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Load balance Three Postgresql database (Primary, Secondery1 and Secondery2) Servers

Posted on 2014-07-24
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Last Modified: 2014-07-27
Hi Experts,

I have somewhat large Postgresql database to manage and it's about 10GB after I made a dump and I believe it will take about 100GB space after it's populated on a hard disk. Currently I have implemented this on a Standby hot replication cluster. Two basic modules are running in this application and some reporting modules are directly connecting to the Secondary node(read only) and still there some SELECT queries coming in to Primary node(read/write) too.

Pgbouncer has implemented on both of these two database servers and currently operates on Transaction mode.  

I get too high I/O rate and Processing rates ( %I/O wait is around 15 ~ 20, Load leverage is around 8 ~ 10) in the peak times. (these two databases are running on SSD with 8 cores of 2.5 Ghz, two Blades, Ubuntu 12.04 server 64bit )

So I'm planning to add third read only server and implement a mechanism to balance the load across these three DB servers. Example, filter all the read requests on secondery1, secondery2  and write requests on the Primary.

Did any one tried this with pgpool-II, or what is your valuable recommendation on such a situation ?

Thanks a lot for your time !
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Question by:Shakthi777
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by:lcohan
lcohan earned 166 total points
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"Two basic modules are running in this application and some reporting modules are directly connecting to the Secondary node(read only) and still there some SELECT queries coming in to Primary node(read/write) too. "

In my opinion it would be better to direct the traffic from the application to the desired instance and not from the backend database servers. In other words the app should have 2/3 connection strings (and app pools) to direct the queries against the desired "node" for the desired purpose.
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Daniel Wilson earned 334 total points
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Another option is pl/Proxy.
https://wiki.postgresql.org/wiki/PL/Proxy

That is the solution Hannu Krosing developed to scale Postgres for Skype.

I haven't yet implemented a cluster in PostgreSQL, but PL/Proxy is the tool I expect to use ... later this year.
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by:Shakthi777
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I really wanted to thank for all your prompt responses,

#lcohan
This applications has implemented with a single connections string, any good approach on separating those ?

#Daniel Wilson
Partitioning is another option it's seems ?
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by:Daniel Wilson
Daniel Wilson earned 334 total points
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PL/Proxy involves a partitioning / sharding scheme.  The application knows nothing of the sharding.  It simply talks to the proxy.  The proxy knows which shard to contact .
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by:Shakthi777
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Thanks for the valuable comments !
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