START_REFRESH
For the current schema, transfers data to projections that are not able to participate in query execution due to missing or out-of-date data.
Syntax
START_REFRESH()
Notes
- If you want to refresh only the projections in a specific table, use REFRESH.
- Unlike REFRESH(), which runs in the foreground of the caller's session, START_REFRESH() runs in the background.
- When a design is deployed through the Database Designer, it is automatically refreshed. See Deploying a Design in the Administrator's Guide.
- All nodes must be up in order to start a refresh.
- START_REFRESH() has no effect if a refresh is already running.
- The refresh runs asynchronously.
- Shutting down the database ends the refresh.
- To view the progress of the refresh, see the PROJECTION_REFRESHES and PROJECTIONS system tables.
- If a projection is updated from scratch, the data stored in the projection represents the table columns as of the epoch in which the refresh commits. As a result, the query optimizer might not choose the new projection for AT EPOCH queries that request historical data at epochs older than the refresh epoch of the projection. Projections refreshed from buddies retain history and can be used to answer historical queries.
Privileges
None
Example
The following command starts the refresh operation:
=> SELECT START_REFRESH(); start_refresh ---------------------------------------- Starting refresh background process.