presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/RaptorSplitManager.java/RaptorSplitManager/getSplits
class RaptorSplitManager:    @Override
    public ConnectorSplitSource getSplits(ConnectorTransactionHandle transaction, ConnectorSession session, ConnectorTableHandle handle, SplitSchedulingStrategy splitSchedulingStrategy)
    {
        RaptorTableHandle table = (RaptorTableHandle) handle;
        long tableId = table.getTableId();
        boolean bucketed = table.getBucketCount().isPresent();
        boolean merged = bucketed && !table.isDelete() && (table.getBucketCount().getAsInt() >= getOneSplitPerBucketThreshold(session));
        OptionalLong transactionId = table.getTransactionId();
        Optional<List<String>> bucketToNode = table.getBucketAssignments();
        verify(bucketed == bucketToNode.isPresent(), "mismatched bucketCount and bucketToNode presence");
        return new RaptorSplitSource(tableId, merged, table.getConstraint(), transactionId, bucketToNode);
    }