Add description about placeholders of database.properties (#1498)

Co-authored-by: Josh Wong <joshua.wong@scalar-labs.com> Co-authored-by: Toshihiro Suzuki <brfrn169@gmail.com>
scalar-labs · Feb 16, 2024 · 7410a4b · 7410a4b
1 parent 21dc7e5
commit 7410a4b
Showing 1 changed file with 13 additions and 0 deletions.
diff --git a/docs/configurations.md b/docs/configurations.md
@@ -180,6 +180,19 @@ The following are additional configurations available for ScalarDB:
 | `scalar.db.metadata.cache_expiration_time_secs`                  | ScalarDB has a metadata cache to reduce the number of requests to the database. This setting specifies the expiration time of the cache in seconds.                                                               | `-1` (no expiration) |
 | `scalar.db.active_transaction_management.expiration_time_millis` | ScalarDB maintains ongoing transactions, which can be resumed by using a transaction ID. This setting specifies the expiration time of this transaction management feature in milliseconds.                       | `-1` (no expiration) |
 
+## Placeholder usage
+
+You can use placeholders in the values, and they are replaced with environment variables (`${env:<ENVIRONMENT_VARIABLE_NAME>}`) or system properties (`${sys:<SYSTEM_PROPERTY_NAME>}`). You can also specify default values in placeholders like `${sys:<SYSTEM_PROPERTY_NAME>:-<DEFAULT_VALUE>}`.
+
+The following is an example of a configuration that uses placeholders:
+
+```properties
+scalar.db.username=${env:<SCALAR_DB_USERNAME>:-admin}
+scalar.db.password=${env:<SCALAR_DB_PASSWORD>}
+```
+
+In this example configuration, ScalarDB reads the username and password from environment variables. If the environment variable `SCALAR_DB_USERNAME` does not exist, ScalarDB uses the default value `admin`.
+
 ## Configuration examples
 
 This section provides some configuration examples.