Created attachment 156062 [details]
nps snapshot

This happened when I tried to undo another slow operation (filed at #255185). The original source file has 548 lines, but the replace operation was done on a small part (20 lines more or less). I will investigate further to reproduce it in a source that I can disclosure.

This is the undo operation for the issue #255185 in "big" Java files (578 lines).

Ok, now I can reproduce it with the following class.

package nb;

import java.util.Collection;
import java.util.Optional;
import java.util.function.BiFunction;
import java.util.function.BiPredicate;

public class SampleClass {

  public <T> void someMethod(final Collection<T> dtos,
          final BiPredicate<T, Collection<XXX>> is,
          final BiFunction<T, XXX.Builder, XXX> from,
          final BiFunction<T, Collection<XXX>, Optional<XXX>> findXXX) {
    someCollection.forEach(someObject::removeXXX);
  }

}

Steps to reproduce:
1. Select the whole method 'someMethod', press Ctrl + H
2. Put XXX for 'Find What', and MoreXXX for 'Replace With'
3. The result is as below
4. Now undo the operation, and you can see the report for this issue.

public <T> void someMethod(final Collection<T> dtos,
          final BiPredicate<T, Collection<MoreXXX>> is,
          final BiFunction<T, MoreXXX.Builder, MoreXXX> from,
          final BiFunction<T, Collection<MoreXXX>, Optional<MoreXXX>> findMoreXXX) {
    someCollection.forEach(someObject::removeMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreMoreXXX);
  }

This low perfomance is caused by search and replace bug. Undo was replacing many replaces (it is many small changes (more than 290).