Making FLUSH TABLES WITH READ LOCK block COMMITs of existing transactions,

in a deadlock-free manner. This splits locking the global read lock in two steps.
This fixes a consequence of this bug, known as:
BUG#4953 'mysqldump --master-data may report incorrect binlog position if using InnoDB'
And a test.


sql/handler.cc:
  making COMMIT wait if FLUSH TABLES WITH READ LOCK happened.
sql/lock.cc:
  an additional stage so that FLUSH TABLES WITH READ LOCK blocks COMMIT:
  make_global_read_lock_block_commit():
  taking the global read lock is TWO steps (2nd step is optional; without
  it, COMMIT of existing transactions will be allowed):
  lock_global_read_lock() THEN make_global_read_lock_block_commit().
sql/mysql_priv.h:
  new argument to wait_if_global_read_lock()
sql/sql_class.h:
  THD::global_read_lock now an uint to reflect the 2 steps of global read lock (does not block COMMIT / does)
sql/sql_db.cc:
  update for new prototype
sql/sql_parse.cc:
  implementing the two steps of global read lock so that FLUSH TABLES WITH READ LOCK can block COMMIT without deadlocking with COMMITs.

1 files changed, 23 insertions, 8 deletions

diff --git a/sql/handler.cc b/sql/handler.cc
index a1e738583fd..9eb129fab45 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -342,17 +342,30 @@ int ha_commit_trans(THD *thd, THD_TRANS* trans)
 #ifdef USING_TRANSACTIONS
   if (opt_using_transactions)
   {
-    bool operation_done= 0;
+    bool operation_done= 0, need_start_waiters= 0;
     bool transaction_commited= 0;
-
-    /* Update the binary log if we have cached some queries */
-    if (trans == &thd->transaction.all && mysql_bin_log.is_open() &&
+    /* If transaction has done some updates to tables */
+    if (trans == &thd->transaction.all &&
 	my_b_tell(&thd->transaction.trans_log))
     {
-      mysql_bin_log.write(thd, &thd->transaction.trans_log, 1);
-      reinit_io_cache(&thd->transaction.trans_log,
-		      WRITE_CACHE, (my_off_t) 0, 0, 1);
-      thd->transaction.trans_log.end_of_file= max_binlog_cache_size;
+      if (error= wait_if_global_read_lock(thd, 0, 0))
+      {
+        /*
+          Note that ROLLBACK [TO SAVEPOINT] does not have this test; it's
+          because ROLLBACK never updates data, so needn't wait on the lock.
+        */
+        my_error(ER_ERROR_DURING_COMMIT, MYF(0), error);
+        error= 1;
+      }
+      else
+        need_start_waiters= 1;
+      if (mysql_bin_log.is_open())
+      {
+        mysql_bin_log.write(thd, &thd->transaction.trans_log, 1);
+        reinit_io_cache(&thd->transaction.trans_log,
+                        WRITE_CACHE, (my_off_t) 0, 0, 1);
+        thd->transaction.trans_log.end_of_file= max_binlog_cache_size;
+      }
     }
 #ifdef HAVE_BERKELEY_DB
     if (trans->bdb_tid)
@@ -393,6 +406,8 @@ int ha_commit_trans(THD *thd, THD_TRANS* trans)
       statistic_increment(ha_commit_count,&LOCK_status);
       thd->transaction.cleanup();
     }
+    if (need_start_waiters)
+      start_waiting_global_read_lock(thd);
   }
 #endif // using transactions
   DBUG_RETURN(error);