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I'll try and answer these 
.
1) frequent requests
I'm wondering if making too many frequent requests to an endpoint will affect the ES, or if the effects would be isolated to the SmartConnector / endpoint?
In general making too many requests to anything will affect it. I guess it depends on what you mean by by frequent . Since the SoapEwsRestProvider uses EWS behind the scenes, it would affect the ES if you are really really pounding on it.
2) polling vs proxy
Does the endpoint poll the ES, or is it just acting as a proxy (translating REST requests to Soap) between the client and the ES?
In general this is what it does, but it does have some caching involved for some methods (Trends/ AlarmEvents/ Subscriptions/ Notifications).
3) caching (if proxied)
if the SmartConnector is acting as a proxy, does it try to mitigate traffic to the ES by caching frequently requested values?
Some things are cached for sure, alarm events, trend records, last known values for subscriptions and notifications, but things like folder Children are not cached, as these can change often.
4) It seems unlikely, but perhaps the Smart Connector creates COV subscriptions to frequently requested (or all) values in the ES?
There is nothing today that is creating COV subscriptions (as this concept doesn't exist in EWS, everything must be polled). However, using the /Subscriptions and /Notifications will use EWS Subscriptions behind the scenes, which is as good as you can get from a performance and overhead perspective.
5) requesting values from Bacnet / IO values
For Bacnet and other IO devices, does requesting the value end up creating more traffic on IO bus, or are values directly pulled from the ES? If yes, does creating a shortcut get around this potential pitfall?
When polling values from SBO, the REST provider uses EWS Subscriptions behind the scenes. EWS Subscriptions are far less taxing on the system than doing EWS GetValues or GetItems as these will send a request to the field bus every time they are called while EWS Subscriptions uses internal SBO methods to get updated values from the field bus.
6) shortcuts
Is there any any performance penalty to grouping a collection of shortcuts into a folder so as to obtain all values in a single REST request?
Not that I can see.
7) if I have a large number of points in the same folder, and I request them all simultaneously, but each in individual http GET requests, is that going to be significantly more overhead on the ES than requesting the Children of the container in a single http GET request?
Yes, if you send individual http GET requests, the REST provider will send individual EWS GetItems requests to the server.. If you do it while getting the Children of a container, it will send a single EWS GetItems request that gets them all at once, so it will be significantly less overhead for the ES to do it that way over an http GET for each. That said, if you are doing this in order to get the Values of all the children, I would suggest not doing it this way, but use the /Subscriptions and /Notifications endpoints to get the values. This will be far less overhead
Regards.
-Jeff
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I'll try and answer these .
1) frequent requests
I'm wondering if making too many frequent requests to an endpoint will affect the ES, or if the effects would be isolated to the SmartConnector / endpoint?
In general making too many requests to anything will affect it. I guess it depends on what you mean by by frequent . Since the SoapEwsRestProvider uses EWS behind the scenes, it would affect the ES if you are really really pounding on it.
2) polling vs proxy
Does the endpoint poll the ES, or is it just acting as a proxy (translating REST requests to Soap) between the client and the ES?
In general this is what it does, but it does have some caching involved for some methods (Trends/ AlarmEvents/ Subscriptions/ Notifications).
3) caching (if proxied)
if the SmartConnector is acting as a proxy, does it try to mitigate traffic to the ES by caching frequently requested values?
Some things are cached for sure, alarm events, trend records, last known values for subscriptions and notifications, but things like folder Children are not cached, as these can change often.
4) It seems unlikely, but perhaps the Smart Connector creates COV subscriptions to frequently requested (or all) values in the ES?
There is nothing today that is creating COV subscriptions (as this concept doesn't exist in EWS, everything must be polled). However, using the /Subscriptions and /Notifications will use EWS Subscriptions behind the scenes, which is as good as you can get from a performance and overhead perspective.
5) requesting values from Bacnet / IO values
For Bacnet and other IO devices, does requesting the value end up creating more traffic on IO bus, or are values directly pulled from the ES? If yes, does creating a shortcut get around this potential pitfall?
When polling values from SBO, the REST provider uses EWS Subscriptions behind the scenes. EWS Subscriptions are far less taxing on the system than doing EWS GetValues or GetItems as these will send a request to the field bus every time they are called while EWS Subscriptions uses internal SBO methods to get updated values from the field bus.
6) shortcuts
Is there any any performance penalty to grouping a collection of shortcuts into a folder so as to obtain all values in a single REST request?
Not that I can see.
7) if I have a large number of points in the same folder, and I request them all simultaneously, but each in individual http GET requests, is that going to be significantly more overhead on the ES than requesting the Children of the container in a single http GET request?
Yes, if you send individual http GET requests, the REST provider will send individual EWS GetItems requests to the server.. If you do it while getting the Children of a container, it will send a single EWS GetItems request that gets them all at once, so it will be significantly less overhead for the ES to do it that way over an http GET for each. That said, if you are doing this in order to get the Values of all the children, I would suggest not doing it this way, but use the /Subscriptions and /Notifications endpoints to get the values. This will be far less overhead
Regards.
-Jeff
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I think I need a little more clarification about a couple of things:
π When I send a GET /Values/{id} or GET /Containers/{id}/Children request, does this result in a corresponding EWS getValues and EWS getItems, or is this handled by EWS Subscriptions?
GET /Values/{id} is backed by a GetItems request to the ValueItem requested. GET /Containers/{id}/Children is backed by a combination of GetContainerItems and GetItems as needed for any additional properties that are returned as part of the Item type models. If you do a GET /Values/{id}/Value this is backed by GetValues (note that this REST endpoint only allows for a single {id} at a time)
9) Is there a document that describes how to use the /Subscriptions and /Notifications of the REST endpoint?
This question has been answered on this forum before 
, please take a look at: https://community.se.com/message/108252?commentID=108252#comment-108252
Regards,
-Jeff
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I definitely wouldn't do that!
/Subscriptions/Create does a EWS 'Subscribe' request.
/Notifications/Create will actually do the EWS 'GetNotification' request and cache that data then the /Notifications/{id}/Items will simply retrieve these values from the cache for you.
Therefore if you are doing /Notifications/Create followed by /Notifications/{id}/Items at some absurd high frequency, it's possible that could have a negative affect on the ES. Personally, I wouldn't do this any faster than 1 second apart just to be safe.. But because the EWS subscription mechanism in general way better as far as affecting the ES, then in theory you could do much faster.. It would just involve some testing on your end to make sure you aren't killing the ES .
Another thing of note, which I just ran into today, based on another post in this forum is that the 'ChangesOnly' functionality in /Notifications/Create doesn't seem to be supported by SBO. (Honestly, its probably an SBO bug that they are unlikely to fix anytime soon..) In order to get this type of functionality, you would need to effectively create a new subscription every time followed by it's first Notification..
Regards,
-Jeff
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As long as you are using ChangesOnly = True, then you should be all set with what you layed out .
Regards,
-Jeff
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