[mysql] Optimization that skips the binlog read if the low watermark equals high watermark

flink-connector-mysql-cdc/src/main/java/com/ververica/cdc/connectors/mysql/debezium/reader/SnapshotSplitReader.java

@@ -22,6 +22,7 @@ import org.apache.flink.util.FlinkRuntimeException;
 
 import org.apache.flink.shaded.guava18.com.google.common.util.concurrent.ThreadFactoryBuilder;
 
+import com.ververica.cdc.connectors.mysql.debezium.dispatcher.SignalEventDispatcher;
 import com.ververica.cdc.connectors.mysql.debezium.task.MySqlBinlogSplitReadTask;
 import com.ververica.cdc.connectors.mysql.debezium.task.MySqlSnapshotSplitReadTask;
 import com.ververica.cdc.connectors.mysql.debezium.task.context.StatefulTaskContext;
@@ -114,42 +115,25 @@ public class SnapshotSplitReader implements DebeziumReader<SourceRecord, MySqlSp
                         SnapshotResult snapshotResult =
                                 splitSnapshotReadTask.execute(sourceContext);
 
-                        final MySqlBinlogSplit appendBinlogSplit = createBinlogSplit(sourceContext);
-                        final MySqlOffsetContext mySqlOffsetContext =
-                                statefulTaskContext.getOffsetContext();
-                        mySqlOffsetContext.setBinlogStartPoint(
-                                appendBinlogSplit.getStartingOffset().getFilename(),
-                                appendBinlogSplit.getStartingOffset().getPosition());
+                        final MySqlBinlogSplit backfillBinlogSplit =
+                                createBackfillBinlogSplit(sourceContext);
+                        // optimization that skip the binlog read when the low watermark equals high
+                        // watermark
+                        final boolean binlogBackfillRequired =
+                                backfillBinlogSplit
+                                        .getEndingOffset()
+                                        .isBefore(backfillBinlogSplit.getStartingOffset());
+                        if (!binlogBackfillRequired) {
+                            dispatchHighWatermark(backfillBinlogSplit);
+                            currentTaskRunning = false;
+                            return;
+                        }
+
                         // execute binlog read task
                         if (snapshotResult.isCompletedOrSkipped()) {
-                            // we should only capture events for the current table,
-                            // otherwise, we may can't find corresponding schema
-                            Configuration dezConf =
-                                    statefulTaskContext
-                                            .getDezConf()
-                                            .edit()
-                                            .with(
-                                                    "table.whitelist",
-                                                    currentSnapshotSplit.getTableId())
-                                            .build();
-                            // task to read binlog for current split
-                            MySqlBinlogSplitReadTask splitBinlogReadTask =
-                                    new MySqlBinlogSplitReadTask(
-                                            new MySqlConnectorConfig(dezConf),
-                                            mySqlOffsetContext,
-                                            statefulTaskContext.getConnection(),
-                                            statefulTaskContext.getDispatcher(),
-                                            statefulTaskContext.getErrorHandler(),
-                                            StatefulTaskContext.getClock(),
-                                            statefulTaskContext.getTaskContext(),
-                                            (MySqlStreamingChangeEventSourceMetrics)
-                                                    statefulTaskContext
-                                                            .getStreamingChangeEventSourceMetrics(),
-                                            statefulTaskContext
-                                                    .getTopicSelector()
-                                                    .getPrimaryTopic(),
-                                            appendBinlogSplit);
-                            splitBinlogReadTask.execute(
+                            final MySqlBinlogSplitReadTask backfillBinlogReadTask =
+                                    createBackfillBinlogReadTask(backfillBinlogSplit);
+                            backfillBinlogReadTask.execute(
                                     new SnapshotBinlogSplitChangeEventSourceContextImpl());
                         } else {
                             readException =
@@ -170,7 +154,7 @@ public class SnapshotSplitReader implements DebeziumReader<SourceRecord, MySqlSp
                 });
     }
 
-    private MySqlBinlogSplit createBinlogSplit(
+    private MySqlBinlogSplit createBackfillBinlogSplit(
             SnapshotSplitChangeEventSourceContextImpl sourceContext) {
         return new MySqlBinlogSplit(
                 currentSnapshotSplit.splitId(),
@@ -181,6 +165,49 @@ public class SnapshotSplitReader implements DebeziumReader<SourceRecord, MySqlSp
                 currentSnapshotSplit.getTableSchemas());
     }
 
+    private MySqlBinlogSplitReadTask createBackfillBinlogReadTask(
+            MySqlBinlogSplit backfillBinlogSplit) {
+        final MySqlOffsetContext.Loader loader =
+                new MySqlOffsetContext.Loader(statefulTaskContext.getConnectorConfig());
+        final MySqlOffsetContext mySqlOffsetContext =
+                (MySqlOffsetContext)
+                        loader.load(backfillBinlogSplit.getStartingOffset().getOffset());
+        // we should only capture events for the current table,
+        // otherwise, we may can't find corresponding schema
+        Configuration dezConf =
+                statefulTaskContext
+                        .getDezConf()
+                        .edit()
+                        .with("table.whitelist", currentSnapshotSplit.getTableId())
+                        .build();
+        // task to read binlog and backfill for current split
+        return new MySqlBinlogSplitReadTask(
+                new MySqlConnectorConfig(dezConf),
+                mySqlOffsetContext,
+                statefulTaskContext.getConnection(),
+                statefulTaskContext.getDispatcher(),
+                statefulTaskContext.getErrorHandler(),
+                StatefulTaskContext.getClock(),
+                statefulTaskContext.getTaskContext(),
+                (MySqlStreamingChangeEventSourceMetrics)
+                        statefulTaskContext.getStreamingChangeEventSourceMetrics(),
+                statefulTaskContext.getTopicSelector().getPrimaryTopic(),
+                backfillBinlogSplit);
+    }
+
+    private void dispatchHighWatermark(MySqlBinlogSplit backFillBinlogSplit)
+            throws InterruptedException {
+        final SignalEventDispatcher signalEventDispatcher =
+                new SignalEventDispatcher(
+                        statefulTaskContext.getOffsetContext().getPartition(),
+                        statefulTaskContext.getTopicSelector().getPrimaryTopic(),
+                        statefulTaskContext.getDispatcher().getQueue());
+        signalEventDispatcher.dispatchWatermarkEvent(
+                backFillBinlogSplit,
+                backFillBinlogSplit.getEndingOffset(),
+                SignalEventDispatcher.WatermarkKind.BINLOG_END);
+    }
+
     @Override
     public boolean isFinished() {
         return currentSnapshotSplit == null