GEPS 038: Enhanced Transaction Log
The purpose of this GEPS is to explore the implementation and functionality of an enhanced transaction log.
Currently, Gramps has a Undo/Redo system that operates as follows:
- All database operations (except imports) are stored in a undo/redo system.
- The system is managed by two data structures:
- an in-memory transactions that keep track of a message, a list of record IDs, and a timestamp
- an associated database with pickled old/new data
- the database is deleted on family tree closing
- the undo/redo system is cleared when an import is performed
UI of current stack:
The system can be easily adapted so that:
- the database is deleted
- the stored data can be loaded back into the undo/redo system
However, the current database only stores the lowest undo info, and doesn't store:
1. the transaction comment message 2. what set of undo records go together as a batch 3. the time stamp
A patch is attached for BSDDB-based databases that allows a persistent undo/redo, except that:
1. a transaction comment is generated "Undo #N" 2. all batch commits are now single entries 3. time stamp is given the current time
Here is the patch for master:
The system could easily be adapted for complete persistent undo functionality if the comment, batch set, and time stamp were also stored in the database.
1. Undo/Redo is a "stack"; things undone are lost if new things are done 2. All is lost if anything is imported into this tree 3. Undo's must be done sequentially; you can't cherry-pick one change---you have to do them all (this ensures consistency, but is often not necessary for BSDDB (say, if you are just changing a field, such as name)). Other backends may need this consistency, even in a field change.
4. Undo/Redo is a BSDDB database; if you can't open other databases (say, due to internal file change), then you might not be able to open this. Each pickled old/new row could be a single text file. 5. With patch, database keeps growing. UI could get overwhelmed with a long-edited file 6. UI doesn't show any details (eg diff of old/new) of proposed undo/redo 7. No user entered message (like a git commit message)
1. 'a routine which restores a .gramps file and applies log file. This would bring a tree up to "current".' (RonJohn) 2. store in human-readable, non-binary format (RonJohn) 3. storage could be XML or JSON