More reserved queue attributes

https://blueprints.launchpad.net/zaqar/+spec/more-reserved-queue-attributes

Currently Zaqar supports setting metadata/attributes when user creating queue. However, the metadata/attributes are not used very much by Zaqar itself. Now we only support ‘_flavor’ but it would be nice if we can support more attributes to make the queue more flexible.

Problem description

Now Zaqar supports max_messages_post_size, default_message_ttl, default_claim_ttl and default_claim_grace. All of them defined in Zaqar’s configuration file. That means it’s global setting, all queues have to share the same configurations. It’s not really flexible from the end user perspective. So it would be nice if we can let end user set them and use the default value in configuration file if they are not defined.

Proposed change

The changes are not complicated, which may change two actions: Post messages and create claim for a queue.

  1. Post Message: At line stable/liberty/zaqar/transport/wsgi/v2_0/messages.py#L182, we need to get the queue’s metadata so as to get the queue’s max_messages_post_size and ttl defined by user when creating the queue. If those aren’t exist, then just use the global configuration defined in configuration file.
  2. Create Claim: Similar thing like above, we need to get the queue’s metadata at line stable/liberty/zaqar/transport/wsgi/v2_0/claims.py#L81 and then use that to do the check.

Drawbacks

It may introduce a tiny performance impact for message posting and claim creating. For example, instead of just checking if the queue is existing or not, Zaqar need to get the queue’s metadata so that to get those attributes. But actually, we can use ‘get_metadata’ replace ‘exists’ to check if the queue exist or not, and they’re calling the same collection.find_one() method, so technically, there is no performance impact.

Alternatives

Just keep current way, let all the queues share the same configurations.

Implementation

Assignee(s)

Primary assignee:
flwang (flwang@catalyst.net.nz)

Work Items

  1. Support max_messages_size and ttl as queue attributes
  2. Support claim_ttl and claim_grace as queue attributes

Dependencies

N/A

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