Chuck Rolke created DISPATCH-525:
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Summary: What are proper names and units for protocol
configuration settings?
Key: DISPATCH-525
URL: https://issues.apache.org/jira/browse/DISPATCH-525
Project: Qpid Dispatch
Issue Type: Improvement
Components: Management Agent
Affects Versions: 0.7.0
Reporter: Chuck Rolke
Several settings are available in configuration objects that are used in AMQP
negotiations with clients. Some of them are confusing as they exist now and
could be redefined to make their understanding and usage easier for end users.
The same settings are defined for Router Listener and Connector and for Policy
Vhost objects.
||Setting||Units||Range||
|maxFrameSize|octets|uint|
|maxSessions|sessions|uint16|
|maxSessionWindow|octets|uint|
|maxMessageSize *not implemented*|octets|uint|
|linkCapacity|messages|integer|
These settings have to work in cooperation with the proton engine interface.
h2. maxFrameSize
This setting is straightforward. The range is 0..ULONG_MAX.
Using octets is fine. This value must be 512 or larger per AMQP spec.
h4. Proposal
Leave this setting unchanged.
h2. maxSessions
This setting is in units of 'sessions'. The acceptable values are in the range
1..65536.
The number given in the configuration is one larger than the value used by AMQP
and proton. In AMQP the channel-max value of an Open is the largest channel
number that can be used. So a channel-max of 0 allows one session, and a value
of 1 allows two sessions, and so on.
I prefer to have the spec values be equal to the number of sessions allowed.
* Dispatch code subtracts one from the specified value and puts it into proton
channel-max.
* A value of zero in the spec can be disallowed or it can mean some default
value.
h4. Proposal
Leave this setting unchanged.
h2. maxSessionWindow
This setting is in octets. The range is 0..ULONG_MAX with a minimum of
max-frame-size octets.
This setting is slightly confusing as the specification is in octets. Then that
value of octets is passed to proton in pn_session_set_incoming_capacity. Proton
divides the incoming_capacity by the max-frame-size and uses the result in a
Begin incoming-window. The incoming-window then is measured in transfer frames.
For example:
* maxFrameSize = 65,536.
* maxSessionWindow = 1,000,000.
Dividing (1000000 / 65536) = 15 frames. The 15 is used in the
Begin/incoming-window field during negotiation with the peer.
A user expecting to have about a megabyte of buffering on the session might be
surprised to find all the buffering consumed by 15 100-byte transfer frames.
h4. Proposal
* Rename this setting to *maxSessionFrames*.
* Change this setting's units of 'transfer frame'. Then the value sent to
proton in incoming_capacity would be calculated by (maxSessionFrames *
maxFrameSize). The value of maxSessionFrames would then appear in the
Begin/incoming-window field.
h2. maxMessageSize
This setting is in octets. The range is 0..ULONG_MAX.
This setting is TBD. No interface in proton engine is available to change it.
If this value is zero or, more typically, not set then there is no maximum
message size.
h4. Proposal
Leave this setting unchanged.
h2. linkCapacity
This setting is in transfer frames. The range is 0..LONG_MAX.
This setting defines how much credit is issued on links created on a
connection. It specifies how many transfers can be in-flight concurrently for
each link.
This setting is for Listener and Connector objects only. It is not defined for
Policy Vhost objects.
h4. Proposal
* Leave the units and current meaning of this setting unchanged.
* Add this value to the Policy Vhost settings so that it may be overridden on a
Vhost Usergroup basis.
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