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Re: Master database crashed
Posted by: Rick James
Date: November 30, 2011 10:23AM

The situation:
1. Master and slave are working fine.
2. Network goes down (both servers are otherwise working fine). During this time, the Master is writing things to its "binlog", but the Slave is not receiving copies of it (yet).
3. The Master crashes before the network recovers.

Now what?

Case 1: If you can get the network, the Master, and the Slave all running at the same time, the pending stuff in the binlog will automatically be copied to the Slave's relay log.

Case 2: If the Master's disk is unrecoverable, then you have lost the only copy of the pending replication statements.

If this double-failure is of serious concern, consider having another Slave, and have it "close" to the Master so that it is less likely to fail due to a network problem.

(I have dealt with international Master-Slave situations for a decade. I don't recall a case of both the network and the Master failing at the same time.)

At some point, you have to say "We will protect the system from any 'single failure', and make the likelihood of single failures low enough so that the odds of a 'double failure' can be ignored.

You can throw money at each possible failure point. (or, perhaps, "waste money".)
* If disk drive failure is a serious concern (and I don't think that is realistic these days), RAID can virtually eliminate that from bringing down the server.
* Servers -- more Slaves
* Networks -- separate access paths to separate slaves

Software corruption (eg, an accidental DROP TABLE) -- that is a different kettle of fish.

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