MDEV-4506: Parallel replication. Intermediate commit.

Implement facility for the commit in one thread to wait for the commit of
another to complete first. The wait is done in a way that does not hinder
that a waiter and a waitee can group commit together with a single fsync()
in both binlog and InnoDB. The wait is done efficiently with respect to
locking.

The patch was originally made to support TaoBao parallel replication with
in-order commit; now it will be adapted to also be used for parallel
replication of group-committed transactions.

A waiter THD registers itself with a prior waitee THD. The waiter will then
complete its commit at the earliest in the same group commit of the waitee
(when using binlog). The wait can also be done explicitly by the waitee.

1 files changed, 8 insertions, 0 deletions

diff --git a/sql/handler.cc b/sql/handler.cc
index 660697cd74b..25b2ee13187 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -1455,6 +1455,8 @@ int ha_commit_one_phase(THD *thd, bool all)
   */
   bool is_real_trans=all || thd->transaction.all.ha_list == 0;
   DBUG_ENTER("ha_commit_one_phase");
+  if (is_real_trans)
+    thd->wait_for_prior_commit();
   int res= commit_one_phase_2(thd, all, trans, is_real_trans);
   DBUG_RETURN(res);
 }
@@ -1494,7 +1496,10 @@ commit_one_phase_2(THD *thd, bool all, THD_TRANS *trans, bool is_real_trans)
   }
   /* Free resources and perform other cleanup even for 'empty' transactions. */
   if (is_real_trans)
+  {
+    thd->wakeup_subsequent_commits();
     thd->transaction.cleanup();
+  }
 
   DBUG_RETURN(error);
 }
@@ -1569,7 +1574,10 @@ int ha_rollback_trans(THD *thd, bool all)
   }
   /* Always cleanup. Even if nht==0. There may be savepoints. */
   if (is_real_trans)
+  {
+    thd->wakeup_subsequent_commits();
     thd->transaction.cleanup();
+  }
   if (all)
     thd->transaction_rollback_request= FALSE;