[GitHub] tweise commented on a change in pull request #6980: [FLINK-5697] [kinesis] Add periodic per-shard watermark support

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tweise commented on a change in pull request #6980: [FLINK-5697] [kinesis] Add periodic per-shard watermark support
URL: https://github.com/apache/flink/pull/6980#discussion_r235149070
 
 

 ##########
 File path: flink-connectors/flink-connector-kinesis/src/main/java/org/apache/flink/streaming/connectors/kinesis/internals/KinesisDataFetcher.java
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 @@ -609,7 +667,115 @@ public int registerNewSubscribedShardState(KinesisStreamShardState newSubscribed
 				this.numberOfActiveShards.incrementAndGet();
 			}
 
-			return subscribedShardsState.size() - 1;
+			int shardStateIndex = subscribedShardsState.size() - 1;
+
+			// track all discovered shards for watermark determination
+			ShardWatermarkState sws = shardWatermarks.get(shardStateIndex);
+			if (sws == null) {
+				sws = new ShardWatermarkState();
+				try {
+					sws.periodicWatermarkAssigner = InstantiationUtil.clone(periodicWatermarkAssigner);
+				} catch (Exception e) {
+					throw new RuntimeException(e);
+				}
+				sws.lastUpdated = getCurrentTimeMillis();
+				sws.lastRecordTimestamp = Long.MIN_VALUE;
+				shardWatermarks.put(shardStateIndex, sws);
+			}
+
+			return shardStateIndex;
+		}
+	}
+
+	/**
+	 * Return the current system time. Allow tests to override this to simulate progress for watermark
+	 * logic.
+	 *
+	 * @return
+	 */
+	@VisibleForTesting
+	protected long getCurrentTimeMillis() {
+		return System.currentTimeMillis();
+	}
+
+	/**
+	 * Called periodically to emit a watermark. Checks all shards for the current event time
+	 * watermark, and possibly emits the next watermark.
+	 *
+	 * <p>Shards that have not received an update for a certain interval are considered inactive so as
+	 * to not hold back the watermark indefinitely. When all shards are inactive, the subtask will be
+	 * marked as temporarily idle to not block downstream operators.
+	 */
+	@VisibleForTesting
+	protected void emitWatermark() {
+		LOG.debug(
+			"###evaluating watermark for subtask {} time {}",
+			indexOfThisConsumerSubtask,
+			getCurrentTimeMillis());
+		long potentialWatermark = Long.MAX_VALUE;
+		long idleTime =
+			(shardIdleIntervalMillis > 0)
+				? getCurrentTimeMillis() - shardIdleIntervalMillis
+				: Long.MAX_VALUE;
+
+		for (Map.Entry<Integer, ShardWatermarkState> e : shardWatermarks.entrySet()) {
+			// consider only active shards, or those that would advance the watermark
+			Watermark w = e.getValue().periodicWatermarkAssigner.getCurrentWatermark();
+			if (w != null && (e.getValue().lastUpdated >= idleTime || w.getTimestamp() > lastWatermark)) {
+				potentialWatermark = Math.min(potentialWatermark, w.getTimestamp());
+			}
+		}
+
+		// advance watermark if possible (watermarks can only be ascending)
+		if (potentialWatermark == Long.MAX_VALUE) {
 
 Review comment:
   The potential watermark depends on the logic in the prior loop. The idle condition should only be executed when there is no potential watermark.

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