MDEV-14905 Fulltext index modification committed during shutdown

If CREATE TABLE...FULLTEXT INDEX was initiated right before shutdown,
then the function fts_load_stopword() could commit modifications
after shutdown was initiated, causing an assertion failure in
the function trx_purge_add_update_undo_to_history().

Mark as internal all the read/write transactions that
modify fulltext indexes, so that they will be ignored by
the assertion that guards against transaction commits
after shutdown has been initiated.

fts_optimize_free(): Invoke trx_commit_for_mysql() just in case,
because in fts_optimize_create() we started the transaction as
internal, and fts_free_for_backgruond() would assert that the
flag is clear. Transaction commit would clear the flag.

storage/innobase/fts/fts0fts.cc

@@ -2699,6 +2699,7 @@ fts_cmp_set_sync_doc_id(
 	fts_table.parent = table->name.m_name;
 
 	trx = trx_allocate_for_background();
+	trx_start_internal(trx);
 
 	trx->op_info = "update the next FTS document id";
 
@@ -2819,6 +2820,7 @@ fts_update_sync_doc_id(
 
 	if (!trx) {
 		trx = trx_allocate_for_background();
+		trx_start_internal(trx);
 
 		trx->op_info = "setting last FTS document id";
 		local_trx = TRUE;
@@ -3056,6 +3058,8 @@ fts_commit_table(
 	fts_cache_t*		cache = ftt->table->fts->cache;
 	trx_t*			trx = trx_allocate_for_background();
 
+	trx_start_internal(trx);
+
 	rows = ftt->rows;
 
 	ftt->fts_trx->trx = trx;
@@ -3792,6 +3796,7 @@ fts_doc_fetch_by_doc_id(
 	trx_t*		trx = trx_allocate_for_background();
 	que_t*          graph;
 
+	trx_start_internal(trx);
 	trx->op_info = "fetching indexed FTS document";
 
 	/* The FTS index can be supplied by caller directly with
@@ -4138,6 +4143,7 @@ fts_sync_begin(
 	sync->start_time = ut_time();
 
 	sync->trx = trx_allocate_for_background();
+	trx_start_internal(sync->trx);
 
 	if (fts_enable_diag_print) {
 		ib::info() << "FTS SYNC for table " << sync->table->name
@@ -5008,7 +5014,6 @@ fts_get_rows_count(
 	char		table_name[MAX_FULL_NAME_LEN];
 
 	trx = trx_allocate_for_background();
-
 	trx->op_info = "fetching FT table rows count";
 
 	info = pars_info_create();
@@ -7350,6 +7355,7 @@ fts_load_stopword(
 
 	if (!trx) {
 		trx = trx_allocate_for_background();
+		trx_start_internal(trx);
 		trx->op_info = "upload FTS stopword";
 		new_trx = TRUE;
 	}

storage/innobase/fts/fts0opt.cc

 /*****************************************************************************
 
 Copyright (c) 2007, 2017, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2016, MariaDB Corporation. All Rights reserved.
+Copyright (c) 2016, 2018, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -989,6 +989,7 @@ fts_table_fetch_doc_ids(
 
 	if (!trx) {
 		trx = trx_allocate_for_background();
+		trx_start_internal(trx);
 		alloc_bk_trx = TRUE;
 	}
 
@@ -1619,6 +1620,7 @@ fts_optimize_create(
 	optim->table = table;
 
 	optim->trx = trx_allocate_for_background();
+	trx_start_internal(optim->trx);
 
 	optim->fts_common_table.parent = table->name.m_name;
 	optim->fts_common_table.table_id = table->id;
@@ -1741,6 +1743,7 @@ fts_optimize_free(
 {
 	mem_heap_t*	heap = static_cast<mem_heap_t*>(optim->self_heap->arg);
 
+	trx_commit_for_mysql(optim->trx);
 	trx_free_for_background(optim->trx);
 
 	fts_doc_ids_free(optim->to_delete);