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, 8 insertions, 0 deletions

diff --git a/sql/wsrep_dummy.cc b/sql/wsrep_dummy.cc
index 5837ab4bed5..795e2d19252 100644
--- a/sql/wsrep_dummy.cc
+++ b/sql/wsrep_dummy.cc
@@ -125,6 +125,14 @@ longlong wsrep_thd_trx_seqno(THD *)
 struct wsrep_ws_handle* wsrep_thd_ws_handle(THD *)
 { return 0; }
 
+void wsrep_thd_auto_increment_variables(THD *thd,
+                                        unsigned long long *offset,
+                                        unsigned long long *increment)
+{
+  *offset= thd->variables.auto_increment_offset;
+  *increment= thd->variables.auto_increment_increment;
+}
+
 int wsrep_trx_is_aborting(THD *)
 { return 0; }