sqlite_backup

This exposes the python stdlib sqlite.backup function as a library, with a couple extra steps.

The main purpose for writing this is to copy sqlite databases that you may not own -- perhaps it belongs to an application (e.g., your browser) and is locked since that's currently open, or the OS keeps it open while the computer is active (e.g. Mac with iMessage)

Features

• Has the option (true by default) to first safely copy the database from disk to a temporary directory, which is:
  • useful in case the source is in read-only mode (e.g. in some sort of docker container)
  • safer if you're especially worried about corrupting or losing data
• Uses Cpythons Connection.backup, which directly uses the underlying Sqlite C code
• Performs a wal_checkpoint and sets journal_mode=DELETE after copying to the destination, to remove the WAL (write-ahead log; temporary database file). Typically the WAL is removed when the database is closed, but particular builds of sqlite, the default sqlite installed on mac, or sqlite compiled with SQLITE_DBCONFIG_NO_CKPT_ON_CLOSE enabled or SQLITE_FCNTL_PERSIST_WAL may prevent that -- so the checkpoint exists to ensure there are no temporary files leftover

In short, this prioritizes safety of the data over performance (temporarily copying data files to /tmp) - because we often don't know what the application may be doing while we're copying underlying sqlite databases

The initial backup function and some tests were extracted out of the karlicoss/HPI core/sqlite module

If other tools exist to do this, please let me know!

Installation

Requires python3.8+

To install with pip, run:

pip install sqlite_backup

Usage

Usage: sqlite_backup [OPTIONS] SOURCE_DATABASE DESTINATION

  SOURCE_DATABASE is the database to copy

  DESTINATION is where to write the database. If a directory, uses
  the SOURCE_DATABASE name. If a file, the directory must exist,
  and the destination file must not already exist (to prevent
  possibly overwriting old data)

Options:
  --debug                         Increase log verbosity  [default: False]
  --wal-checkpoint / --no-wal-checkpoint
                                  After writing to the destination, run a
                                  checkpoint to truncate the WAL to zero bytes
                                  [default: wal-checkpoint]
  --copy-use-tempdir / --no-copy-use-tempdir
                                  Copy the source database files to a
                                  temporary directory, then connect to the
                                  copied files  [default: copy-use-tempdir]
  --copy-retry INTEGER            If the files change while copying to the
                                  temporary directory, retry <n> times
                                  [default: 100]
  --copy-retry-strict / --no-copy-retry-strict
                                  Throws an error if this fails to safely copy
                                  the database files --copy-retry times
                                  [default: copy-retry-strict]
  --help                          Show this message and exit.  [default:
                                  False]

For usage in python, use the sqlite_backup function, see the docs

If you plan on reading from these backed up databases (and you're not planning on modifying these at all), I would recommend using the mode=ro (readonly) or immutable flags when connecting to the database. In python, like:

import sqlite3
from typing import Iterator

def sqlite_connect(database: str) -> Iterator[sqlite3.Connection]:
    try:
        # or for immutable, f"file:{database}?immutable=1"
        with sqlite3.connect(f"file:{database}?mode=ro", uri=True) as conn:
            yield conn
    finally:
        conn.close()

with sqlite_connect("/path/to/database") as conn:
    conn.execute("...")

Example

sqlite_backup --debug ~/.mozilla/firefox/ew9cqpqe.dev-edition-default/places.sqlite ./firefox.sqlite
[D 220202 13:00:32 core:110] Source database files: '['/home/username/.mozilla/firefox/ew9cqpqe.dev-edition-default/places.sqlite', '/home/username/.mozilla/firefox/ew9cqpqe.dev-edition-default/places.sqlite-wal']'
[D 220202 13:00:32 core:111] Temporary Destination database files: '['/tmp/tmpm2nhl1p3/places.sqlite', '/tmp/tmpm2nhl1p3/places.sqlite-wal']'
[D 220202 13:00:32 core:64] Copied from '/home/username/.mozilla/firefox/ew9cqpqe.dev-edition-default/places.sqlite' to '/tmp/tmpm2nhl1p3/places.sqlite' successfully; copied without file changing: True
[D 220202 13:00:32 core:64] Copied from '/home/username/.mozilla/firefox/ew9cqpqe.dev-edition-default/places.sqlite-wal' to '/tmp/tmpm2nhl1p3/places.sqlite-wal' successfully; copied without file changing: True
[D 220202 13:00:32 core:240] Running backup, from '/tmp/tmpm2nhl1p3/places.sqlite' to '/home/username/Repos/sqlite_backup/firefox.sqlite'
Backed up /home/username/.mozilla/firefox/ew9cqpqe.dev-edition-default/places.sqlite to /home/username/Repos/sqlite_backup/firefox.sqlite

Tests

git clone 'https://github.com/purarue/sqlite_backup'
cd ./sqlite_backup
pip install '.[testing]'
mypy ./sqlite_backup
pytest