MDEV-15826 Purge attempts to free BLOB page after BEGIN;INSERT;UPDATE;ROLLBACK

- During rollback, redo segments priorities over no-redo rollback
segments and it leads to failure of redo rollback segment undo
logs truncation.

mysql-test/suite/innodb/r/undo_log.result

@@ -140,3 +140,16 @@ CHECK TABLE test_tab;
 Table	Op	Msg_type	Msg_text
 test.test_tab	check	status	OK
 DROP TABLE test_tab;
+SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
+SET GLOBAL innodb_purge_rseg_truncate_frequency = 1;
+CREATE TEMPORARY TABLE t2(i INT)ENGINE=InnoDB;
+CREATE TABLE t1(i TEXT NOT NULL) ENGINE=INNODB;
+BEGIN;
+INSERT t1 SET i=REPEAT('1234567890',840);
+UPDATE t1 SET i='';
+INSERT INTO t2 VALUES(2);
+ROLLBACK;
+InnoDB		0 transactions not purged
+DROP TABLE t1;
+DROP TABLE t2;
+SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;

mysql-test/suite/innodb/t/undo_log.test

@@ -137,3 +137,17 @@ ROLLBACK;
 SELECT COUNT(*) FROM test_tab;
 CHECK TABLE test_tab;
 DROP TABLE test_tab;
+
+SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
+SET GLOBAL innodb_purge_rseg_truncate_frequency = 1;
+CREATE TEMPORARY TABLE t2(i INT)ENGINE=InnoDB;
+CREATE TABLE t1(i TEXT NOT NULL) ENGINE=INNODB;
+BEGIN;
+INSERT t1 SET i=REPEAT('1234567890',840);
+UPDATE t1 SET i='';
+INSERT INTO t2 VALUES(2);
+ROLLBACK;
+--source include/wait_all_purged.inc
+DROP TABLE t1;
+DROP TABLE t2;
+SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;

storage/innobase/trx/trx0roll.cc

@@ -1003,7 +1003,7 @@ trx_roll_pop_top_rec_of_trx(trx_t* trx, roll_ptr_t* roll_ptr, mem_heap_t* heap)
 		trx_roll_try_truncate(trx);
 	}
 
-	trx_undo_t*	undo;
+	trx_undo_t*	undo = NULL;
 	trx_undo_t*	insert	= trx->rsegs.m_redo.insert_undo;
 	trx_undo_t*	update	= trx->rsegs.m_redo.update_undo;
 	trx_undo_t*	temp	= trx->rsegs.m_noredo.undo;
@@ -1017,17 +1017,26 @@ trx_roll_pop_top_rec_of_trx(trx_t* trx, roll_ptr_t* roll_ptr, mem_heap_t* heap)
 	      || update->top_undo_no != temp->top_undo_no);
 
 	if (insert && !insert->empty && limit <= insert->top_undo_no) {
-		if (update && !update->empty
-		    && update->top_undo_no > insert->top_undo_no) {
+		undo = insert;
+	}
+
+	if (update && !update->empty && update->top_undo_no >= limit) {
+		if (!undo) {
+			undo = update;
+		} else if (undo->top_undo_no < update->top_undo_no) {
 			undo = update;
-		} else {
-			undo = insert;
 		}
-	} else if (update && !update->empty && limit <= update->top_undo_no) {
-		undo = update;
-	} else if (temp && !temp->empty && limit <= temp->top_undo_no) {
-		undo = temp;
-	} else {
+	}
+
+	if (temp && !temp->empty && temp->top_undo_no >= limit) {
+		if (!undo) {
+			undo = temp;
+		} else if (undo->top_undo_no < temp->top_undo_no) {
+			undo = temp;
+		}
+	}
+
+	if (undo == NULL) {
 		trx_roll_try_truncate(trx);
 		/* Mark any ROLLBACK TO SAVEPOINT completed, so that
 		if the transaction object is committed and reused