ever growing DeltaDataTree history (performance, leaked memory)

We observe, that eclipse is getting slower and slower while using it. After restarting it's faster.
We now have an example where the heapdump shows 39_483 org.eclipse.core.internal.dtree.DeltaDataTree/org.eclipse.core.internal.watson.ElementTree for only 956 org.eclipse.core.internal.resources.Project.
see https://github.com/eclipse-pde/eclipse.pde/issues/510#issuecomment-1472080130
i.e. a Tree with depth of 39483 / a history of such many changes in workspace.
My understanding is that the depth should be at most equal to the number of Projects build, because after Autobuild of each project the current state of the project should advance to the current workspace state and old states should be cleaned up.

The heapdump shows also that many ElementTree are hold by the builders in org.eclipse.core.internal.events.InternalBuilder.oldState

My first guess what happens is that only a subset of projects are changed. Then autobuild skips unchanged projects. Then the skipped projects keep their ancient state. Then all intermediate workspace states may stay in memory.

I currently don't have the time for further investigation :-(

org.eclipse.core.internal.dtree.DeltaDataTree、ElementTree、org.eclipse.core.internal.events.InternalBuilder.oldState 周辺の heap dump の証拠から始めます。autobuild が変更されていないプロジェクトをどのように処理し、workspace の状態を保持するかを追跡します。完了条件は、保持経路を特定し、DeltaDataTree の履歴が無制限に増加するのを防ぐ検証済みの修正を定義することです。

索引モデルが issue の本文から書いたものです。