Modifying the reap interval can improve performance, but setting it without considering the nature of your sessions and business logic can cause data inconsistency, especially for time-based persistence-frequency.
For example, if you set the reap interval to 60 seconds, the value of session data will be recorded every 60 seconds. But if a client accesses a servlet to update a value at 20 second increments, then inconsistencies will result.
For example, consider an online auction scenario as follows:
Bidding starts at $5, in 60 seconds the value recorded will be $8 (three 20 second intervals).
During the next 40 seconds, the client starts incrementing the price. The value the client sees is $10.
During the client’s 20 second rest, the Application Server stops and starts in 10 seconds. As a result, the latest value recorded at the 60 second interval ($8) is be loaded into the session.
The client clicks again expecting to see $11; but instead sees is $9, which is incorrect.
So, to avoid data inconsistencies, take into the account the expected behavior of the application when adjusting the reap interval.