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    <p>I'm not a specialist but the <strong>read/write master database and read-only slaves</strong> pattern is a "common" pattern, especially for big applications doing mostly read accesses or data warehouses:</p> <ul> <li>it allows to scale (you add more read-only slaves if required)</li> <li>it allows to tune the databases differently (for either efficient reads or efficient writes)</li> </ul> <blockquote> <p>What would be a good resource to find out more about this architecture?</p> </blockquote> <p>There are good resources available on the Internet. For example:</p> <ul> <li><a href="http://highscalability.com/" rel="nofollow noreferrer">Highscalability.com</a> has good examples (e.g. <a href="http://highscalability.com/wikimedia-architecture" rel="nofollow noreferrer">Wikimedia architecture</a>, the <a href="http://highscalability.com/blog/category/master-slave" rel="nofollow noreferrer">master-slave</a> category,...)</li> <li><a href="http://www.slideshare.net/directi/handling-data-in-mega-scale-systems" rel="nofollow noreferrer">Handling Data in Mega Scale Systems</a> (starting from slide 29)</li> <li><a href="http://uni-svishtov.academia.edu/AsenBozhikov/Papers/82526/MySQL-Scale-Out-approach-for-better-performance-and-scalability-as-a-key-factor-for-Wikipedia%E2%80%99s-growth" rel="nofollow noreferrer">MySQL Scale-Out approach for better performance and scalability as a key factor for Wikipedia’s growth</a></li> <li><a href="http://www.postgresql.org/docs/8.2/static/high-availability.html" rel="nofollow noreferrer">Chapter 24. High Availability and Load Balancing</a> in PostgreSQL documentation</li> <li><a href="http://dev.mysql.com/doc/refman/5.1/en/replication.html" rel="nofollow noreferrer">Chapter 16. Replication</a> in MySQL documentation</li> <li><a href="http://www.google.com/search?q=read%2Fwrite+master+database+and+read-only+slaves" rel="nofollow noreferrer">http://www.google.com/search?q=read%2Fwrite+master+database+and+read-only+slaves</a></li> </ul> <blockquote> <p>Is it just a question of replicating between two identical schemas, or would your schemas differ depending on the operations, would normalisation vary too?</p> </blockquote> <p>I'm not sure - I'm eager to read answers from experts - but I think the schemas are identical in traditional replication scenari (the tuning may be different though). Maybe people are doing more exotic things but I wonder if they rely on database replication in that case, it sounds more like "real-time ETL".</p> <blockquote> <p>How do you insure that data written to one database is immediately available for reading from the second?</p> </blockquote> <p>I guess you would need <em>synchronous replication</em> for that (which is of course slower than asynchronous). While some databases do support this mode, not all do AFAIK. But have a look at <a href="https://serverfault.com/questions/58829/how-to-keep-multiple-read-write-db-servers-in-sync">this answer</a> or <a href="https://stackoverflow.com/questions/12946/database-replication-2-servers-master-database-and-the-2nd-is-read-only">this one</a> for SQL Server.</p>
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    1. POHow would I implement separate databases for reading and writing operations?
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    1. POHow would I implement separate databases for reading and writing operations?
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    1. CO@Pascal Thivent ~ Wouldn't this be http://en.wikipedia.org/wiki/Command-query_separation
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    2. CO@drachenstern: I'm not sure CQS implies anything about the way you store data. But thanks, it's a very interesting link.
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    3. CO@Pascal Thivent ~ I was thinking more about the reference of having a pub/sub sync arch between the two. I was also thinking that article had images when I blind linked to it: http://www.udidahan.com/2008/08/11/command-query-separation-and-soa/
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