MDEV-15132 Avoid accessing the TRX_SYS page

trx_write_serialisation_history(): Only invoke trx_sysf_get() to exclusively lock the TRX_SYS page if some change really has to be written to the page. On transaction commit, we will still write some binlog and Galera WSREP XID information. FIXME: If this information has to be written, it should be partitioned into the rollback segment pages.

Author: dr-m

storage/innobase/trx/trx0trx.cc

@@ -1336,20 +1336,28 @@ trx_write_serialisation_history(
 
 MONITOR_INC(MONITOR_TRX_COMMIT_UNDO);
 
+#ifdef WITH_WSREP
+const bool update_wsrep = wsrep_is_wsrep_xid(trx->xid);
+#endif
+const bool update_binlog_pos = trx->mysql_log_file_name
+&& *trx->mysql_log_file_name;
+if (!update_binlog_pos
+#ifdef WITH_WSREP
+ && !update_wsrep
+#endif
+ ) return true;
+
 buf_block_t* block = trx_sysf_get(mtr);
 #ifdef WITH_WSREP
-/* Update latest MySQL wsrep XID in trx sys header. */
-if (wsrep_is_wsrep_xid(trx->xid)) {
+if (update_wsrep)
 trx_sys_update_wsrep_checkpoint(trx->xid, block, mtr);
-}
 #endif /* WITH_WSREP */
 
 /* Update the latest MySQL binlog name and offset info
 in trx sys header if MySQL binlogging is on or the database
 server is a MySQL replication slave */
 
-if (trx->mysql_log_file_name != NULL
- && trx->mysql_log_file_name[0] != '\0') {
+if (update_binlog_pos) {
 
 trx_sys_update_mysql_binlog_offset(
 trx->mysql_log_file_name,