MDEV-9519: Data corruption will happen on the Galera cluster size change

If we have a 2+ node cluster which is replicating from an async master
and the binlog_format is set to STATEMENT and multi-row inserts are executed
on a table with an auto_increment column such that values are automatically
generated by MySQL, then the server node generates wrong auto_increment
values, which are different from what was generated on the async master.

In the title of the MDEV-9519 it was proposed to ban start slave on a Galera
if master binlog_format = statement and wsrep_auto_increment_control = 1,
but the problem can be solved without such a restriction.

The causes and fixes:

1. We need to improve processing of changing the auto-increment values
after changing the cluster size.

2. If wsrep auto_increment_control switched on during operation of
the node, then we should immediately update the auto_increment_increment
and auto_increment_offset global variables, without waiting of the next
invocation of the wsrep_view_handler_cb() callback. In the current version
these variables retain its initial values if wsrep_auto_increment_control
is switched on during operation of the node, which leads to inconsistent
results on the different nodes in some scenarios.

3. If wsrep auto_increment_control switched off during operation of the node,
then we must return the original values of the auto_increment_increment and
auto_increment_offset global variables, as the user has set. To make this
possible, we need to add a "shadow copies" of these variables (which stores
the latest values set by the user).

https://jira.mariadb.org/browse/MDEV-9519

1 files changed, 92 insertions, 1 deletions

diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index 9bb7436b2da..2a793646c7f 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -347,13 +347,56 @@ static Sys_var_long Sys_pfs_connect_attrs_size(
 
 #endif /* WITH_PERFSCHEMA_STORAGE_ENGINE */
 
+#ifdef WITH_WSREP
+
+/*
+  We need to keep the original values set by the user, as they will
+  be lost if wsrep_auto_increment_control set to 'ON':
+*/
+static bool update_auto_increment_increment (sys_var *self, THD *thd, enum_var_type type)
+{
+  if (type == OPT_GLOBAL)
+    global_system_variables.saved_auto_increment_increment=
+      global_system_variables.auto_increment_increment;
+  else
+    thd->variables.saved_auto_increment_increment=
+      thd->variables.auto_increment_increment;
+  return false;
+}
+
+#endif /* WITH_WSREP */
+
 static Sys_var_ulong Sys_auto_increment_increment(
        "auto_increment_increment",
        "Auto-increment columns are incremented by this",
        SESSION_VAR(auto_increment_increment),
        CMD_LINE(OPT_ARG),
        VALID_RANGE(1, 65535), DEFAULT(1), BLOCK_SIZE(1),
+#ifdef WITH_WSREP
+       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
+       ON_UPDATE(update_auto_increment_increment));
+#else
        NO_MUTEX_GUARD, IN_BINLOG);
+#endif /* WITH_WSREP */
+
+#ifdef WITH_WSREP
+
+/*
+  We need to keep the original values set by the user, as they will
+  be lost if wsrep_auto_increment_control set to 'ON':
+*/
+static bool update_auto_increment_offset (sys_var *self, THD *thd, enum_var_type type)
+{
+  if (type == OPT_GLOBAL)
+    global_system_variables.saved_auto_increment_offset=
+      global_system_variables.auto_increment_offset;
+  else
+    thd->variables.saved_auto_increment_offset=
+      thd->variables.auto_increment_offset;
+  return false;
+}
+
+#endif /* WITH_WSREP */
 
 static Sys_var_ulong Sys_auto_increment_offset(
        "auto_increment_offset",
@@ -362,7 +405,12 @@ static Sys_var_ulong Sys_auto_increment_offset(
        SESSION_VAR(auto_increment_offset),
        CMD_LINE(OPT_ARG),
        VALID_RANGE(1, 65535), DEFAULT(1), BLOCK_SIZE(1),
+#ifdef WITH_WSREP
+       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
+       ON_UPDATE(update_auto_increment_offset));
+#else
        NO_MUTEX_GUARD, IN_BINLOG);
+#endif /* WITH_WSREP */
 
 static Sys_var_mybool Sys_automatic_sp_privileges(
        "automatic_sp_privileges",
@@ -4980,11 +5028,54 @@ static Sys_var_ulong Sys_wsrep_retry_autocommit(
        SESSION_VAR(wsrep_retry_autocommit), CMD_LINE(REQUIRED_ARG),
        VALID_RANGE(0, 10000), DEFAULT(1), BLOCK_SIZE(1));
 
+static bool update_wsrep_auto_increment_control (sys_var *self, THD *thd, enum_var_type type)
+{
+  if (wsrep_auto_increment_control)
+  {
+    /*
+      The variables that control auto increment shall be calculated
+      automaticaly based on the size of the cluster. This usually done
+      within the wsrep_view_handler_cb callback. However, if the user
+      manually sets the value of wsrep_auto_increment_control to 'ON',
+      then we should to re-calculate these variables again (because
+      these values may be required before wsrep_view_handler_cb will
+      be re-invoked, which is rarely invoked if the cluster stays in
+      the stable state):
+    */
+    global_system_variables.auto_increment_increment=
+       wsrep_cluster_size ? wsrep_cluster_size : 1;
+    global_system_variables.auto_increment_offset=
+       wsrep_local_index >= 0 ? wsrep_local_index + 1 : 1;
+    thd->variables.auto_increment_increment=
+      global_system_variables.auto_increment_increment;
+    thd->variables.auto_increment_offset=
+      global_system_variables.auto_increment_offset;
+  }
+  else
+  {
+    /*
+      We must restore the last values of the variables that
+      are explicitly specified by the user:
+    */
+    global_system_variables.auto_increment_increment=
+      global_system_variables.saved_auto_increment_increment;
+    global_system_variables.auto_increment_offset=
+      global_system_variables.saved_auto_increment_offset;
+    thd->variables.auto_increment_increment=
+      thd->variables.saved_auto_increment_increment;
+    thd->variables.auto_increment_offset=
+      thd->variables.saved_auto_increment_offset;
+  }
+  return false;
+}
+
 static Sys_var_mybool Sys_wsrep_auto_increment_control(
        "wsrep_auto_increment_control", "To automatically control the "
        "assignment of autoincrement variables",
        GLOBAL_VAR(wsrep_auto_increment_control), 
-       CMD_LINE(OPT_ARG), DEFAULT(TRUE));
+       CMD_LINE(OPT_ARG), DEFAULT(TRUE),
+       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
+       ON_UPDATE(update_wsrep_auto_increment_control));
 
 static Sys_var_mybool Sys_wsrep_drupal_282555_workaround(
        "wsrep_drupal_282555_workaround", "Enable a workaround to handle the "