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GEPS 038: Enhanced Transaction Log

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The purpose of this GEPS is to explore the implementation and functionality of an enhanced transaction log.

Overview

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:

Error creating thumbnail: Unable to save thumbnail to destination

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:

File:Persistent-undo.patch.zip

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.

Error creating thumbnail: Unable to save thumbnail to destination

Limitations

  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.

Also:

  1. 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.
  2. With patch, database keeps growing. UI could get overwhelmed with a long-edited file
  3. UI doesn't show any details (eg diff of old/new) of proposed undo/redo
  4. No user entered message (like a git commit message)

Enhancements

  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

References

  1. https://gramps-project.org/bugs/view.php?id=8853