gem-hunter

Database Snapshot, List, and Restore

Take lightning fast snapshots of your local Postgres databases.

DSLR is a tool that allows you to quickly take and restore database snapshots when you're writing database migrations, switching branches, or messing with SQL.

It's meant to be a spiritual successor to Stellar.

Important: DSLR is intended for development use only. It is not advisable to use DSLR on production databases.

DSLR is much faster than the standard pg_dump/pg_restore approach to snapshots.

DSLR is 8x faster at taking snapshots and 3x faster at restoring snapshots compared to the pg_dump/pg_restore approach.

I spun up Postgres 12.3 using Docker, created a test database, and filled it with 1GB of random data using this script:

CREATE TABLE large_test (num1 bigint, num2 double precision, num3 double precision);

INSERT INTO large*test (num1, num2, num3)
SELECT round(random() * 10), random(), random() \_ 142
FROM generate_series(1, 20000000) s(i);

I used the following commands to measure the execution time:

time dslr snapshot my-snapshot
time dslr restore my-snapshot
time pg_dump -Fc -f export.dump
time pg_restore --no-acl --no-owner export.dump

I ran each command three times and plotted the mean in the chart.

Here's the raw data:

pip install DSLR psycopg2 # or psycopg2-binary, or psycopg

Install using pipx

pipx install DSLR[psycopg2] # or psycopg2-binary, or psycopg

Install using uv

uv tool install 'DSLR[psycopg2]' # or psycopg2-binary, or psycopg

Note: The DSLR export and import snapshot commands require pg_dump and pg_restore to be present in your PATH, so you will need the Postgres CLI utilities if you want to use those commands.

Bash

Add this to ~/.bashrc:

eval "$(_DSLR_COMPLETE=bash_source dslr)"

Zsh

Add this to ~/.zshrc:

eval "$(_DSLR_COMPLETE=zsh_source dslr)"

Fish

Add this to ~/.config/fish/completions/dslr.fish:

eval (env _DSLR_COMPLETE=fish_source dslr)

This is the same file used for the activation script method below. For Fish it’s probably always easier to use that method.

Using eval means that the command is invoked and evaluated every time a shell is started, which can delay shell responsiveness. To speed it up, write the generated script to a file, then source that.

Bash

Save the script somewhere.

_DSLR_COMPLETE=bash_source dslr > ~/.dslr-complete.bash

Source the file in ~/.bashrc.

. ~/.dslr-complete.bash

Zsh

Save the script somewhere.

_DSLR_COMPLETE=zsh_source dslr > ~/.dslr-complete.zsh

Source the file in ~/.zshrc.

. ~/.dslr-complete.zsh

Fish

Save the script to ~/.config/fish/completions/foo-bar.fish:

_DSLR_COMPLETE=fish_source dslr > ~/.config/fish/completions/dslr.fish

You can tell DSLR which database to take snapshots of in a few ways:

DATABASE_URL

If the DATABASE_URL environment variable is set, DSLR will use this to connect to your target database.

export DATABASE_URL=postgres://username:password@host:port/database_name

dslr.toml

If a dslr.toml file exists in the current directory, DSLR will read its settings from there. DSLR will prefer this over the environment variable.

url = 'postgres://username:password@host:port/database_name'

--url option

Finally, you can explicitly pass the connection string via the --url option. This will override any of the above settings.

$ dslr snapshot my-first-snapshot
Created new snapshot my-first-snapshot

$ dslr restore my-first-snapshot
Restored database from snapshot my-first-snapshot

$ dslr list

  Name                Created            Size
 ─────────────────────────────────────────────
  my-first-snapshot   2 minutes ago   3253 kB

$ dslr rename my-first-snapshot fresh-db
Renamed snapshot my-first-snapshot to fresh-db

$ dslr delete some-old-snapshot
Deleted some-old-snapshot

$ dslr export my-feature-test
Exported snapshot my-feature-test to my-feature-test_20220730-075650.dump

$ dslr import snapshot-from-a-friend_20220730-080632.dump friend-snapshot
Imported snapshot friend-snapshot from snapshot-from-a-friend_20220730-080632.dump

To force overwriting an existing snapshot in non-interactive shell use the flag -y:

$ dslr snapshot my-first-snapshot -y
Updated snapshot my-first-snapshot

DSLR takes snapshots by cloning databases using Postgres' Template Databases functionality. This is the main source of DSLR's speed.

This means that taking a snapshot is just creating a new database using the main database as the template. Restoring a snapshot is just deleting the main database and creating a new database using the snapshot database as the template. So on and so forth.

MIT