[GitHub] [iotdb] jt2594838 commented on a change in pull request #2766: [IOTDB-1118] [Distributed] Limit query log lag in mid consistency level

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jt2594838 commented on a change in pull request #2766:
URL: https://github.com/apache/iotdb/pull/2766#discussion_r587987308



##########
File path: cluster/src/assembly/resources/conf/iotdb-cluster.properties
##########
@@ -148,4 +148,8 @@ enable_use_persist_log_on_disk_to_catch_up=true
 
 # The number of logs read on the disk at one time, which is mainly used to control the memory usage.
 # This value multiplied by the log size is about the amount of memory used to read logs from the disk at one time.
-max_number_of_logs_per_fetch_on_disk=1000
\ No newline at end of file
+max_number_of_logs_per_fetch_on_disk=1000
+
+# When consistency level set to mid, query failed if the log lag exceeds max_read_log_lag
+# This default value is 1000
+max_read_log_lag=1000

Review comment:
       Yes, at least we can supplement that one log corresponds to one client operation.

##########
File path: cluster/src/main/java/org/apache/iotdb/cluster/server/member/RaftMember.java
##########
@@ -731,28 +730,70 @@ public TSStatus executeNonQueryPlan(ExecutNonQueryReq request)
   public void syncLeaderWithConsistencyCheck(boolean isWriteRequest)
       throws CheckConsistencyException {
     if (isWriteRequest) {
-      if (!syncLeader()) {
-        throw CheckConsistencyException.CHECK_STRONG_CONSISTENCY_EXCEPTION;
-      }
+      syncLeader(new StrongCheckConsistency());
     } else {
-      switch (ClusterDescriptor.getInstance().getConfig().getConsistencyLevel()) {
+      switch (config.getConsistencyLevel()) {
         case STRONG_CONSISTENCY:
-          if (!syncLeader()) {
-            throw CheckConsistencyException.CHECK_STRONG_CONSISTENCY_EXCEPTION;
-          }
+          syncLeader(new StrongCheckConsistency());
           return;
         case MID_CONSISTENCY:
-          // do not care success or not
-          syncLeader();
+          // if leaderCommitId bigger than localAppliedId a value,
+          // will throw CHECK_MID_CONSISTENCY_EXCEPTION
+          syncLeader(
+              new CheckConsistency() {

Review comment:
       But I do not think it is necessary to `new` each time the method is called, as they are not changed throughout the process. Maybe you can make them static members of a class. 




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