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.
Please note that schemachange is a community-developed tool, not an official Snowflake offering. It comes with no support or warranty.
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:
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:
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 accidently (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:
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.
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.
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:
secret in it.
config-version: 1
vars:
bucket_name: S3://...... # not a secret
secret_key: 567576D8E # a secret
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 autoescaping 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 by using the -c (or --change-history-table) parameter. 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 will fail if the table does not exist.
Additionally, if the --create-change-history-table parameter is given, then schemachange will attempt to create the schema and table associated with the change history table. schemachange will not attempt to create the database for the change history table, so that must be created ahead of time, even when using the --create-change-history-table parameter.
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 snowflake's default authenticator, External Oauth, Browswer based SSO and Programmatic SSO options supported by the Snowflake Python Connector. Set the environment variable SNOWFLAKE_AUTHENTICATOR to one of the following
| Authentication Option | Expected Value |
|---|---|
| Default Password Authenticator | snowflake |
| Key Pair Authenticator | snowflake |
| External Oauth | oauth |
| Browser based SSO | externalbrowser |
| Programmatic SSO (Okta Only) | Okta URL endpoint for your Okta account typically in the form https://<okta_account_name>.okta.com OR https://<okta_account_name>.oktapreview.com |
If an authenticator is unsupported, then schemachange will default to snowflake. If the authenticator is snowflake, and both password and key pair values are provided then schemachange will use the password over the key pair values.
The Snowflake user password for SNOWFLAKE_USER is required to be set in the environment variable SNOWFLAKE_PASSWORD prior to calling the script. schemachange will fail if the SNOWFLAKE_PASSWORD environment variable is not set. The environment variable SNOWFLAKE_AUTHENTICATOR will be set to snowflake if it not explicitly set.
DEPRECATION NOTICE: The SNOWSQL_PWD environment variable is deprecated but currently still supported. Support for it will be removed in a later version of schemachange. Please use SNOWFLAKE_PASSWORD instead.
The Snowflake user encrypted private key for SNOWFLAKE_USER is required to be in a file with the file path set in the environment variable SNOWFLAKE_PRIVATE_KEY_PATH. Additionally, the password for the encrypted private key file is required to be set in the environment variable SNOWFLAKE_PRIVATE_KEY_PASSPHRASE. If the variable is not set, schemachange will assume the private key is not encrypted. These two environment variables must be set prior to calling the script. Schemachange will fail if the SNOWFLAKE_PRIVATE_KEY_PATH is not set.
An Oauth Configuration can be made in the YAML Config File or passing an equivalent json dictionary to the switch --oauth-config. Invoke this method by setting the environment variable SNOWFLAKE_AUTHENTICATOR to the value oauth prior to calling schemachange. Since different Oauth providers may require different information the Oauth configuration uses four named variables that are fed into a POST request to obtain a token. Azure is shown in the example YAML but other providers should use a similar pattern and request payload contents.
data element of the request.headers element of the request.It is recomended to use the YAML file and pass oauth secrets into the configuration using the templating engine instead of the command line option.
External browser authentication can be used for local development by setting the environment variable SNOWFLAKE_AUTHENTICATOR to the value externalbrowser prior to calling schemachange.
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.
For clients that do not have a browser, can use the popular SaaS Idp option to connect via Okta. This will require the Okta URL that you utilize for SSO.
Okta authentication can be used setting the environment variable SNOWFLAKE_AUTHENTICATOR to the value of your okta endpoint as a fully formed URL ( E.g. https://<org_name>.okta.com) prior to calling schemachange.
** NOTE**: Please disable Okta MFA for the user who uses Native SSO authentication with client drivers. Please consult your Okta administrator for more information.
Parameters to schemachange can be supplied in two different ways:
If supplied by both the command line and the YAML file, The command line overides the YAML values.
Additionally, regardless of the approach taken, the following paramaters are required to run schemachange:
Plese see Usage Notes for the account Parameter (for the connect Method) for more details on how to structure the account name.
schemachange expects the YAML config file to be named schemachange-config.yml and looks for it by default in the current folder. The folder can be overridden by using the --config-folder command line argument (see Command Line Arguments below for more details).
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
# The name of the snowflake account (e.g. xy12345.east-us-2.azure).
# You can also use the regionless format (e.g. myorgname-accountname)
# for privatelink accounts, suffix the account value with privatelink (e.g. <account>.privatelink)
snowflake-account: 'xy12345.east-us-2.azure'
# The name of the snowflake user
snowflake-user: 'user'
# The name of the default role to use. Can be overrideen in the change scripts.
snowflake-role: 'role'
# The name of the default warehouse to use. Can be overridden in the change scripts.
snowflake-warehouse: 'warehouse'
# The name of the default database to use. Can be overridden in the change scripts.
snowflake-database: null
# The name of the default schema to use. Can be overridden in the change scripts.
snowflake-schema: 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:
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'
# Information for Oauth token requests
oauthconfig:
# url Where token request are posted to
token-provider-url: 'https://login.microsoftonline.com/{{ env_var('AZURE_ORG_GUID', 'default') }}/oauth2/v2.0/token'
# name of Json entity returned by request
token-response-name: 'access_token'
# Headers needed for successful post or other security markings ( multiple labeled items permitted
token-request-headers:
Content-Type: "application/x-www-form-urlencoded"
User-Agent: "python/schemachange"
# Request Payload for Token (it is recommended pass
token-request-payload:
client_id: '{{ env_var('CLIENT_ID', 'default') }}'
username: '{{ env_var('USER_ID', 'default') }}'
password: '{{ env_var('USER_PASSWORD', 'default') }}'
grant_type: 'password'
scope: '{{ env_var('SESSION_SCOPE', 'default') }}'
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] [-f ROOT_FOLDER] [-m MODULES_FOLDER] [-a SNOWFLAKE_ACCOUNT] [-u SNOWFLAKE_USER] [-r SNOWFLAKE_ROLE] [-w SNOWFLAKE_WAREHOUSE] [-d SNOWFLAKE_DATABASE] [-s SNOWFLAKE_SCHEMA] [-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.yml file (the default is the current working directory) |
| -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 |
| -a SNOWFLAKE_ACCOUNT, --snowflake-account SNOWFLAKE_ACCOUNT | The name of the snowflake account (e.g. xy12345.east-us-2.azure). |
| -u SNOWFLAKE_USER, --snowflake-user SNOWFLAKE_USER | The name of the snowflake user |
| -r SNOWFLAKE_ROLE, --snowflake-role SNOWFLAKE_ROLE | The name of the role to use |
| -w SNOWFLAKE_WAREHOUSE, --snowflake-warehouse SNOWFLAKE_WAREHOUSE | The name of the default warehouse to use. Can be overridden in the change scripts. |
| -d SNOWFLAKE_DATABASE, --snowflake-database SNOWFLAKE_DATABASE | The name of the default database to use. Can be overridden in the change scripts. |
| -s SNOWFLAKE_SCHEMA, --snowflake-schema SNOWFLAKE_SCHEMA | The name of the default schema to use. Can be overridden in the change scripts. |
| -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 (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. |
| --oauth-config | Define values for the variables to Make Oauth Token requests (e.g. {"token-provider-url": "https//...", "token-request-payload": {"client_id": "GUID_xyz",...},... })' |
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:
--create-change-history-table parameter (just make sure the Snowflake user you're running schemachange with has privileges to create a schema and table in that database)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] [-a SNOWFLAKE_ACCOUNT] [-u SNOWFLAKE_USER] [-r SNOWFLAKE_ROLE] [-w SNOWFLAKE_WAREHOUSE] [-d SNOWFLAKE_DATABASE] [-s SNOWFLAKE_SCHEMA] [-c CHANGE_HISTORY_TABLE] [--vars VARS] [--create-change-history-table] [-ac] [-v] [--dry-run] [--query-tag QUERY_TAG] [--oauth-config OUATH_CONFIG]
Or if installed via pip, it can be executed as follows:
schemachange [-h] [--config-folder CONFIG_FOLDER] [-f ROOT_FOLDER] [-a SNOWFLAKE_ACCOUNT] [-u SNOWFLAKE_USER] [-r SNOWFLAKE_ROLE] [-w SNOWFLAKE_WAREHOUSE] [-d SNOWFLAKE_DATABASE] [-s SNOWFLAKE_SCHEMA] [-c CHANGE_HISTORY_TABLE] [--vars VARS] [--create-change-history-table] [-ac] [-v] [--dry-run] [--query-tag QUERY_TAG] [--oauth-config OUATH_CONFIG]
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
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:
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 ran like so:
pip install schemachange --upgrade
schemachange [-h] [-f ROOT_FOLDER] -a SNOWFLAKE_ACCOUNT -u SNOWFLAKE_USER -r SNOWFLAKE_ROLE -w SNOWFLAKE_WAREHOUSE [-d SNOWFLAKE_DATABASE] [-s SNOWFLAKE_SCHEMA] [-c CHANGE_HISTORY_TABLE] [--vars VARS] [--create-change-history-table] [-ac] [-v] [--dry-run] [--query-tag QUERY_TAG] [--oauth-config OUATH_CONFIG]
Or if you prefer docker, set the environment variables and run like so:
docker run -it --rm \
--name schemachange-script \
-v "$PWD":/usr/src/schemachange \
-w /usr/src/schemachange \
-e ROOT_FOLDER \
-e SNOWFLAKE_ACCOUNT \
-e SNOWFLAKE_USER \
-e SNOWFLAKE_ROLE \
-e SNOWFLAKE_WAREHOUSE \
-e SNOWFLAKE_PASSWORD \
python:3 /bin/bash -c "pip install schemachange --upgrade && schemachange -f $ROOT_FOLDER -a $SNOWFLAKE_ACCOUNT -u $SNOWFLAKE_USER -r $SNOWFLAKE_ROLE -w $SNOWFLAKE_WAREHOUSE"
Either way, don't forget to set the SNOWFLAKE_PASSWORD environment variable if using password authentication!
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.
FAQs
A Database Change Management tool for Snowflake
We found that schemachange demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 2 open source maintainers collaborating on the project.
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