Fixed bug: inverted bool in DefaultRetryPolicy

The meaning of `data_present` was understood as the opposite in the
code.

Author: wprzytula

scylla/src/transport/retry_policy.rs

@@ -163,7 +163,7 @@ impl RetrySession for DefaultRetrySession {
             }
             // ReadTimeout - coordinator didn't receive enough replies in time.
             // Retry at most once and only if there were actually enough replies
-            // to satisfy consistency but they were all just checksums (data_present == true).
+            // to satisfy consistency but they were all just checksums (data_present == false).
             // This happens when the coordinator picked replicas that were overloaded/dying.
             // Retried request should have some useful response because the node will detect
             // that these replicas are dead.
@@ -176,7 +176,7 @@ impl RetrySession for DefaultRetrySession {
                 },
                 _,
             ) => {
-                if !self.was_read_timeout_retry && received >= required && *data_present {
+                if !self.was_read_timeout_retry && received >= required && !*data_present {
                     self.was_read_timeout_retry = true;
                     RetryDecision::RetrySameNode
                 } else {
@@ -374,61 +374,62 @@ mod tests {
     // On ReadTimeout we retry one time if there were enough responses and the data was present no matter the idempotence
     #[test]
     fn default_read_timeout() {
-        // Enough responses and data_present == true
-        let enough_responses_with_data = QueryError::DbError(
+        // Enough responses and data_present == false - coordinator received only checksums
+        let enough_responses_no_data = QueryError::DbError(
             DbError::ReadTimeout {
                 consistency: LegacyConsistency::Regular(Consistency::Two),
                 received: 2,
                 required: 2,
-                data_present: true,
+                data_present: false,
             },
             String::new(),
         );
 
         // Not idempotent
         let mut policy = DefaultRetryPolicy::new().new_session();
         assert_eq!(
-            policy.decide_should_retry(make_query_info(&enough_responses_with_data, false)),
+            policy.decide_should_retry(make_query_info(&enough_responses_no_data, false)),
             RetryDecision::RetrySameNode
         );
         assert_eq!(
-            policy.decide_should_retry(make_query_info(&enough_responses_with_data, false)),
+            policy.decide_should_retry(make_query_info(&enough_responses_no_data, false)),
             RetryDecision::DontRetry
         );
 
         // Idempotent
         let mut policy = DefaultRetryPolicy::new().new_session();
         assert_eq!(
-            policy.decide_should_retry(make_query_info(&enough_responses_with_data, true)),
+            policy.decide_should_retry(make_query_info(&enough_responses_no_data, true)),
             RetryDecision::RetrySameNode
         );
         assert_eq!(
-            policy.decide_should_retry(make_query_info(&enough_responses_with_data, true)),
+            policy.decide_should_retry(make_query_info(&enough_responses_no_data, true)),
             RetryDecision::DontRetry
         );
 
-        // Enough responses but data_present == false
-        let enough_responses_no_data = QueryError::DbError(
+        // Enough responses but data_present == true - coordinator probably timed out
+        // waiting for read-repair acknowledgement.
+        let enough_responses_with_data = QueryError::DbError(
             DbError::ReadTimeout {
                 consistency: LegacyConsistency::Regular(Consistency::Two),
                 received: 2,
                 required: 2,
-                data_present: false,
+                data_present: true,
             },
             String::new(),
         );
 
         // Not idempotent
         let mut policy = DefaultRetryPolicy::new().new_session();
         assert_eq!(
-            policy.decide_should_retry(make_query_info(&enough_responses_no_data, false)),
+            policy.decide_should_retry(make_query_info(&enough_responses_with_data, false)),
             RetryDecision::DontRetry
         );
 
         // Idempotent
         let mut policy = DefaultRetryPolicy::new().new_session();
         assert_eq!(
-            policy.decide_should_retry(make_query_info(&enough_responses_no_data, true)),
+            policy.decide_should_retry(make_query_info(&enough_responses_with_data, true)),
             RetryDecision::DontRetry
         );