MDEV-11179: WSREP transaction excceded size limit in Galera cluster

... causes MariaDB to crash

On error, the wsrep replication buffer (binlog) is dumped to a file
to aid investigations. In order to also include the binlog header,
FDLE object is also needed. This object is only available for wsrep-
threads.
Fix: Instantiate an FDLE object for non-wsrep threads.

Author: Nirbhay Choubey

sql/wsrep_applier.cc

@@ -73,6 +73,9 @@ Format_description_log_event* wsrep_get_apply_format(THD* thd)
   {
     return (Format_description_log_event*) thd->wsrep_apply_format;
   }
+
+  DBUG_ASSERT(thd->wsrep_rgi);
+
   return thd->wsrep_rgi->rli->relay_log.description_event_for_exec;
 }
 

sql/wsrep_binlog.cc

@@ -442,11 +442,13 @@ void thd_binlog_flush_pending_rows_event(THD *thd, bool stmt_end)
 void wsrep_dump_rbr_buf_with_header(THD *thd, const void *rbr_buf,
                                     size_t buf_len)
 {
+  DBUG_ENTER("wsrep_dump_rbr_buf_with_header");
+
   char filename[PATH_MAX]= {0};
   File file;
   IO_CACHE cache;
   Log_event_writer writer(&cache);
-  Format_description_log_event *ev= wsrep_get_apply_format(thd);
+  Format_description_log_event *ev;
 
   int len= my_snprintf(filename, PATH_MAX, "%s/GRA_%ld_%lld_v2.log",
                        wsrep_data_home_dir, thd->thread_id,
@@ -455,7 +457,7 @@ void wsrep_dump_rbr_buf_with_header(THD *thd, const void *rbr_buf,
   if (len >= PATH_MAX)
   {
     WSREP_ERROR("RBR dump path too long: %d, skipping dump.", len);
-    return;
+    DBUG_VOID_RETURN;
   }
 
   if ((file= mysql_file_open(key_file_wsrep_gra_log, filename,
@@ -477,6 +479,13 @@ void wsrep_dump_rbr_buf_with_header(THD *thd, const void *rbr_buf,
     goto cleanup2;
   }
 
+  /*
+    Instantiate an FDLE object for non-wsrep threads (to be written
+    to the dump file).
+  */
+  ev= (thd->wsrep_applier) ? wsrep_get_apply_format(thd) :
+    (new Format_description_log_event(4));
+
   if (writer.write(ev) || my_b_write(&cache, (uchar*)rbr_buf, buf_len) ||
       flush_io_cache(&cache))
   {
@@ -489,5 +498,9 @@ void wsrep_dump_rbr_buf_with_header(THD *thd, const void *rbr_buf,
 
 cleanup1:
   mysql_file_close(file, MYF(MY_WME));
+
+  if (!thd->wsrep_applier) delete ev;
+
+  DBUG_VOID_RETURN;
 }