[rabbitmq-discuss] RabbitMQ-C library: channel_max

Simon MacMullen simon at rabbitmq.com
Wed Oct 26 10:28:32 BST 2011

On 25/10/11 23:25, Pieter de Zwart wrote:
> Dumb question alert, sorry. In the rabbitmq-c library, there are a few
> parameters to the amqp_login function that confuse me: channel_max and
> frame_max. Are these essentially the global QOS settings (how many
> channels can be on this connection, 0 being unlimited AND maximum window
> frame size, within which the client will try to tune the connection)?

No, not at all.

See http://www.rabbitmq.com/amqp-0-9-1-reference.html#connection.tune

frame_max is the maximum AMQP frame size the client should accept when 
negotiating a frame size with the server. Zero is unlimited.

channel_max is the maximum number of channels per connection that the 
client will use. Zero is unlimited.

RabbitMQ really doesn't care much about this, but conceivably other 
server implementations might require your client to agree to a low value.

> What are legitimate values for these? Should I expose them in the PHP
> extension, and allow people to change them prior to connecting?

Depends how completist you feel. Tuning frame_max can make differences 
to throughput in some situations. channel_max is not very interesting 
when connecting to RabbitMQ.

Cheers, Simon
Simon MacMullen
RabbitMQ, VMware

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