ASF GitHub Bot commented on CLOUDSTACK-10320:

DaanHoogland commented on issue #2481: CLOUDSTACK-10320 - Invalid pair for 
response object breaking response parsing
URL: https://github.com/apache/cloudstack/pull/2481#issuecomment-372735409
   nice find, dirty hack, though maybe justified. Isn't the proper solution to 
put both queries in a transaction, @marcaurele ? 

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> Invalid pair for response object breaking response parsing
> ----------------------------------------------------------
>                 Key: CLOUDSTACK-10320
>                 URL: https://issues.apache.org/jira/browse/CLOUDSTACK-10320
>             Project: CloudStack
>          Issue Type: Bug
>      Security Level: Public(Anyone can view this level - this is the 
> default.) 
>          Components: API
>            Reporter: Marc-Aurèle Brothier
>            Assignee: Marc-Aurèle Brothier
>            Priority: Major
> Under some circumstances, the API is returning an invalid response, for 
> simplicity I will expose the JSON case. The API response on a 
> listVirtualMachines can be this string:
> {code:java}
> { "listvirtualmachinesresponse" :  ] } }{code}
> To understand how this is possible, assume you have more than one management 
> server and one is processing the destroy of a virtual machine in the account 
> X which is the only one it has. Another process is returning the result of 
> listVirtualMachines for that same account X. During the listVM command, the 
> result set is fetch with a searchAndDistinctCount due to the view 
> ([https://github.com/apache/cloudstack/blob/master/server/src/main/java/com/cloud/api/query/QueryManagerImpl.java#L1024).]
>  This is done through 2 queries in the GenericDao 
> [https://github.com/apache/cloudstack/blob/master/framework/db/src/main/java/com/cloud/utils/db/GenericDaoBase.java#L1323]
>  and if you encounter the _right_ conditions, the VM will be marked as 
> removed in between those 2 queries. This results in having a Pair result with 
> at least one object but a count of 0. Then following how is done the 
> serialization of the response at 
> [https://github.com/apache/cloudstack/blob/master/server/src/main/java/com/cloud/api/response/ApiResponseSerializer.java#L86]
>  you will reach the case where your output is the one previously mentioned.
> To overcome this issue, there isn't a true fix but only a better pair 
> response to ensure a correct response formatting. If the result set contains 
> at least something, the count cannot be 0 but we cannot guess the correct 
> answer, but only state it has at least one element.

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