MDEV-5262: Missing retry after temp error in parallel replication

Start implementing that an event group can be re-tried in parallel replication
if it fails with a temporary error (like deadlock).

Patch is very incomplete, just some very basic retry works.

Stuff still missing (not complete list):

 - Handle moving to the next relay log file, if event group to be retried
   spans multiple relay log files.

 - Handle refcounting of relay log files, to ensure that we do not purge a
   relay log file and then later attempt to re-execute events out of it.

 - Handle description_event_for_exec - we need to save this somehow for the
   possible retry - and use the correct one in case it differs between relay
   logs.

 - Do another retry attempt in case the first retry also fails.

 - Limit the max number of retries.

 - Lots of testing will be needed for the various edge cases.

1 files changed, 5 insertions, 1 deletions

diff --git a/sql/rpl_parallel.h b/sql/rpl_parallel.h
index 1808efd0926..3b6641523f6 100644
--- a/sql/rpl_parallel.h
+++ b/sql/rpl_parallel.h
@@ -106,11 +106,15 @@ struct rpl_parallel_thread {
     queued_size-= dequeue_size;
   }
 
+  queued_event *get_qev_common(Log_event *ev, ulonglong event_size);
   queued_event *get_qev(Log_event *ev, ulonglong event_size,
                         Relay_log_info *rli);
+  queued_event *retry_get_qev(Log_event *ev, queued_event *orig_qev,
+                              const char *relay_log_name,
+                              ulonglong event_pos, ulonglong event_size);
   void free_qev(queued_event *qev);
   rpl_group_info *get_rgi(Relay_log_info *rli, Gtid_log_event *gtid_ev,
-                          rpl_parallel_entry *e);
+                          rpl_parallel_entry *e, ulonglong event_size);
   void free_rgi(rpl_group_info *rgi);
   group_commit_orderer *get_gco(uint64 wait_count, group_commit_orderer *prev);
   void free_gco(group_commit_orderer *gco);