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From: Albe Laurenz <[email protected]>
To: Michael Paquier  *EXTERN* <[email protected]>
To: Kaushal Shriyan <[email protected]>
Cc: Torsten Förtsch *EXTERN* <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: PG replication across DataCenters
Date: Fri, 22 Nov 2013 14:46:00 +0000
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Michael Paquier wrote:
> On Fri, Nov 22, 2013 at 10:03 PM, Kaushal Shriyan <[email protected]> wrote:
>> I am not sure i understand the difference between async and sync replication
>> and on what scenarios i should use async or sync replication. Does it mean
>> if it is within same DC then sync replication is the best and if it is
>> across DC replication async is better than sync. Please help me understand.

> In the case of synchronous replication, master node waits for the
> confirmation that a given transaction has committed on slave side
> before committing itself. This wait period can cause some delay, hence
> it is preferable to use sync replication with nodes that far from each
> other.

I am sure that you wanted to say
"with nodes *not* that far from each other".

Basically, you have to choose between these options:
- Slow down processing, but don't lose a transaction on failover
  (this would be synchronous, nodes close to each other)
- Replicate over longer distances, but possibly lose some
  transactions on failover (that would be asynchronous).

Yours,
Laurenz Albe

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