out of memory error, when typing a char with 18k carets (almost the limit of "undo_max_carets": 20000)

[njwgh]

I have a file with approx 18,000 lines, max 20 chars in each line
I do Ctrl A to select all lines
Then Shift Ctrl L to put in multiple carets and hit home key to go to start of lines
Then type a character (to insert the character at all caret positions) - takes about 6 seconds
Then hit 'end' key to move caret to end of lines, then insert another character - takes about 22 seconds
When I type the third character I get "out of memory" error
I did try changing undo_max_carets option to 10000 , but that didn't help
SublimeText does each character in 3 seconds
Windows 10

[Alexey-T]

Confirmed on Linux. I Will investigate it soon. Now my notebook's SSD disk is dying and replacing Will be only next week. Im not in the town.

[Alexey-T]

I confirm the memory grow (up to 7 Gb for typing at line start with 18k carets) + slow work.
BUT for me - low value of option "undo_max_carets": 2000 HELPS. Ie memory don't grow anymore + work is much faster. 3-5 secs for typing at line start / at line end.
Even app restart is not needed if you change the option. But you must save the user.json if you edit it.

[Alexey-T]

Why the memory grows so much - because Undo-list design is not compact. for typing 1 char with 18k carets - undo-list contains 18k items and each item contains 18k*4 integers (and other infos). what will help here is redesign of Undo-list internal format. maybe I will look at it later, not sure.

Current workaround which I suggest: smaller value of "undo_max_carets". eg 1000.

EDIT
I will decrease default of "undo_max_carets" for the next version.

[njwgh]

Thanks!. I confirm that with undo_max_carets = 1000, then I can do the edits and they are quite quick.
can you explain how undo_max_carets value works. I assumed that if number of carets was > undo_max_carets then it wouldn't save any undo information, but that is obviously not how it is working.

[Alexey-T]

Maybe you tested it wrong? As I know that option must work like you guessed... So with 18k carets, option value 16k must also make it fast.

[Alexey-T]

(Marked as 'enhancement' because there is no bug but I see the room for improvement of too big memory usage)

[njwgh]

Maybe you tested it wrong? As I know that option must work like you guessed... So with 18k carets, option value 16k must also make it fast.

I think you're right. I checked again and 10000 for max_undo_carets works with my file. Not sure what happened the first time

[Alexey-T]

proper fix will be:

• don't write CaretsArray to UndoItem for multi-carets editing, except for the last affected caret. ie, we have 100 carets, and do 'arrow right' command typing a char. we must not write CaretsArray for first 99 UndoItems, only write CaretsArray for the last UndoItem. typing action is performed as grouped, so 'middle' caret info is not needed anyway
• when doing Undo for UndoItem, see if it has empty CaretsArray, and if so, don't move / delete carets at all

this will give O(caret_count) mem usage for Undo. current usage: O(caret_count^2).