On 02/27/11 4:48 AM, Jasmin Dizdarevic wrote:
I have to build a load balanced pg-cluster and I wanted...
master-master doesn't work real well with databases, especially ones like postgres that are optimized for a high level of concurrency and transactional integrity.
on proper hardware, postgres can run quite high transactional volumes on a single server. If high availability is a requirement, you can run a 2nd server as a standby slave using either postgres streaming replication, or drbd style block replication, or another such similar technique.
you -can- distribute read accesses between a master and a slave server via things like pgpool2, where all inserts, updates, DDL changes, etc are made to the master server, but reads are done to either. note you do NOT want to use block level replication like drbd for this as the drbd slave can not be actively mounted, nor could the slave instance of postgres be aware of changes to the underlying storage, rather you would use the streaming replication built into postgresql 9.0. another approach is to use the master server for all OLTP type accesses, and the hot standby server for more complex long running OLAP queries for reporting, etc. in case of master failure, the slave becomes the new master, and you shut down the presumably less important OLAP operations until such time as a new slave can be deployed.
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