This is the second advantage post to understand how Storm SQL leverages Calcite. See the previous post here:

• How Storm SQL is executed
• Query Explain with Calcite

Compared Explain and Submit function in How Storm SQL is executed, the execution plan generated doesn’t match:

// explain function
RelNode tree = planner.convert(validate);

// submit function
TridentRel relNode = getPlan(query);

This is the core part, about how Storm SQL leverages Calcite’s parser engine, and plugin its own planner.

To simplify, customized rules convert standard RelOpt into Storm-alien RelOpt.

ConverterRule
ConverterRule defines a rule which converts from one calling convertion to another without Semantics.

Take TridentScanRule for example:

public class TridentScanRule extends ConverterRule {
  public static final TridentScanRule INSTANCE = new TridentScanRule();
  public static final int DEFAULT_PARALLELISM_HINT = 1;

  private TridentScanRule() {
    super(EnumerableTableScan.class, EnumerableConvention.INSTANCE, TridentLogicalConvention.INSTANCE, "TridentScanRule");
  }

  @Override
  public RelNode convert(RelNode rel) {
    final TableScan scan = (TableScan) rel;
    int parallelismHint = DEFAULT_PARALLELISM_HINT;

    final ParallelStreamableTable parallelTable = scan.getTable().unwrap(ParallelStreamableTable.class);
    if (parallelTable != null && parallelTable.parallelismHint() != null) {
      parallelismHint = parallelTable.parallelismHint();
    }

    final Table table = scan.getTable().unwrap(Table.class);
    switch (table.getJdbcTableType()) {
      case STREAM:
        return new TridentStreamScanRel(scan.getCluster(),
            scan.getTraitSet().replace(TridentLogicalConvention.INSTANCE),
            scan.getTable(), parallelismHint);
      default:
        throw new IllegalArgumentException(String.format("Unsupported table type: %s", table.getJdbcTableType()));
    }
  }
}

In this class, TridentScanRule converts a EnumerableTableScan to TridentStreamScanRel.

With this way, Storm defines its own RelNode, and use to tridentPlan to create a TridentTopology.