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Q1: How many can I extend Cluster DB?
The number of the maximums of Cluster DB is 128. If you need more Cluster DBs , you can also change a maximum value. However, if Cluster DB server is extended, the load of a replication server and a load balance server will increase. You had better extend it only the required minimum number to your system.
Q2: Is it possible to run a replication server and Cluster DB server on one machine?
It is possible when you use pgcluster-1.0.6cv4 or later. But probably, in the system which needs a load balance and a high-availability, such system composition will be dangerous. If a load balance or a high-availability is required in your system, you should run a replication server independently.
Q3: Is it necessary to execute the VACUUM command for every Cluster DB?
When you execute the VACUUM command to one Cluster DB, a command will be reproduced and will be executed in all the Cluster DBs. If you execute the VACUUM FULL command to Cluster DB, the VACUUM FULL command is executed in all the Cluster DBs. Probably, it will be better to have stopped the system and to execute one command at a time, when you want to execute the VACUUM FULL command.
Q4: Is a backup command replicated?
PGCluster replicates neither pg_dump nor the COPY (TO) command.
Q5: Does PGCluster support the latest version of PostgreSQL?
PGCluster-1.1.0 are made based on PostgreSQL7.4.6. I am going to make PGCluster Which is based on PostgreSQL8.0 after next version.