[BugFix] Fix BE crash when schema scan rpc failed (backport #51889)

be/src/exec/pipeline/scan/scan_operator.cpp

@@ -424,8 +424,11 @@ Status ScanOperator::_trigger_next_scan(RuntimeState* state, int chunk_source_in
  << print_id(state->fragment_instance_id()) << ", error=" << start_status.to_string();
  _set_scan_status(start_status);
  }
+ Status status;
 
- auto status = chunk_source->buffer_next_batch_chunks_blocking(state, kIOTaskBatchSize, _workgroup.get());
+ if (start_status.ok()) {
+ status = chunk_source->buffer_next_batch_chunks_blocking(state, kIOTaskBatchSize, _workgroup.get());
+ }
 
  if (!status.ok() && !status.is_end_of_file()) {
  LOG(ERROR) << "scan fragment " << print_id(state->fragment_instance_id()) << " driver "

be/src/exec/schema_scanner/schema_variables_scanner.cpp

@@ -18,8 +18,10 @@
 #include "runtime/runtime_state.h"
 #include "runtime/string_value.h"
 #include "types/logical_type.h"
+#include "util/failpoint/fail_point.h"
 
 namespace starrocks {
+DEFINE_FAIL_POINT(schema_scan_rpc_failed);
 
 SchemaScanner::ColumnDesc SchemaVariablesScanner::_s_vars_columns[] = {
  // name, type, size
@@ -57,6 +59,7 @@ Status SchemaVariablesScanner::start(RuntimeState* state) {
  var_params.__set_threadId(_param->thread_id);
 
  // init schema scanner state
+ FAIL_POINT_TRIGGER_RETURN_ERROR(schema_scan_rpc_failed);
  RETURN_IF_ERROR(SchemaScanner::init_schema_scanner_state(state));
  RETURN_IF_ERROR(SchemaHelper::show_variables(_ss_state, var_params, &_var_result));
 

test/sql/test_scan/R/test_schema_scan_rpc_failed

@@ -0,0 +1,10 @@
+-- name: test_schema_scan_rpc_failed
+admin enable failpoint 'schema_scan_rpc_failed';
+-- result:
+-- !result
+[UC] SHOW VARIABLES WHERE Variable_name ='language';
+-- result:
+-- !result
+admin disable failpoint 'schema_scan_rpc_failed';
+-- result:
+-- !result

test/sql/test_scan/T/test_schema_scan_rpc_failed

@@ -0,0 +1,5 @@
+-- name: test_schema_scan_rpc_failed
+
+admin enable failpoint 'schema_scan_rpc_failed';
+[UC] SHOW VARIABLES WHERE Variable_name ='language';
+admin disable failpoint 'schema_scan_rpc_failed';