Hi, did some quick research and found below, hope this would help you!
The number of data page instances for a container reaches the set limit
By default, the Pega 7 Platform can maintain 1000 read-only unique instances of a data page per thread. You can change this value by editing the dynamic system setting datapages/mrucapacity.
There are different data page instance containers for the thread, requestor, and node level. Each user can have both requestor-level and thread-level data pages up to the limit established. Additionally, each node can have any number of requestors, and each requestor can have many threads. See Contrasting PRThread objects and Java threads.
For each container:
If the number of instances of a data page reaches 60% of the established limit for thread-level or requestor-level containers, or 80% of the established limit for node-level containers, the system begins deleting older instances.
If the number reaches the established limit, the system deletes all data page instances that were last accessed more than 10 minutes ago for that container.
If, after that step, the number of instances of the data page still exceeds the set limit, the system tolerates an overload up to 125% of the established limit for thread-level or requestor-level containers, or 120% of the established limit for node-level containers.
If the number exceeds that overload number, the system deletes instances (regardless of when they were last accessed) until the number of entries in the cache is below the set limit.