Consider elements in the undo/redo stack during garbage collection #664
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Nov 15, 2023
1. Define reverse operations of Object.Set Object.Remove:
1.1 Modified the set operation to compare `executedAt` with
`getPositionedAt()` during value setting, addressing issues
during undo.
1.2 Set `movedAt` when the value is reassigned during undo.
2. Handle edge cases:
When the target element is deleted by other peers
Implemented handling to skip execution of reverse operations
during undo and redo if the element has been deleted.
3. Add whiteboard example:
3.1. Feature Introduction - Added a whiteboard example for testing
undo redo operations.
3.2. Variables Added for Displaying Yorkie Data - Added
`CRDTRoot.opsForTest` and `CRDTElement.toJSForTest`.
3.3. Additional Features to Apply (Todo) - Planned features include
implementing history pause/resume, subscribing to history
changes, and applying reverse operations for `array.add` and `array.remove`.
4. TODOs
4.1. Set nested objects (yorkie-team/yorkie#663)
- Modified set operation to handle nested objects.
4.2. When the target element is garbage-collected (yorkie-team/yorkie#664)
- Considering elements referenced by operations in the
undo/redo stack during garbage collection.
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Co-authored-by: Youngteac Hong <susukang98@gmail.com>
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Description:
The current garbage collection behavior involves deleting elements that document replicas can no longer reference. If an element has been deleted and it occurred before minSyncedTicket, it is considered not referable by each replica. However, with the introduction of Undo/Redo, even deleted elements can still be referenced through the undo/redo stack. Consequently, they should not be garbage collected. If garbage collection occurs on elements that are still referenced in the undo/redo stack, it may lead to issues where these elements cannot be found. (Refer to the test code: Should handle the case of reverse operations referencing already garbage-collected elements) Therefore, during garbage collection, it is necessary to check elements referenced by operations in the undo/redo stack.
Ensure that elements referenced by operations in the undo/redo stack are not prematurely deleted during garbage collection.
Why:
The reason for this change is that even though elements may have been deleted, they can be referenced again through the undo/redo stack. As a result, an additional condition needs to be added to the garbage collection process to account for elements referenced in the undo/redo stack.
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