Constraints

Constraints are rules that enforce data integrity in a database. Spice supports constraints on locally accelerated tables to ensure data quality, as well as configuring the behavior for inserting data updates that violate constraints.

Constraints are specified in the Spicepod via the primary_key field in the acceleration configuration. Additional unique constraints are specified via the indexes field with the value unique.

The behavior of inserting data that violates the constraint can be configured via the on_conflict field to either drop the data that violates the constraint or upsert that data into the accelerated table (i.e. update all values other than the columns that are part of the constraint to match the incoming data).

If there are multiple rows in the incoming data that violate any constraint, the entire incoming batch of data will be dropped.

Example Spicepod:

datasets:
  - from: spice.ai/eth.recent_blocks
    name: eth.recent_blocks
    acceleration:
      enabled: true
      engine: sqlite
      primary_key: hash # Define a primary key on the `hash` column
      indexes:
        '(number, timestamp)': unique # Add a unique index with a multicolumn key comprised of the `number` and `timestamp` columns
      on_conflict:
        # Upsert the incoming data when the primary key constraint on "hash" is violated,
        # alternatively "drop" can be used instead of "upsert" to drop the data update.
        hash: upsert

Column References

Column references can be used to specify which columns are part of the constraint. The column reference can be a single column name or a multicolumn key. The column reference must be enclosed in parentheses if it is a multicolumn key.

Examples

• number: Reference a constraint on the number column
• (hash, timestamp): Reference a constraint on the hash and timestamp columns

Limitations

• Not supported for in-memory Arrow: The default in-memory Arrow acceleration engine does not support constraints. Use DuckDB, SQLite, or PostgreSQL as the acceleration engine to enable constraint checking.

• Single on_conflict target supported: Only a single on_conflict target can be specified, unless all on_conflict targets are specified with drop.

  • Examples for valid/invalid on_conflict targets

    The following Spicepod is invalid because it specifies multiple on_conflict targets with upsert:

    Invalid

    datasets:
    
    - from: spice.ai/eth.recent_blocks
      name: eth.recent_blocks
      acceleration:
      enabled: true
      engine: sqlite
      primary_key: hash
      indexes:
      "(number, timestamp)": unique
      on_conflict:
      hash: upsert
      "(number, timestamp)": upsert

    The following Spicepod is valid because it specifies multiple on_conflict targets with drop, which is allowed:

    Valid

    datasets:
    
    - from: spice.ai/eth.recent_blocks
      name: eth.recent_blocks
      acceleration:
      enabled: true
      engine: sqlite
      primary_key: hash
      indexes:
      "(number, timestamp)": unique
      on_conflict:
      hash: drop
      "(number, timestamp)": drop

    The following Spicepod is invalid because it specifies multiple on_conflict targets with upsert and drop:

    Invalid

    datasets:
    
    - from: spice.ai/eth.recent_blocks
    name: eth.recent_blocks
    acceleration:
    enabled: true
    engine: sqlite
    primary_key: hash
    indexes:
    "(number, timestamp)": unique
    on_conflict:
    hash: upsert
    "(number, timestamp)": drop

• DuckDB Limitations:

  • DuckDB does not support upsert for datasets with List or Map types.

  • Standard indexes unexpectedly act like unique indexes and block updates when upsert is configured.

    • Standard indexes blocking updates

      The following Spicepod specifies a standard index on the number column, which blocks updates when upsert is configured for the hash column:

      datasets:
        - from: spice.ai/eth.recent_blocks
          name: eth.recent_blocks
          acceleration:
            enabled: true
            engine: duckdb
            primary_key: hash
            indexes:
              number: enabled
            on_conflict:
              hash: upsert

      The following error is returned when attempting to upsert data into the eth.recent_blocks table:

      ERROR runtime::accelerated_table::refresh: Error adding data for eth.recent_blocks: External error:
      Unable to insert into duckdb table: Binder Error: Can not assign to column 'number' because
      it has a UNIQUE/PRIMARY KEY constraint

      This is a limitation in DuckDB.