Package org.apache.ignite.table

Interface ContinuousQueryWatermark

All Superinterfaces:
Serializable
All Known Implementing Classes:
ContinuousQueryPhysicalTimeWatermark, ContinuousQueryTransactionWatermark
public interface ContinuousQueryWatermark extends Serializable
Continuous query watermark. Represents a starting point for a continuous query.

  • Method Details

    • ofInstant

      static ContinuousQueryWatermark ofInstant(Instant startTime)
      Creates a new watermark based on specified time (wall clock).

      The specified timestamp should not be older than now() - LowWatermarkConfiguration.dataAvailabilityTime(), or the query will fail with an exception.

      For example, to query 5 seconds in the past, use Instant.now().minusSeconds(5).

      Parameters:
      startTime - Start time.
      Returns:
      Watermark.

    • afterTransaction

      static ContinuousQueryWatermark afterTransaction(Transaction tx)
      Creates a new watermark based on a read-only transaction.

      This watermark provides a way to get a consistent view of all the existing data in the table and subscribe to any future updates. It guarantees that we either see a given row state as part of the initial query using the transaction, or as a continuous query event.

      Example usage: 

      
 Table table = ignite().tables().table("my-tbl");

 // Start a read-only transaction to get the initial state of the table.
 var txOpts = new TransactionOptions().readOnly(true);
 Transaction tx = ignite().transactions().begin(txOpts);

 Cursor<Tuple> initialQuery = table.recordView().query(tx, null);
 initialQuery.forEachRemaining(System.out::println);
 tx.commit();

 // Start a continuous query with a transaction watermark to get all updates since the initial query.
 var wm = ContinuousQueryWatermark.afterTransaction(tx);
 var cqOpts = ContinuousQueryOptions.builder().watermark(wm).build();
 table.recordView().queryContinuously(new MySubscriber<Tuple>(), cqOpts);
      Parameters:
      tx - Transaction.
      Returns:
      Watermark.