Bug#12809202 61854: MYSQLDUMP --SINGLE-TRANSACTION

             --FLUSH-LOG BREAKS CONSISTENCY

The transaction started by mysqldump gets committed
implicitly when flush-log is specified along with
single-transaction option, and hence can break
consistency.

This is because, COM_REFRESH is executed in order
to flush logs and starting from 5.5 this command
performs an implicit commit.

Fixed by making sure that COM_REFRESH is executed
before the transaction has started and not after it.

Note : This patch triggers following behavioral
       changes in mysqldump :

1) After this patch we no longer flush logs before
   dumping each database if --single-transaction
   option is given like it was done before (in the
   absence of --lock-all-tables and --master-data
   options).

2) Also, after this patch, we start acquiring
   FTWRL before flushing logs in cases when only
   --single-transaction and --flush-logs are given.
   It becomes safe to use mysqldump with these two
   options and without --master-data parameter for
   backups.

1 files changed, 32 insertions, 10 deletions

diff --git a/client/mysqldump.c b/client/mysqldump.c
index 8ccf1f90c97..11b76932692 100644
--- a/client/mysqldump.c
+++ b/client/mysqldump.c
@@ -4079,6 +4079,8 @@ static int dump_all_tables_in_db(char *database)
     if (mysql_refresh(mysql, REFRESH_LOG))
       DB_error(mysql, "when doing refresh");
            /* We shall continue here, if --force was given */
+    else
+      verbose_msg("-- dump_all_tables_in_db : logs flushed successfully!\n");
   }
   while ((table= getTableName(0)))
   {
@@ -4179,6 +4181,8 @@ static my_bool dump_all_views_in_db(char *database)
     if (mysql_refresh(mysql, REFRESH_LOG))
       DB_error(mysql, "when doing refresh");
            /* We shall continue here, if --force was given */
+    else
+      verbose_msg("-- dump_all_views_in_db : logs flushed successfully!\n");
   }
   while ((table= getTableName(0)))
   {
@@ -4317,6 +4321,8 @@ static int dump_selected_tables(char *db, char **table_names, int tables)
       DB_error(mysql, "when doing refresh");
     }
      /* We shall countinue here, if --force was given */
+    else
+      verbose_msg("-- dump_selected_tables : logs flushed successfully!\n");
   }
   if (opt_xml)
     print_xml_tag(md_result_file, "", "\n", "database", "name=", db, NullS);
@@ -4600,6 +4606,7 @@ static int purge_bin_logs_to(MYSQL *mysql_con, char* log_name)
 
 static int start_transaction(MYSQL *mysql_con)
 {
+  verbose_msg("-- Starting transaction...\n");
   /*
     We use BEGIN for old servers. --single-transaction --master-data will fail
     on old servers, but that's ok as it was already silently broken (it didn't
@@ -5199,24 +5206,39 @@ int main(int argc, char **argv)
   if (opt_slave_data && do_stop_slave_sql(mysql))
     goto err;
 
-  if ((opt_lock_all_tables || opt_master_data) &&
+  if ((opt_lock_all_tables || opt_master_data ||
+       (opt_single_transaction && flush_logs)) &&
       do_flush_tables_read_lock(mysql))
     goto err;
-  if (opt_single_transaction && start_transaction(mysql))
-      goto err;
-  if (opt_delete_master_logs)
+
+  /*
+    Flush logs before starting transaction since
+    this causes implicit commit starting mysql-5.5.
+  */
+  if (opt_lock_all_tables || opt_master_data ||
+      (opt_single_transaction && flush_logs) ||
+      opt_delete_master_logs)
   {
-    if (mysql_refresh(mysql, REFRESH_LOG) ||
-        get_bin_log_name(mysql, bin_log_name, sizeof(bin_log_name)))
-      goto err;
+    if (flush_logs || opt_delete_master_logs)
+    {
+      if (mysql_refresh(mysql, REFRESH_LOG))
+        goto err;
+      verbose_msg("-- main : logs flushed successfully!\n");
+    }
+
+    /* Not anymore! That would not be sensible. */
     flush_logs= 0;
   }
-  if (opt_lock_all_tables || opt_master_data)
+
+  if (opt_delete_master_logs)
   {
-    if (flush_logs && mysql_refresh(mysql, REFRESH_LOG))
+    if (get_bin_log_name(mysql, bin_log_name, sizeof(bin_log_name)))
       goto err;
-    flush_logs= 0; /* not anymore; that would not be sensible */
   }
+
+  if (opt_single_transaction && start_transaction(mysql))
+    goto err;
+
   /* Add 'STOP SLAVE to beginning of dump */
   if (opt_slave_apply && add_stop_slave())
     goto err;