David E. Wheeler
david at justatheory.com
Thu Jul 25 19:25:40 UTC 2013
We have a Bucardo configuration that replicates multiple database between two data centers using multi-master replication with 4.99.7. I probably should have asked a few questions about this configuration before we rolled it out, but better late than never, I suppose. Here goes:
* In practice, for relatively static databases (say a couple thousand updates a day), and using autokick (née ping), how much lag can we expect between the two data centers? Does it mainly come down to the throughput of the network connection between them? Or should we just assume a certain amount of lag due to the overhead of Bucardo (NOTIFY timing, listening between NOTIFYs, copy performance, etc.)?
* If we want to shut down one of the servers for maintenance, we will point all traffic at the other box. Is there an easy way to tell when all the databases on the node to be shut down have had all their data synced over? Or would I just have to write a scrip to check all of the delta table row counts until they are all zero?
* What experiences have you had with Bucardo multi-master replication where app servers randomly write to any of the masters, without any session affinity or similar? In practice, are there any problems with a user writing data and then not seeing it show up, because one request goes to one server to write, then reads from the other before the sync finishes? Does this happen occasionally? Rarely? Often?
Thank you for sharing your experience and knowledge!
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