Addendum:
* Before calling THD::init_for_queries(), flip the current_thd to wsrep
thread so that memory gets allocated for the right THD.
* Use wsrep_creating_startup_threads instead of plugins_are_initialized
as the condition for the execution of THD::init_for_queries() within
start_wsrep_THD(), as use of latter could still leave some room for
race.
Problem:
When mysqld starts as a galera node, it creates 2 system threads
(applier & rollbacker) using start_wsrep_THD(). These threads are
created before plugin initialization (plugin_init()) for SST methods
like rsync and xtrabackup.
The threads' initialization itself can proceed in parallel to mysqld's
main thread of execution. As a result, the thread initialization code
(start_wsrep_THD()) can end up accessing some un/partially initialized
structures (like maria_hton, in this particular case) resulting in
segfault.
Solution:
Fixed by calling THD::init_for_queries() (which accesses maria_hton)
only after the plugins have been initialized.
Before this, FLUSH TABLES and FLUSH TABLES t1 (REFRESH_TABLES hereafter) were executed locally,
which also had implications for GTID. MySQL async replication does
replicate FLUSH TABLES.
Hence, this commit
a) Adds REFRESH_TABLES to TOI.
b) Skips LOCK-based REFRESH_TABLES from TOI, ie. FLUSH TABLES WITH READ
LOCK and FLUSH TABLES FOR EXPORT.
c) Executes them after reload_acl_and_cache. This is done since
reload_acl_and_cache checks for thd->locked_tables_mode and does upgrade
of MDL locks accordingly. A failure here means REFRESH_TABLES cannot
run.
i) This is also important since LOCK TABLES is not replicated in
galera.
d) Test galera_flush has been modified for
i) wsrep_replicate_myisam SESSION variable.
ii) Testing REFRESH_TABLES.
iii) Testing REFRESH_TABLES + LOCK TABLES.
e) Use different WSREP_TO_ISOLATION_BEGIN for global FLUSH TABLES and FLUSH TABLES <table,>.
- errno handling in wsp::env::append() method, where error could be returned by mistake
- return code of sst_prepare_other() when pthread_create() fails - it was returning positive error code which by convention is treated as success.
1. Passes wsrep_sst_auth_value to SST scripts via WSREP_SST_OPT_AUTH envronmental variable, so it never appears on the command line
2. In mysqldump and xtrabackup* SST scripts which rely on MySQL authentication, instead of passing password on the command line, SST script sets MYSQL_PWD environment variable, so that password also never appears on the mysqldump/innobackupex command line.
