When quering process instances, I want to have the option to fetch variables attached to the process instance

[ThorbenLindhauer]

This issue was imported from JIRA:

Field	Value
JIRA Link	CAM-11930
Reporter	NYBzR2x What is this name? This pseudonym name was generated based on the user name in JIRA to protect the personal data of our JIRA users. You can use this identifier to search for issues by the same reporter.
Has restricted visibility comments	false

---

User story

As a developer, I want to have the option to define variables that should be fetched with process instances, so that I do not have to run separate queries.

Background / problem

When having X open user tasks, it takes 3X REST requests to get the variables needed to evaluate and prioritize these user tasks.

i.e. Getting the variables for 100k user tasks currently requires 300k REST requests to get the variables of interest, which is taking a lot of time and strains the system severely.

Customer hint:

if the rest/tast/get-query/ also allowed to choose variable types and variables of interest all the 300K REST requests could be reduced to 1 REST request

AC

• Offer a query to fetch a process instance with defined variables attached to the process instance
• Avoid additional queries for each fetched process instance when specific variables are needed 

Links:

• is related to https://jira.camunda.com/browse/SUPPORT-7712
• is related to https://jira.camunda.com/browse/SUPPORT-7713
• is related to https://jira.camunda.com/browse/SUPPORT-7714