[lavrton]

Hey, we hit performance issues is Polotno studio (design editor). Grouping elements detaches each one and moves it into the new group. With 600 elements on a page, long time was splitCache, and it grows with every page in the document.

detach() calls IdentifierCache.splitCache, which loops over every identifier in the tree and builds each node's path to find the detached subtree. So one detach costs O(tree size), and moving N nodes costs O(N × tree size).

The fix walks only the detached subtree and reuses notifyDied to remove each node from the old cache.

detach 600 nodes (bun, production, median of 7)	before	after
tree of 600 nodes	35 ms	5.4 ms
tree of 3600 nodes	298 ms	6.0 ms

The new test in identifier.test.ts detaches 1 of 1000 items. Before the fix that read path 1001 times. It also checks that identifiers still resolve, including one nested in the detached item.

[coolsoftwaretyler]

Thanks, I'll take a look soon!

[lavrton]

@coolsoftwaretyler thanks a lot! Maybe will send couple more PR to mst or mobx. Still investigating