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- GetPropertyValue Performance Problem
GetPropertyValue Performance Problem
09 Oct 2013 08:51 #1459
by support
Replied by support on topic GetPropertyValue Performance Problem
Thank you for feedback - I am very glad to hear it 
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07 Oct 2013 19:12 #1456
by jgyenese
Replied by jgyenese on topic GetPropertyValue Performance Problem
The new version is lightning fast.
Thank you.
Thank you.
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01 Oct 2013 05:10 #1447
by support
Replied by support on topic GetPropertyValue Performance Problem
Alright, thank you for update.
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30 Sep 2013 18:39 #1446
by jgyenese
Replied by jgyenese on topic GetPropertyValue Performance Problem
I will try the updated version and report back on the performance.
I do apologize for reporting the second issue when it was actually a problem in our code. We were not always checking for exceptions before accessing results(i).Value.
Thank you for your assistance.
I do apologize for reporting the second issue when it was actually a problem in our code. We were not always checking for exceptions before accessing results(i).Value.
Thank you for your assistance.
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30 Sep 2013 06:38 #1445
by support
Replied by support on topic GetPropertyValue Performance Problem
Interestingly, I have tried to reproduce the first issue now (the slow-down), and could not reproduce it either.
But I took the opportunity to implement a long-overdue change to GetPropertyValue/GetMultiplePropertyValues that improves their performance. The improvement is most significant with GetPropertyValue, but there is some improvement with GetMultiplePropertyValues as well.
The new build with this modification, labeled 5.22.397.1, is now the public build on the Web (in the download area). Please give it a try.
But I took the opportunity to implement a long-overdue change to GetPropertyValue/GetMultiplePropertyValues that improves their performance. The improvement is most significant with GetPropertyValue, but there is some improvement with GetMultiplePropertyValues as well.
The new build with this modification, labeled 5.22.397.1, is now the public build on the Web (in the download area). Please give it a try.
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28 Sep 2013 14:08 #1444
by support
Replied by support on topic GetPropertyValue Performance Problem
I have tried to reproduce the 2nd problem you mentioned, but I still think that GetMultiplePropertyValues indicates the errors correctly, i.e. as documented. It does not throw an exception if something is wrong. It returns the information about the problem in each element of the result array. You must, however, first check whether the operation was successful for each element - you cannot e.g. access the Value property if it not there.
Here is a small VBScript that I have used to verify this:
and here is its output:
Here is a small VBScript that I have used to verify this:
Rem This example shows how to get value of multiple OPC properties, and handle errors.
Option Explicit
Const Timestamp = 4
Const AccessRights = 5
Const SomeInvalidPropertyId = 999111
Dim EasyDAClient: Set EasyDAClient = CreateObject("OPCLabs.EasyDAClient.5.2")
Dim results: results = EasyDAClient.GetMultiplePropertyValues("", "OPCLabs.KitServer.2", _
Array("Simulation.Random", "SomeInvalidItem", "Trends.Ramp (1 min)", "Trends.Ramp (1 min)"), _
Array(Timestamp, AccessRights, SomeInvalidPropertyId, AccessRights))
Dim i: For i = LBound(results) To UBound(results)
If results(i).Exception Is Nothing Then
WScript.Echo "results(" & i & ").Value: " & results(i).Value
Else
WScript.Echo "results(" & i & ").Exception.Message: " & results(i).Exception.Message
End If
Nextand here is its output:
results(0).Value: 1/1/1601 2:00:00 AM
results(1).Exception.Message: The item is no longer available in the server address space.
results(2).Exception.Message: The server does not recognize the passed property ID.
results(3).Value: 3Please Log in or Create an account to join the conversation.
27 Sep 2013 02:20 #1442
by jgyenese
Replied by jgyenese on topic GetPropertyValue Performance Problem
I tried using GetMultipleProptertyValues and found a similar performance difference between calling it after a read vs before - it took 25 times longer after a read. The good news it that it is much faster than calling GetPropertyValue in a loop.
More information to share - if you try to read the property values before reading any item values, the performance does not slow down after subsequent value reads.
I did find a problem though. According to the documentation "This method [GetMultipleProptertyValues] does not throw an exception in case of OPC operation failures. Instead, the eventual exception related to each property is returned in Exception property of each returned ValueResult element." This is not correct, GetMultipleProptertyValues does indeed throw exceptions if you request a property value the server does not recognize.
More information to share - if you try to read the property values before reading any item values, the performance does not slow down after subsequent value reads.
I did find a problem though. According to the documentation "This method [GetMultipleProptertyValues] does not throw an exception in case of OPC operation failures. Instead, the eventual exception related to each property is returned in Exception property of each returned ValueResult element." This is not correct, GetMultipleProptertyValues does indeed throw exceptions if you request a property value the server does not recognize.
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26 Sep 2013 22:36 #1441
by support
Replied by support on topic GetPropertyValue Performance Problem
I will have a look at it. There will be a relation to the subscription that ReadItem internally creates, in expectation of further ReadItem-s coming in. This can be changed by a configuration. And, more importantly, GetMultiplePropertyValues should be used, instead of calling GetPropertyValue in a loop. There will be something else to it as well, but that will need further investigation.
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26 Sep 2013 21:57 #1440
by jgyenese
GetPropertyValue Performance Problem was created by jgyenese
The performance of GetPropertyValue slows down by a factor of 25 if it is preceeded by a call to ReadItemValue.
For example, open a new VB6 application project and paste the following code in the Form_Load event.
Run the code and I get an elapsed time of about 2.63 seconds.
Uncomment the "val = EasyDAClient.ReadItemValue(...)" line and I get 65 seconds.
Using version 5.22.322.1 of QuickOPC, VB6 SP6, and Windows 7 x64.
For example, open a new VB6 application project and paste the following code in the Form_Load event.
Dim results
Dim prop
Dim key
Dim val
Dim EasyDAClient
Dim tStart As Single
Dim tEnd As Single
Set EasyDAClient = CreateObject("OPCLabs.EasyDAClient.5.2")
'val = EasyDAClient.ReadItemValue("", "OPCLabs.KitServer.2", "Simulation.ReadValue_I4")
Set results = EasyDAClient.BrowseProperties("", "OPCLabs.KitServer.2", "Simulation.ReadValue_I4")
tStart = Timer
For Each key In results.Keys
Set prop = results.Item(key)
val = EasyDAClient.GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.ReadValue_I4", prop.PropertyId)
Next
tEnd = Timer
MsgBox "Elapsed time = " & CStr(tEnd - tStart) & " seconds."Run the code and I get an elapsed time of about 2.63 seconds.
Uncomment the "val = EasyDAClient.ReadItemValue(...)" line and I get 65 seconds.
Using version 5.22.322.1 of QuickOPC, VB6 SP6, and Windows 7 x64.
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