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 NOT deleted on closing
- the stored data can be loaded back into the undo/redo system
However, the current database only stores the Gramps undo info, and doesn't store:
- the transaction comment message
- what set of undo records go together as a batch
- the time stamp
A patch is attached for BSDDB-based databases that allows a persistent undo/redo, except that:
- a transaction comment is generated "Undo #N"
- all batch commits are now single entries
- 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.
- Undo/Redo is a "stack"; things undone are lost if new things are done
- All is lost if anything is imported into this tree
- 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.
- 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.
- With patch, database keeps growing. UI could get overwhelmed with a long-edited file
- UI doesn't show any details (eg diff of old/new) of proposed undo/redo
- No user entered message (like a git commit message)
- What happens if the Gramps data format changes at some point? JSON format may help to mitigate some changes.
- 'a routine which restores a .gramps file and applies log file. This would bring a tree up to "current".' (RonJohn)
- store in human-readable, non-binary format (RonJohn)
- storage could be XML or JSON
- database backend agnostic
- should work even after an import (copy of imported file could be put into directory and time-stamped)
- better UI to show diff, or at least summary of commit (eg, the following records were added: I0001, I0002, ...)
- individual changes could be cherry-picked, perhaps, with checks
- allow user comment, eg commit message
- 8853: Human-readable database transaction log