Thomas Kellerer wrote:
The manual lists three possible solutions to HA: shared disk failover, file system replication and Warm/Hot Standby. I'm not an admin (nor a DBA), so my question might sound a bit stupid: from my point of view solutions using shared disk failover of file system replication seem to be more reliable in terms of how much data can get lost (and possibly the switch over lag)
Yes, but if you try you'll discover that actually getting any shared disk or file system replication solution setup so that you really do achieve less failover loss than the file shipping approach will be expensive, complicated, fragile in its own way, and just generally a pain to pull off. The fundamental problem with shared storage for example is how to keep a note that's failed from try to reassume being the master when it comes back. Doing that well requires hardware support aimed at that specific use case. Meanwhile, file shipping for Warm Standby use requires nothing special at all except some modest software setup. It's comparatively simple to setup, validate, and keep going on any hardware capable of running the database. This is why shared storage and the like isn't the only obvious solution even though it's technically capable of losing less transactions; you'll discover that keeping from losing that last little bit of data when there's a crash turns out to be quite expensive. Whether it worth it or not depends on the value of your data and whether it can be retained at some higher level when this happens instead.
-- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support greg@xxxxxxxxxxxxxxx www.2ndQuadrant.us -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
