MWL#136: Cross-engine consistency for START TRANSACTION WITH CONSISTENT SNAPSHOT

Make the binlog handlerton participate in START TRANSACTION WITH CONSISTENT
SNAPSHOT, recording the binlog position corresponding to the snapshot taken
in other MVCC storage engines.

Expose this consistent binlog position as the new status variables
binlog_trx_file and binlog_trx_position. This enables to get a fully
non-locking snapshot of the database (including binlog position for
slave provisioning), avoiding the need for FLUSH TABLES WITH READ LOCK.

Modify mysqldump to detect if the server supports this new feature, and
if so, avoid FLUSH TABLES WITH READ LOCK for --single-transaction
--master-data snapshot backups.

1 files changed, 95 insertions, 24 deletions

diff --git a/client/mysqldump.c b/client/mysqldump.c
index bb09af4a3c2..bc7f495eb98 100644
--- a/client/mysqldump.c
+++ b/client/mysqldump.c
@@ -77,6 +77,9 @@
 #define IGNORE_DATA 0x01 /* don't dump data for this table */
 #define IGNORE_INSERT_DELAYED 0x02 /* table doesn't support INSERT DELAYED */
 
+/* Chars needed to store LONGLONG, excluding trailing '\0'. */
+#define LONGLONG_LEN 20
+
 static void add_load_option(DYNAMIC_STRING *str, const char *option,
                              const char *option_value);
 static ulong find_set(TYPELIB *lib, const char *x, uint length,
@@ -344,9 +347,9 @@ static struct my_option my_long_options[] =
    "This causes the binary log position and filename to be appended to the "
    "output. If equal to 1, will print it as a CHANGE MASTER command; if equal"
    " to 2, that command will be prefixed with a comment symbol. "
-   "This option will turn --lock-all-tables on, unless "
-   "--single-transaction is specified too (in which case a "
-   "global read lock is only taken a short time at the beginning of the dump; "
+   "This option will turn --lock-all-tables on, unless --single-transaction "
+   "is specified too (on servers before MariaDB 5.3 this will still take a "
+   "global read lock for a short time at the beginning of the dump; "
    "don't forget to read about --single-transaction below). In all cases, "
    "any action on logs will happen at the exact moment of the dump. "
    "Option automatically turns --lock-tables off.",
@@ -1109,6 +1112,44 @@ static int fetch_db_collation(const char *db_name,
 }
 
 
+/*
+  Check if server supports non-blocking binlog position using the
+  binlog_trx_file and binlog_trx_position status variables. If it does,
+  also return the position obtained if output pointers are non-NULL.
+  Returns 1 if position available, 0 if not.
+*/
+static int
+check_consistent_binlog_pos(char *binlog_pos_file, char *binlog_pos_offset)
+{
+  MYSQL_RES *res;
+  MYSQL_ROW row;
+  int found;
+
+  if (mysql_query_with_error_report(mysql, &res,
+                                    "SHOW STATUS LIKE 'binlog_trx_%'"))
+    return 1;
+
+  found= 0;
+  while ((row= mysql_fetch_row(res)))
+  {
+    if (0 == strcmp(row[0], "binlog_trx_file"))
+    {
+      if (binlog_pos_file)
+        strmake(binlog_pos_file, row[1], FN_REFLEN-1);
+      found++;
+    }
+    else if (0 == strcmp(row[0], "binlog_trx_position"))
+    {
+      if (binlog_pos_offset)
+        strmake(binlog_pos_offset, row[1], LONGLONG_LEN);
+      found++;
+    }
+  }
+  mysql_free_result(res);
+
+  return (found == 2);
+}
+
 static char *my_case_str(const char *str,
                          uint str_len,
                          const char *token,
@@ -4351,42 +4392,65 @@ static int dump_selected_tables(char *db, char **table_names, int tables)
 } /* dump_selected_tables */
 
 
-static int do_show_master_status(MYSQL *mysql_con)
+static int do_show_master_status(MYSQL *mysql_con, int consistent_binlog_pos)
 {
   MYSQL_ROW row;
   MYSQL_RES *master;
+  char binlog_pos_file[FN_REFLEN];
+  char binlog_pos_offset[LONGLONG_LEN+1];
+  char *file, *offset;
   const char *comment_prefix=
     (opt_master_data == MYSQL_OPT_MASTER_DATA_COMMENTED_SQL) ? "-- " : "";
-  if (mysql_query_with_error_report(mysql_con, &master, "SHOW MASTER STATUS"))
+
+  if (consistent_binlog_pos)
   {
-    return 1;
+    if(!check_consistent_binlog_pos(binlog_pos_file, binlog_pos_offset))
+      return 1;
+    file= binlog_pos_file;
+    offset= binlog_pos_offset;
   }
   else
   {
+    if (mysql_query_with_error_report(mysql_con, &master, "SHOW MASTER STATUS"))
+      return 1;
+
     row= mysql_fetch_row(master);
     if (row && row[0] && row[1])
     {
-      /* SHOW MASTER STATUS reports file and position */
-      if (opt_comments)
-        fprintf(md_result_file,
-                "\n--\n-- Position to start replication or point-in-time "
-                "recovery from\n--\n\n");
-      fprintf(md_result_file,
-              "%sCHANGE MASTER TO MASTER_LOG_FILE='%s', MASTER_LOG_POS=%s;\n",
-              comment_prefix, row[0], row[1]);
-      check_io(md_result_file);
+      file= row[0];
+      offset= row[1];
     }
-    else if (!ignore_errors)
+    else
     {
-      /* SHOW MASTER STATUS reports nothing and --force is not enabled */
-      my_printf_error(0, "Error: Binlogging on server not active",
-                      MYF(0));
       mysql_free_result(master);
-      maybe_exit(EX_MYSQLERR);
-      return 1;
+      if (!ignore_errors)
+      {
+        /* SHOW MASTER STATUS reports nothing and --force is not enabled */
+        my_printf_error(0, "Error: Binlogging on server not active",
+                        MYF(0));
+        maybe_exit(EX_MYSQLERR);
+        return 1;
+      }
+      else
+      {
+        return 0;
+      }
     }
-    mysql_free_result(master);
   }
+
+  /* SHOW MASTER STATUS reports file and position */
+  if (opt_comments)
+    fprintf(md_result_file,
+            "\n--\n-- Position to start replication or point-in-time "
+            "recovery from\n--\n\n");
+  fprintf(md_result_file,
+          "%sCHANGE MASTER TO MASTER_LOG_FILE='%s', MASTER_LOG_POS=%s;\n",
+          comment_prefix, file, offset);
+  check_io(md_result_file);
+
+  if (!consistent_binlog_pos)
+    mysql_free_result(master);
+
   return 0;
 }
 
@@ -5025,6 +5089,7 @@ int main(int argc, char **argv)
 {
   char bin_log_name[FN_REFLEN];
   int exit_code;
+  int consistent_binlog_pos= 0;
   MY_INIT("mysqldump");
 
   compatible_mode_normal_str[0]= 0;
@@ -5055,7 +5120,13 @@ int main(int argc, char **argv)
   if (!path)
     write_header(md_result_file, *argv);
 
-  if ((opt_lock_all_tables || opt_master_data) &&
+  if (opt_single_transaction && opt_master_data)
+  {
+    /* See if we can avoid FLUSH TABLES WITH READ LOCK (MariaDB 5.3+). */
+    consistent_binlog_pos= check_consistent_binlog_pos(NULL, NULL);
+  }
+
+  if ((opt_lock_all_tables || (opt_master_data && !consistent_binlog_pos)) &&
       do_flush_tables_read_lock(mysql))
     goto err;
   if (opt_single_transaction && start_transaction(mysql))
@@ -5073,7 +5144,7 @@ int main(int argc, char **argv)
       goto err;
     flush_logs= 0; /* not anymore; that would not be sensible */
   }
-  if (opt_master_data && do_show_master_status(mysql))
+  if (opt_master_data && do_show_master_status(mysql, consistent_binlog_pos))
     goto err;
   if (opt_single_transaction && do_unlock_tables(mysql)) /* unlock but no commit! */
     goto err;