On 11/29/2010 12:55 PM, Leonardo Santagada wrote:
> On Mon, Nov 29, 2010 at 5:17 PM, Chris Withers<ch...@simplistix.co.uk>  wrote:
>> Wouldn't this require zero replication lag?


>> Even if the read replicas had only a second or two delay (or spike
>> delays caused by large writes?), would there not potentially be quite
>> serious problems?


> What I think shane meant was to have clients that only read data (eg
> anonymous users) so they can read old data without causing problems
> and clients that edit content use the primary database.

Correct, although "old" means up to a few seconds old.

> Seems to be a bad way to improve performance, the only advantage I
> would see from using cache is if you somehow have logged in users that
> don't edit data and have most/all of the pages dependent on the logged
> user, for example a forum.

This strategy would be bad for a site that expects most users to log in 
and edit, such as Facebook or Twitter, but it is a proven strategy for 
forums, wikis, blogs, news sites, stores, and many other kinds of sites. 
  It is more reliable than caching, since failed caches often lead to 
cascading failures.  (See the recent Facebook outage.)

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