[yugabyte#14163] yql - Improve error message and logging in case of i…

…ndex read error

Summary:
Previously we would show the same error message indicating a unique constraint error any time a
unique index operation failed. This revision improves the logging and error message surfaced by
including the remove error to the client.

Test Plan: Jenkins

Reviewers: pjain, amitanand

Differential Revision: http://phabricator.dev.yugabyte.com/D20063

src/yb/docdb/cql_operation.cc

@@ -1414,6 +1414,7 @@ Result<QLWriteRequestPB*> CreateAndSetupIndexInsertRequest(
     RETURN_NOT_OK(expr_executor->EvalCondition(
       index->where_predicate_spec()->where_expr().condition(), new_row,
       &new_row_satisfies_idx_pred));
+    VLOG(1) << "Eval condition on partial index " << new_row_satisfies_idx_pred;
     if (index_pred_new_row) {
       *index_pred_new_row = new_row_satisfies_idx_pred;
     }

src/yb/tablet/write_query.cc

@@ -87,7 +87,7 @@ bool CheckSchemaVersion(
     return true;
   }
 
-  DVLOG(1) << " On " << table_info->table_name
+  VLOG(1) << " On " << table_info->table_name
            << " Setting status for write as YQL_STATUS_SCHEMA_VERSION_MISMATCH tserver's: "
            << table_info->schema_version << " vs req's : " << schema_version
            << " is req compatible with prev version: "
@@ -310,7 +310,7 @@ Result<bool> WriteQuery::CqlPrepareExecute() {
   RETURN_NOT_OK(InitExecute(ExecuteMode::kCql));
 
   auto& metadata = *tablet().metadata();
-  DVLOG(2) << "Schema version for  " << metadata.table_name() << ": " << metadata.schema_version();
+  VLOG(2) << "Schema version for  " << metadata.table_name() << ": " << metadata.schema_version();
 
   if (!CqlCheckSchemaVersion()) {
     return false;
@@ -684,12 +684,15 @@ void WriteQuery::CompleteQLWriteBatch(const Status& status) {
         ql_write_op->request().type() == QLWriteRequestPB::QL_STMT_INSERT &&
         ql_write_op->response()->has_applied() && !ql_write_op->response()->applied()) {
       // If this is an insert into a unique index and it fails to apply, report duplicate value err.
-      ql_write_op->response()->set_status(QLResponsePB::YQL_STATUS_USAGE_ERROR);
+      // has_applied is only true if we have evaluated the requests if_expr and is only false if
+      // that if_expr ws not satisfied or if the remote index was unique and had a duplicate value
+      // to the one we're trying to insert here.
+      VLOG(1) << "Could not apply operation to remote index " << AsString(ql_write_op->request())
+               << " due to " << AsString(ql_write_op->response());
       ql_write_op->response()->set_error_message(
           Format("Duplicate value disallowed by unique index $0",
           tablet().metadata()->table_name()));
-      DVLOG(1) << "Could not apply the given operation " << AsString(ql_write_op->request())
-               << " due to " << AsString(ql_write_op->response());
+      ql_write_op->response()->set_status(QLResponsePB::YQL_STATUS_USAGE_ERROR);
     } else if (ql_write_op->rowblock() != nullptr) {
       // If the QL write op returns a rowblock, move the op to the transaction state to return the
       // rows data as a sidecar after the transaction completes.
@@ -811,7 +814,8 @@ void WriteQuery::UpdateQLIndexesFlushed(
     auto* index_response = index_op->mutable_response();
 
     if (index_response->status() != QLResponsePB::YQL_STATUS_OK) {
-      DVLOG(1) << "Got status " << index_response->status() << " for " << AsString(index_op);
+      VLOG(1) << "Got response " << index_response->ShortDebugString()
+              << " for " << AsString(index_op);
       response->set_status(index_response->status());
       response->set_error_message(std::move(*index_response->mutable_error_message()));
     }