MDEV-18863: Galera SST scripts can't read [mysqldN] option groups

Some users and some scripts (for example, mysqld_multi.sh) use special
option groups with names like [mysqld1], [mysqld2], ..., [mysqldN].

But SST scripts can't currently fully support these option groups.
The only option group-related value it gets from the server is
--defaults-group-suffix, if that option was set for mysqld when
the server was started.

However, the SST scripts does not get told by the server to read
these option groups, so this means that the SST script will fail
to read options like innodb-data-home-dir when it is in a option
group like [mysqld1]...[mysqldN].

Moreover, SST scripts ignore many parameters that can be passed
to them explicitly and cannot transfer them further, for example,
to the input of mariabackup utility. Ideally, we want to transfer
all the parameters of the original mysqld call to utilities such
as mariabackup, however the SST script does not receive these
parameters from the server and therefore cannot transfer them to
mariabackup.

To correct these shortcomings, we need to transfer to the scripts
all of the parameters of the original mysqld call, and in the SST
scripts themselves provide for the transfer all of these parameters
to utilities such as mariabackup. To prevent these parameters from
mixing with the script's own parameters, they should be transferred
to SST script after the special option "--mysqld-args", followed by
the string argument with the original parameters, as it received by
the mysqld call at the time of launch (further all these parameters
will be passed to mariabackup, for example).

In addition, the SST scripts themselves must be refined so that
they can read the parameters from the user-selected group, not just
from the global mysqld configuration group. And also so that they
can receive the parameters (which important for their work) as
command-line arguments.

1 files changed, 1 insertions, 0 deletions

diff --git a/sql/wsrep_sst.h b/sql/wsrep_sst.h
index eb218647bc0..2389db4abe7 100644
--- a/sql/wsrep_sst.h
+++ b/sql/wsrep_sst.h
@@ -32,6 +32,7 @@
 #define WSREP_SST_OPT_PARENT   "--parent"
 #define WSREP_SST_OPT_BINLOG   "--binlog"
 #define WSREP_SST_OPT_BINLOG_INDEX "--binlog-index"
+#define WSREP_SST_OPT_MYSQLD   "--mysqld-args"
 
 // mysqldump-specific options
 #define WSREP_SST_OPT_USER     "--user"