[rabbitmq-discuss] New Persister merged into default

Matthias Radestock matthias at rabbitmq.com
Wed Aug 11 07:18:49 BST 2010

Srijanani Srinivasan wrote:
> Please correct me if i am wrong, i believe that currently the messages 
> are in the queue are loaded in the memory, and if they are marked 
> persistent, any time the consumer stops consuming messages or 
> other scenarios the messages are written to the disk and retrieved later 
> when needed.

Not quite. In the old/current persister, messages marked as persistent 
that are sent to durable queues are written to disk straight away 
(except for various buffering stages). They are *also* kept in memory, 
like all messages. Hence with the old persister rabbit requires enough 
memory to hold all messages, persistent or not. By contrast, the new 
persister can page messages to/from disk in response to changing memory 
conditions. This happens regardless of whether the messages are marked 
persistent. So the "new persister" is not just about message 
persistence, but message storage in general. Memory becomes an optional 
extra, though it's quite handy to have some :)



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