skip tsdb snapshot apply if has not receive new ddl change from last snapshot time

parse/src/main/java/com/alibaba/otter/canal/parse/inbound/mysql/tsdb/DatabaseTableMeta.java

@@ -63,6 +63,7 @@ public class DatabaseTableMeta implements TableMetaTSDB {
     private CanalEventFilter          filter;
     private CanalEventFilter          blackFilter;
     private EntryPosition             lastPosition;
+    private boolean                   hasNewDdl;
     private MetaHistoryDAO            metaHistoryDAO;
     private MetaSnapshotDAO           metaSnapshotDAO;
     private int                       snapshotInterval = 24;
@@ -139,6 +140,7 @@ public class DatabaseTableMeta implements TableMetaTSDB {
         synchronized (memoryTableMeta) {
             if (memoryTableMeta.apply(position, schema, ddl, extra)) {
                 this.lastPosition = position;
+                this.hasNewDdl = true;
                 // 同步每次变更给远程做历史记录
                 return applyHistoryToDB(position, schema, ddl, extra);
             } else {
@@ -270,10 +272,11 @@ public class DatabaseTableMeta implements TableMetaTSDB {
         MemoryTableMeta tmpMemoryTableMeta = new MemoryTableMeta();
         Map<String, String> schemaDdls = null;
         synchronized (memoryTableMeta) {
-            if (!init && position == null) {
+            if (!init && !hasNewDdl) {
                 // 如果是持续构建,则识别一下是否有DDL变更过,如果没有就忽略了
                 return false;
             }
+            this.hasNewDdl = false;
             schemaDdls = memoryTableMeta.snapshot();
             for (Map.Entry<String, String> entry : schemaDdls.entrySet()) {
                 tmpMemoryTableMeta.apply(position, entry.getKey(), entry.getValue(), null);