MDEV-6156: Parallel replication incorrectly caches charset between worker threads

Replication caches the character sets used in a query, to be able to quickly
reuse them for the next query in the common case of them not having changed.

In parallel replication, this caching needs to be per-worker-thread. The
code was not modified to handle this correctly, so the caching in one worker
could cause another worker to run a query using the wrong character set,
causing replication corruption.

1 files changed, 11 insertions, 10 deletions

diff --git a/sql/rpl_rli.h b/sql/rpl_rli.h
index 48193afce4d..bcb237b6ced 100644
--- a/sql/rpl_rli.h
+++ b/sql/rpl_rli.h
@@ -295,7 +295,6 @@ public:
   /* Condition for UNTIL master_gtid_pos. */
   slave_connection_state until_gtid_pos;
 
-  char cached_charset[6];
   /*
     retried_trans is a cumulative counter: how many times the slave
     has retried a transaction (any) since slave started.
@@ -371,15 +370,6 @@ public:
 	    group_relay_log_pos);
   }
 
-  /*
-    Last charset (6 bytes) seen by slave SQL thread is cached here; it helps
-    the thread save 3 get_charset() per Query_log_event if the charset is not
-    changing from event to event (common situation).
-    When the 6 bytes are equal to 0 is used to mean "cache is invalidated".
-  */
-  void cached_charset_invalidate();
-  bool cached_charset_compare(char *charset) const;
-
   /**
     Helper function to do after statement completion.
 
@@ -546,6 +536,8 @@ struct rpl_group_info
   mysql_mutex_t sleep_lock;
   mysql_cond_t sleep_cond;
 
+  char cached_charset[6];
+
   /*
     trans_retries varies between 0 to slave_transaction_retries and counts how
     many times the slave has retried the present transaction; gets reset to 0
@@ -679,6 +671,15 @@ struct rpl_group_info
     return false;
   }
 
+  /*
+    Last charset (6 bytes) seen by slave SQL thread is cached here; it helps
+    the thread save 3 get_charset() per Query_log_event if the charset is not
+    changing from event to event (common situation).
+    When the 6 bytes are equal to 0 is used to mean "cache is invalidated".
+  */
+  void cached_charset_invalidate();
+  bool cached_charset_compare(char *charset) const;
+
   void clear_tables_to_lock();
   void cleanup_context(THD *, bool);
   void slave_close_thread_tables(THD *);