Unnecessary DescribeWorkflowExecution calls when accessing closed_at

[awendt]

I'm trying to find specific workflow executions by tag:

> workflow_executions = swf.domains[domain_name].workflow_executions.closed_after(Time.now-1.hour).tagged(tag_name)
#=> <AWS::SimpleWorkflow::WorkflowExecutionCollection>
> workflow_executions.each {|ex| puts ex.started_at}
AWS SimpleWorkflow 200 0.39347 0 retries] list_closed_workflow_executions(…)
2013-10-22 08:04:41 +0200
2013-10-22 08:04:46 +0200
=> nil

So far, so good. Now I'd like to access not only started_at, but also closed_at:

> workflow_executions = swf.domains[domain_name].workflow_executions.closed_after(Time.now-1.hour).tagged(tag_name)
#=> <AWS::SimpleWorkflow::WorkflowExecutionCollection>
> workflow_executions.each {|ex| puts ex.started_at; puts ex.closed_at}
[AWS SimpleWorkflow 200 0.168692 0 retries] list_closed_workflow_executions(…)
[AWS SimpleWorkflow 200 0.105952 0 retries] describe_workflow_execution(…)
[AWS SimpleWorkflow 200 0.190124 0 retries] describe_workflow_execution(…)
2013-10-22 08:04:41 +0200
2013-10-22 08:04:46 +0200
=> nil

That means the SDK makes another call to the DescribeWorkflowExecution API for every workflow execution just because I'm accessing closed_at of that workflow execution.

This is unnecessary because ListClosedWorkflowExecutions already returns closeTimestamp in addition to startTimestamp.

AFAICS, the same information for n workflow executions can be obtained in 1 call instead of n+1 calls.

Am I missing something here?

[trevorrowe]

The SDK is only holding onto static attributes. Calling #closed_after on a workflow execution will trigger a new request every time to see if the value has updated service side. This is sub-optimal for tight loops like you have above.

You can work around this by enabling memoization:

AWS.memoize do
  # only one request required
  workflow_executions.each {|ex| puts ex.started_at; puts ex.closed_at}
end

All attributes are held inside a memoize block. The block indicates it is okay to cache non-static attributes within a given scope. I'm a not fan of this and we will remove the need to use memoize blocks in v2 of the SDK.

[awendt]

@trevorrowe Thanks for the quick response. And thanks for clarifying that you're not a fan of this, Github sent me an e-mail with a comment that didn't make sense, I guess that was before an edit :)

Anyway, thanks for pointing me to AWS.memoize. I wasn't aware that closeTimestamp could be updated.

[trevorrowe]

It can't be updated or specified, but it can go from nil, which means not closed to an actual timestamp. Static attributes are those like a resource identifier or a creation timestamp that never change.

I'm going to close this issue for now. I hope this helps.