[Pgpool-general] 3 Servers needed?

[Damian Lubosch]

Jacinta Carvalho wrote:

>Hello
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>

Hi!

First of all, thanks for the fast and detailed answer :-)

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>[...]
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>You want some kind of high availability. Some solutions :
>- pgpool on both servers but you need heartbeat. It would be the best
>solution using only two servers. I haven't tested yet.
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Actually, I won't use heartbeat because it doesn't run on netbsd, but
instead I will use ucarp, which switches "real" ip addresses to
"virtual" ip-addresses and works fine on my machine. It also allows to
execute further commands.

>- pgpool on both servers for replication, and a high availability
>system (LVS) that forwards requests to the running server.
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I won't use LVS, since netbsd is my system. But I read about it and it
sounds very interesting for other projects maybe.

>What you want can't be made with 3 servers. If pgpool runs on a server
>and sends requests to two other servers, the pgpool server is a
>weakness : total failure of this server means no possible connection
>to the database.
>
>Let's take 4 servers. LVS runs on two of them, pgpool and postgreSQL
>run on the two other ones (pgpool AND postgres run on each server).
>The requests are made to a virtual address thanks to LVS. On the LVS
>system, you define a primary and a secondary pgpool server. If the
>primary server is up, pgpool will get the requests and send them to
>both database servers. If the primary server is down, as pgpool is
>also running on the secondary server, it will get and forward the
>requests to both databases servers. This solution works.
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>Running LVS, pgpool and Postgres on the same two servers would be an
>implementation of the first solution using only two servers.
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>It's a bit hard to explain, but I hope it will help...
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Thank you very much. It helped me a lot.

>Best regards.
>--
>Jacinta Carvalho
>jacinta.carvalho at gmail.com
>____________________________
>
Bye,
Damian.