the two are in sync (by a special one-entry table incremented every time the system cold starts) and only starts the slaving process if both are at the same synch level. When the deceased machine does return, the application orders it to drop and reload the databases from the master. Once this has done, slaving can resume.
I assume that once the deceased machine returns and drops/reloads its databases, it sets the sync levels to be the same?
My theory for our network here is to have something like:I use not circular but linear replication. A->B->C->... A is write master for all tables, but B, C and D can be use as read-only copies for queries. Since I have probably a 4:1 read to write ratio, this balances quite well.
[Reader A] [Reader B] [Reader C] [Reader D]
---------- ----------
|Master A| |Master B|
|RO: fred|<<--------------------------|RW: fred|
|RW: hank|-------------------------->>|RO: hank|
---------- ----------So you have two master databases with failover, and you have any number of reader databases which sync their DBs from the appropriate RW database (which is why floating IPs would be needed I would think)
If Master A and Master B are up to date with eachother, then should one fail, surely a 'SWITCH MASTER TO xxxx' command on each of the readers would let them continue to be up to date?
Can you see any(many?) problems with this?
As you can probably tell, this is my first foray into MySQL replication...
Many thanks, Jonathan.
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