Fetch Interval
Key Fetch Interval in ExCfgLvFd refers to the minimum time interval in milliseconds between two successive fetch requests to the live feeds provider's server.
This number is different from the Takt of the update process in the sense that it applies to the chain of requests being raised automatically by Deriscope in the process of assembling the feeds for all tickers at each takt iteration.
That chain consists of a single request only if all tickets can be processed by the server in a single step.
For example, Yahoo can process up to 200 tickets at a time, so that the chain of requests will consist of a single request in most cases.
Alpha Vantage can process only one ticket at a time, so that a chain of N consecutive requests needs to be raised at each takt iteration in order to process a set of N tickers.
Those N requests will be timely spaced by the interval defined here.
But even in the Yahoo case, it may happen that one fetch request takes so long time to complete that the subsequent request gets cancelled due to the restriction that no two requests may coexist.
In that case the cancelled request is reissued after the lapse of the time interval defined here.