Looking for snowchange? You've found the right spot. snowchange has been renamed to schemachange.
schemachange is a simple python based tool to manage all of your Snowflake objects. It follows an Imperative-style approach to Database Change Management (DCM) and was inspired by the Flyway database migration tool. When combined with a version control system and a CI/CD tool, database changes can be approved and deployed through a pipeline using modern software delivery practices. As such schemachange plays a critical role in enabling Database (or Data) DevOps.
DCM tools (also known as Database Migration, Schema Change Management, or Schema Migration tools) follow one of two approaches: Declarative or Imperative. For a background on Database DevOps, including a discussion on the differences between the Declarative and Imperative approaches, please read the Embracing Agile Software Delivery and DevOps with Snowflake blog post.
For the complete list of changes made to schemachange check out the CHANGELOG.
To learn more about making a contribution to schemachange, please see our Contributing guide.
Please note that schemachange is a community-developed tool, not an official Snowflake offering. It comes with no support or warranty.
- Overview
- Project Structure
- Change Scripts
- Change History Table
- Authentication
- Configuration
- Commands
- Running schemachange
- Integrating With DevOps
- Maintainers
- Third Party Packages
- Legal
schemachange expects a directory structure like the following to exist:
(project_root)
|
|-- folder_1
|-- V1.1.1__first_change.sql
|-- V1.1.2__second_change.sql
|-- R__sp_add_sales.sql
|-- R__fn_get_timezone.sql
|-- folder_2
|-- folder_3
|-- V1.1.3__third_change.sql
|-- R__fn_sort_ascii.sql
The schemachange folder structure is very flexible. The project_root folder is specified with the -f
or --root-folder argument. schemachange only pays attention to the filenames, not the paths. Therefore, under
the project_root folder you are free to arrange the change scripts any way you see fit. You can have as many
subfolders (and nested subfolders) as you would like.
Versioned change scripts follow a similar naming convention to that used by Flyway Versioned Migrations. The script name must follow this pattern (image taken from Flyway docs):
With the following rules for each part of the filename:
- Prefix: The letter 'V' for versioned change
- Version: A unique version number with dots or underscores separating as many number parts as you like
- Separator: __ (two underscores)
- Description: An arbitrary description with words separated by underscores or spaces (can not include two underscores)
- Suffix: .sql or .sql.jinja
For example, a script name that follows this convention is: V1.1.1__first_change.sql. As with Flyway, the unique
version string is very flexible. You just need to be consistent and always use the same convention, like 3 sets of
numbers separated by periods. Here are a few valid version strings:
- 1.1
- 1_1
- 1.2.3
- 1_2_3
Every script within a database folder must have a unique version number. schemachange will check for duplicate version numbers and throw an error if it finds any. This helps to ensure that developers who are working in parallel don't accidentally (re-)use the same version number.
Repeatable change scripts follow a similar naming convention to that used by Flyway Versioned Migrations. The script name must follow this pattern (image taken from Flyway docs:
e.g:
- R__sp_add_sales.sql
- R__fn_get_timezone.sql
- R__fn_sort_ascii.sql
All repeatable change scripts are applied each time the utility is run, if there is a change in the file. Repeatable scripts could be used for maintaining code that always needs to be applied in its entirety. e.g. stores procedures, functions and view definitions etc.
Just like Flyway, within a single migration run, repeatable scripts are always applied after all pending versioned scripts have been executed. Repeatable scripts are applied in alphabetical order of their description.
Always change scripts are executed with every run of schemachange. This is an addition to the implementation of Flyway Versioned Migrations. The script name must follow this pattern:
A__Some_description.sql
e.g.
- A__add_user.sql
- A__assign_roles.sql
This type of change script is useful for an environment set up after cloning. Always scripts are applied always last.
schemachange is designed to be very lightweight and not impose too many limitations. Each change script can have any
number of SQL statements within it and must supply the necessary context, like database and schema names. The context
can be supplied by using an explicit USE <DATABASE> command or by naming all objects with a three-part
name (<database name>.<schema name>.<object name>). schemachange will simply run the contents of each script against
the target Snowflake account, in the correct order. After each script, Schemachange will execute "reset" the context (
role, warehouse, database, schema) to the values used to configure the connector.
schemachange supports the jinja engine for a variable replacement strategy. One important use of variables is to support
multiple environments (dev, test, prod) in a single Snowflake account by dynamically changing the database name during
deployment. To use a variable in a change script, use this syntax anywhere in the script: {{ variable1 }}.
To pass variables to schemachange, check out the Configuration section below. You can either use
the --vars command line parameter or the YAML config file schemachange-config.yml. For the command line version you
can pass variables like this: --vars '{"variable1": "value", "variable2": "value2"}'. This parameter accepts a flat
JSON object formatted as a string.
Nested objects and arrays don't make sense at this point and aren't supported.
schemachange will replace any variable placeholders before running your change script code and will throw an error if it finds any variable placeholders that haven't been replaced.
While many CI/CD tools already have the capability to filter secrets, it is best that any tool also does not output
secrets to the console or logs. Schemachange implements secrets filtering in a number of areas to ensure secrets are not
writen to the console or logs. The only exception is the render command which will display secrets.
A secret is just a standard variable that has been tagged as a secret. This is determined using a naming convention and either of the following will tag a variable as a secret:
- The variable name has the word
secretin it.config-version: 1 vars: bucket_name: S3://...... # not a secret secret_key: 567576D8E # a secret
- The variable is a child of a key named
secrets.config-version: 1 vars: secrets: my_key: 567576D8E # a secret aws: bucket_name: S3://...... # not a secret secrets: encryption_key: FGDSUUEHDHJK # a secret us_east_1: encryption_key: sdsdsd # a secret
schemachange uses the Jinja templating engine internally and supports: expressions, macros, includes and template inheritance.
These files can be stored in the root-folder but schemachange also provides a separate modules
folder --modules-folder. This allows common logic to be stored outside of the main changes scripts.
The demo/citibike_demo_jinja has a simple example that demonstrates this.
The Jinja auto-escaping feature is disabled in schemachange, this feature in Jinja is currently designed for where the output language is HTML/XML. So if you are using schemachange with untrusted inputs you will need to handle this within your change scripts.
Within change scripts:
schemachange records all applied changes scripts to the change history table. By default, schemachange will attempt to
log all activities to the METADATA.SCHEMACHANGE.CHANGE_HISTORY table. The name and location of the change history
table can be overriden via a command line argument (-c or --change-history-table) or the schemachange-config.yml
file ( change-history-table). The value passed to the parameter can have a one, two, or three part name (e.g. "
TABLE_NAME", or "SCHEMA_NAME.TABLE_NAME", or " DATABASE_NAME.SCHEMA_NAME.TABLE_NAME"). This can be used to support
multiple environments (dev, test, prod) or multiple subject areas within the same Snowflake account.
By default, schemachange will not try to create the change history table, and it will fail if the table does not exist.
This behavior can be altered by passing in the --create-change-history-table argument or adding
create-change-history-table: true to the schemachange-config.yml file. Even with the --create-change-history-table
parameter, schemachange will not attempt to create the database for the change history table. That must be created
before running schemachange.
The structure of the CHANGE_HISTORY table is as follows:
| Column Name | Type | Example |
|---|---|---|
| VERSION | VARCHAR | 1.1.1 |
| DESCRIPTION | VARCHAR | First change |
| SCRIPT | VARCHAR | V1.1.1__first_change.sql |
| SCRIPT_TYPE | VARCHAR | V |
| CHECKSUM | VARCHAR | 38e5ba03b1a6d2... |
| EXECUTION_TIME | NUMBER | 4 |
| STATUS | VARCHAR | Success |
| INSTALLED_BY | VARCHAR | SNOWFLAKE_USER |
| INSTALLED_ON | TIMESTAMP_LTZ | 2020-03-17 12:54:33.056 -0700 |
A new row will be added to this table every time a change script has been applied to the database. schemachange will use this table to identify which changes have been applied to the database and will not apply the same version more than once.
Here is the current schema DDL for the change history table (found in the schemachange/cli.py
script), in case you choose to create it manually and not use the --create-change-history-table parameter:
CREATE TABLE IF NOT EXISTS SCHEMACHANGE.CHANGE_HISTORY
(
VERSION VARCHAR,
DESCRIPTION VARCHAR,
SCRIPT VARCHAR,
SCRIPT_TYPE VARCHAR,
CHECKSUM VARCHAR,
EXECUTION_TIME NUMBER,
STATUS VARCHAR,
INSTALLED_BY VARCHAR,
INSTALLED_ON TIMESTAMP_LTZ
)Schemachange supports the many of the authentication methods supported by
the Snowflake Python Connector.
The authenticator can be set by setting an authenticator in the connections.toml file
The following authenticators are supported:
snowflake: Passwordoauth: External OAuthexternalbrowser: Browser-based SSOhttps://<okta_account_name>.okta.com: Okta SSOsnowflake_jwt: Private Key
If an authenticator is unsupported, an exception will be raised.
Password authentication is the default authenticator. Supplying snowflake as your authenticator will set it
explicitly. A password must be supplied in the connections.toml file
External OAuth authentication can be selected by supplying oauth as your authenticator. A token_file_path must be
supplied in the connections.toml file
Schemachange no longer supports the --oauth-config option. Prior to the 4.0 release, this library supported
supplying an --oauth-config that would be used to fetch an OAuth token via the requests library. This required
Schemachange to keep track of connection arguments that could otherwise be passed directly to the Snowflake Python
connector. Maintaining this logic in Schemachange added unnecessary complication to the repo and prevented access to
recent connector parameterization features offered by the Snowflake connector.
External browser authentication can be selected by supplying externalbrowser as your authenticator. The client will be
prompted to authenticate in a browser that pops up. Refer to
the documentation
to cache the token to minimize the number of times the browser pops up to authenticate the user.
External browser authentication can be selected by supplying your Okta endpoint as your authenticator (e.g.
https://<org_name>.okta.com). For clients that do not have a browser, can use the popular SaaS Idp option to connect
via Okta. A password must be supplied in the connections.toml file
** NOTE**: Please disable Okta MFA for the user who uses Native SSO authentication with client drivers. Please consult your Okta administrator for more information.
External browser authentication can be selected by supplying snowflake_jwt as your authenticator. The filepath to a
Snowflake user-encrypted private key must be supplied as private-key in the connections.toml
file. If the private key file is password protected, supply the password as private_key_file_pwd in
the connections.toml file. If the variable is not set, the Snowflake Python connector will
assume the private key is not encrypted.
As of version 4.0, Snowflake connection parameters must be supplied via a connections.toml file. Command-line and yaml arguments will still be supported with a deprecation warning until support is completely dropped.
Schemachange-specific parameters can be supplied in two different ways (in order of priority):
- Command Line Arguments
- YAML config file
Note: As of 4.0, vars provided via command-line argument will be merged with vars provided via YAML config.
Previously, one overwrote the other completely
Please see Usage Notes for the account Parameter (for the connect Method) for more details on how to structure the account name.
A `connections.toml filepath can be supplied in the following ways (in order of priority):
- The
--connections-file-pathcommand-line argument - The
connections-file-pathYAML value
A connection name can be supplied in the following ways (in order of priority):
- The
SNOWFLAKE_DEFAULT_CONNECTION_NAMEenvironment variable - The
--connection-namecommand-line argument - The
connection-nameYAML value
By default, Schemachange expects the YAML config file to be named schemachange-config.yml, located in the current
working directory. The YAML file name can be overridden with the
--config-file-name command-line argument. The folder can be overridden by using the
--config-folder command-line argument
Here is the list of available configurations in the schemachange-config.yml file:
config-version: 1
# The root folder for the database change scripts
root-folder: '/path/to/folder'
# The modules folder for jinja macros and templates to be used across multiple scripts.
modules-folder: null
# Override the default connections.toml file path at snowflake.connector.constants.CONNECTIONS_FILE (OS specific)
connections-file-path: null
# Override the default connections.toml connection name. Other connection-related values will override these connection values.
connection-name: null
# Used to override the default name of the change history table (the default is METADATA.SCHEMACHANGE.CHANGE_HISTORY)
change-history-table: null
# Define values for the variables to replaced in change scripts. vars supplied via the command line will be merged into YAML-supplied vars
vars:
var1: 'value1'
var2: 'value2'
secrets:
var3: 'value3' # This is considered a secret and will not be displayed in any output
# Create the change history schema and table, if they do not exist (the default is False)
create-change-history-table: false
# Enable autocommit feature for DML commands (the default is False)
autocommit: false
# Display verbose debugging details during execution (the default is False)
verbose: false
# Run schemachange in dry run mode (the default is False)
dry-run: false
# A string to include in the QUERY_TAG that is attached to every SQL statement executed
query-tag: 'QUERY_TAG'The YAML config file supports the jinja templating language and has a custom function "env_var" to access environmental variables. Jinja variables are unavailable and not yet loaded since they are supplied by the YAML file. Customisation of the YAML file can only happen through values passed via environment variables.
Provides access to environmental variables. The function can be used two different ways.
Return the value of the environmental variable if it exists, otherwise return the default value.
{{ env_var('<environmental_variable>', 'default') }}Return the value of the environmental variable if it exists, otherwise raise an error.
{{ env_var('<environmental_variable>') }}Schemachange supports a few subcommands. If the subcommand is not provided it defaults to deploy. This behaviour keeps compatibility with versions prior to 3.2.
This is the main command that runs the deployment process.
usage: schemachange deploy [-h] [--config-folder CONFIG_FOLDER] [--config-file-name CONFIG_FILE_NAME] [-f ROOT_FOLDER] [-m MODULES_FOLDER] [--connections-file-path CONNECTIONS_FILE_PATH] [--connection-name CONNECTION_NAME] [-c CHANGE_HISTORY_TABLE] [--vars VARS] [--create-change-history-table] [-ac] [-v] [--dry-run] [--query-tag QUERY_TAG]| Parameter | Description |
|---|---|
| -h, --help | Show the help message and exit |
| --config-folder CONFIG_FOLDER | The folder to look in for the schemachange config file (the default is the current working directory) |
| --config-file-name CONFIG_FILE_NAME | The file name of the schemachange config file. (the default is schemachange-config.yml) |
| -f ROOT_FOLDER, --root-folder ROOT_FOLDER | The root folder for the database change scripts. The default is the current directory. |
| -m MODULES_FOLDER, --modules-folder MODULES_FOLDER | The modules folder for jinja macros and templates to be used across mutliple scripts |
| --connections-file-path CONNECTIONS_FILE_PATH | Override the default connections.toml file path at snowflake.connector.constants.CONNECTIONS_FILE (OS specific) |
| --connection-name CONNECTION_NAME | Override the default connections.toml connection name. Other connection-related values will override these connection values. |
| -c CHANGE_HISTORY_TABLE, --change-history-table CHANGE_HISTORY_TABLE | Used to override the default name of the change history table (which is METADATA.SCHEMACHANGE.CHANGE_HISTORY) |
| --vars VARS | Define values for the variables to replaced in change scripts, given in JSON format. Vars supplied via the command line will be merged with YAML-supplied vars (e.g. '{"variable1": "value1", "variable2": "value2"}') |
| --create-change-history-table | Create the change history table if it does not exist. The default is 'False'. |
| -ac, --autocommit | Enable autocommit feature for DML commands. The default is 'False'. |
| -v, --verbose | Display verbose debugging details during execution. The default is 'False'. |
| --dry-run | Run schemachange in dry run mode. The default is 'False'. |
| --query-tag | A string to include in the QUERY_TAG that is attached to every SQL statement executed. |
This subcommand is used to render a single script to the console. It is intended to support the development and troubleshooting of script that use features from the jinja template engine.
usage: schemachange render [-h] [--config-folder CONFIG_FOLDER] [-f ROOT_FOLDER] [-m MODULES_FOLDER] [--vars VARS] [-v] script
| Parameter | Description |
|---|---|
| --config-folder CONFIG_FOLDER | The folder to look in for the schemachange-config.yml file (the default is the current working directory) |
| -f ROOT_FOLDER, --root-folder ROOT_FOLDER | The root folder for the database change scripts |
| -m MODULES_FOLDER, --modules-folder MODULES_FOLDER | The modules folder for jinja macros and templates to be used across multiple scripts |
| --vars VARS | Define values for the variables to replaced in change scripts, given in JSON format (e.g. {"variable1": "value1", "variable2": "value2"}) |
| -v, --verbose | Display verbose debugging details during execution (the default is False) |
In order to run schemachange you must have the following:
- You will need to have a recent version of python 3 installed
- You will need to have the latest Snowflake Python driver installed
- You will need to create the change history table used by schemachange in Snowflake (
see Change History Table above for more details)
- First, you will need to create a database to store your change history table (schemachange will not help you with this). For your convenience, initialize.sql file has been provided to get you started. Feel free to align the script to your organizations RBAC implementation. The setup_schemachange_schema.sql file is provided to set up the target schema that will host the change history table for each of the demo projects in this repo. Use it as a means to test the required permissions and connectivity in your local setup.
- Second, you will need to create the change history schema and table. You can do this manually (
see Change History Table above for the DDL) or have schemachange create them by running
it with the
--create-change-history-tableparameter (just make sure the Snowflake user you're running schemachange with has privileges to create a schema and table in that database)
- You will need to create (or choose) a user account that has privileges to apply the changes in your change script
- Don't forget that this user also needs the SELECT and INSERT privileges on the change history table
schemachange is a single python script located at schemachange/cli.py. It can be executed as follows:
python schemachange/cli.py [-h] [--config-folder CONFIG_FOLDER] [-f ROOT_FOLDER] [-c CHANGE_HISTORY_TABLE] [--vars VARS] [--create-change-history-table] [-ac] [-v] [--dry-run] [--query-tag QUERY_TAG] [--connections-file-path] [--connection-name]
Or if installed via pip, it can be executed as follows:
schemachange [-h] [--config-folder CONFIG_FOLDER] [-f ROOT_FOLDER] [-c CHANGE_HISTORY_TABLE] [--vars VARS] [--create-change-history-table] [-ac] [-v] [--dry-run] [--query-tag QUERY_TAG] [--connections-file-path] [--connection-name]
The demo folder in this project repository contains three schemachange demo projects for you to try out. These demos showcase the basics and a couple of advanced examples based on the standard Snowflake Citibike demo which can be found in the Snowflake Hands-on Lab. Check out each demo listed below
- Basics Demo: Used to test the basic schemachange functionality.
- Citibike Demo: Used to show a simple example of building a database and loading data using schemachange.
- Citibike Jinja Demo: Extends the citibike demo to showcase the use of macros and jinja templating.
The Citibike data for this demo comes from the NYC Citi Bike bike share program.
To get started with schemachange and these demo scripts follow these steps:
- Make sure you've completed the Prerequisites steps above
- Get a copy of this schemachange repository (either via a clone or download)
- Open a shell and change directory to your copy of the schemachange repository
- Run schemachange (see Running the Script above) with your Snowflake account details and respective demo project as the root folder (make sure you use the full path)
Here is a sample DevOps development lifecycle with schemachange:
If your build agent has a recent version of python 3 installed, the script can be run like so:
pip install schemachange --upgrade
schemachange [-h] [-f ROOT_FOLDER] [-c CHANGE_HISTORY_TABLE] [--vars VARS] [--create-change-history-table] [-ac] [-v] [--dry-run] [--query-tag QUERY_TAG] [--connections-file-path] [--connection-name]Or if you prefer docker, run like so:
docker run -it --rm \
--name schemachange-script \
-v "$PWD":/usr/src/schemachange \
-w /usr/src/schemachange \
-e ROOT_FOLDER \
-e $CONNECTION_NAME \
python:3 /bin/bash -c "pip install schemachange --upgrade && schemachange -f $ROOT_FOLDER --connections-file-path connections.toml --connection-name $CONNECTION_NAME"Either way, don't forget to configure a connections.toml file for connection parameters
- James Weakley (@jamesweakley)
- Jeremiah Hansen (@jeremiahhansen)
This is a community-developed tool, not an official Snowflake offering. It comes with no support or warranty. However, feel free to raise a GitHub issue if you find a bug or would like a new feature.
The current functionality in schemachange would not be possible without the following third party packages and all those that maintain and have contributed.
| Name | License | Author | URL |
|---|---|---|---|
| Jinja2 | BSD License | Armin Ronacher | https://palletsprojects.com/p/jinja/ |
| PyYAML | MIT License | Kirill Simonov | https://pyyaml.org/ |
| pandas | BSD License | The Pandas Development Team | https://pandas.pydata.org |
| pytest | MIT License | Holger Krekel, Bruno Oliveira, Ronny Pfannschmidt, Floris Bruynooghe, Brianna Laugher, Florian Bruhin and others | https://docs.pytest.org/en/latest/ |
| snowflake-connector-python | Apache Software License | Snowflake, Inc | https://www.snowflake.com/ |
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this tool except in compliance with the License. You may obtain a copy of the License at: http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an " AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
