MDEV-14648 Restore fix for MySQL BUG#39053 - UNINSTALL PLUGIN does not allow the storage engine to cleanup open connections

Also, allow the MariaDB 10.2 server to link InnoDB dynamically
against ha_innodb.so (which is what mysql-test-run.pl expects
to exist, instead of the default name ha_innobase.so).

wsrep_load_data_split(): Instead of referring to innodb_hton_ptr,
check the handlerton::db_type. This was recently broken by me in
MDEV-11415.

innodb_lock_schedule_algorithm: Define as a weak global symbol,
so that WITH_WSREP will not depend on InnoDB being linked statically.
I tested this manually. Notably, running a test that only does
	SET GLOBAL wsrep_on=1;
with a static or dynamic InnoDB and
	./mtr --mysqld=--loose-innodb-lock-schedule-algorithm=fcfs
will crash with SIGSEGV at shutdown. With the default VATS
combination the wsrep_on is properly refused for both the
static and dynamic InnoDB.

ha_close_connection(): Do invoke the method also for plugins
for which UNINSTALL PLUGIN was deferred due to open connections.
Thanks to @svoj for pointing this out.

thd_to_trx(): Return a pointer, not a reference to a pointer.

check_trx_exists(): Invoke thd_set_ha_data() for assigning a transaction.

log_write_checkpoint_info(): Remove an unused DEBUG_SYNC point
that would cause an assertion failure on shutdown after deferred
UNINSTALL PLUGIN.

This was tested as follows:

cmake -DWITH_WSREP=1 -DPLUGIN_INNOBASE:STRING=DYNAMIC \
-DWITH_MARIABACKUP:BOOL=OFF ...
make
cd mysql-test
./mtr innodb.innodb_uninstall

1 files changed, 12 insertions, 10 deletions

diff --git a/sql/sql_load.cc b/sql/sql_load.cc
index e15d4d2fec5..70a6787d63b 100644
--- a/sql/sql_load.cc
+++ b/sql/sql_load.cc
@@ -104,23 +104,25 @@ the transaction after every 10,000 inserted rows. */
 static bool wsrep_load_data_split(THD *thd, const TABLE *table,
 				  const COPY_INFO &info)
 {
-  extern struct handlerton* innodb_hton_ptr;
-
   DBUG_ENTER("wsrep_load_data_split");
 
-  if (wsrep_load_data_splitting && wsrep_on(thd)
-      && info.records && !(info.records % 10000)
-      && thd->transaction.stmt.ha_list
-      && thd->transaction.stmt.ha_list->ht() == binlog_hton
-      && thd->transaction.stmt.ha_list->next()
-      && thd->transaction.stmt.ha_list->next()->ht() == innodb_hton_ptr
-      && !thd->transaction.stmt.ha_list->next()->next())
+  if (!wsrep_load_data_splitting || !wsrep_on(thd)
+      || !info.records || (info.records % 10000)
+      || !thd->transaction.stmt.ha_list
+      || thd->transaction.stmt.ha_list->ht() != binlog_hton
+      || !thd->transaction.stmt.ha_list->next()
+      || thd->transaction.stmt.ha_list->next()->next())
+    DBUG_RETURN(false);
+
+  if (handlerton* hton= thd->transaction.stmt.ha_list->next()->ht())
   {
+    if (hton->db_type != DB_TYPE_INNODB)
+      DBUG_RETURN(false);
     WSREP_DEBUG("intermediate transaction commit in LOAD DATA");
     if (wsrep_run_wsrep_commit(thd, true) != WSREP_TRX_OK) DBUG_RETURN(true);
     if (binlog_hton->commit(binlog_hton, thd, true)) DBUG_RETURN(true);
     wsrep_post_commit(thd, true);
-    innodb_hton_ptr->commit(innodb_hton_ptr, thd, true);
+    hton->commit(hton, thd, true);
     table->file->extra(HA_EXTRA_FAKE_START_STMT);
   }