Check_MK Werk 6688: Improved performance for HS/SW history archive

ID: 6688 Title: Improved performance for HS/SW history archive Component: HW/SW Inventory Level: 1 Class: New feature Version: 1.6.0i1 Needless file evaluations have been removed. This increases the performance when opening a subtree. Furthermore, once a delta between two trees got computed, the information is cached to disk and can be reused later on.