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Pre-aggregation refresh is the process of building pre-aggregations and updating them with new data. Pre-aggregation refresh is the responsibility of the refresh worker.

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Configuration

You can use the following environment variables to configure the refresh worker behavior:

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Pre-aggregation data source

By default, each data source builds and stores its pre-aggregations using its own connection. You can instead point a data source’s pre-aggregations at a dedicated connection by adding a PRE_AGGREGATIONS segment to its environment variables. When set, that source’s pre-aggregations are built on and read from the dedicated connection rather than the source’s own. Use the CUBEJS_PRE_AGGREGATIONS_DB_* variables for the default data source, and the CUBEJS_DS_<NAME>_PRE_AGGREGATIONS_DB_* variables for a named data source:
The PRE_AGGREGATIONS variant supports the same connection variables as the regular CUBEJS_DB_* / CUBEJS_DS_<NAME>_DB_* data source variables (for example _DB_HOST, _DB_PORT, _DB_USER, _DB_PASS, and _DB_SSL). Driver-specific variables take the same segment, so the dedicated connection is not limited to the _DB_* family — for example CUBEJS_PRE_AGGREGATIONS_JDBC_URL or CUBEJS_PRE_AGGREGATIONS_AWS_REGION. In the decorated form for a named data source, the DB_, JDBC_, AWS_, DATABASE, and FIREBOLT_ families are supported. Setting any one of these variables switches the data source onto the dedicated connection; there is no separate flag to enable it.
Each variable is read independently, and an unset one does not fall back to its CUBEJS_DB_* counterpart — it falls back to the driver’s own default. Configure the dedicated connection in full: if you set only CUBEJS_PRE_AGGREGATIONS_DB_HOST, the build connects to that host with the driver’s default user and password rather than the ones from CUBEJS_DB_USER and CUBEJS_DB_PASS.The one exception is the driver type: CUBEJS_PRE_AGGREGATIONS_DB_TYPE is ignored, since the dedicated connection always uses the same driver as the data source it belongs to.
CUBEJS_PRE_AGGREGATIONS_SCHEMA, CUBEJS_PRE_AGGREGATIONS_BUILDER, CUBEJS_PRE_AGGREGATIONS_BACKOFF_MAX_TIME, and CUBEJS_PRE_AGGREGATIONS_ALLOW_NON_STRICT_DATE_RANGE_MATCH share the prefix but configure pre-aggregation behavior rather than a connection, so they do not switch the data source onto a dedicated connection.
A custom driver_factory takes precedence over these variables: if both are configured, the driver_factory connection is used for pre-aggregations as well and a Pre-aggregation driver conflict warning is logged.

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Troubleshooting

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Refresh scheduler interval error

Sometimes, you might come across the following error:
It indicates that your refresh worker is overloaded. You probably have a lot of tenants, a lot of pre-aggregations to refresh, or both. If you’re using multitenancy, you’d need to deploy several Cube clusters (each one per a reduced set of tenants) so there will be multiple refresh workers which will work only on a subset of your tenants. If you’re using Cube Cloud, you can use a Multi-cluster deployment that would automatically do this for you.