Bug#35784192 tablespace is missing for table innodb_undo_002

This bug reports following two problems:

Querying the information schema reports undo tablespace is missing -
  while an undo file is present.
Purge threads don't remove the undo_space_number_trunc.log file.

While the first problem is already fixed through Bug#32104924, Bug#32654667

This bug fix aims to address the second problem.

The purge thread attempts to lock dictionary tables, while truncating
the undo tablespace. This lock can't be acquired in
a read-only MySQL instance, except when the thread has some special
flags associated with it. In this case, we use the skip_readonly_check
member of the thread descriptor struct, to signal that the readonly
check should not be applied to the purge thread. This is done
via the set_skip_readonly_check() method.

Change-Id: Iea6255ff6654752db8658bdd422cc3e58e3a8a97

Author: GBuella

mysql-test/suite/innodb_undo/r/purge_on_replica.result

@@ -0,0 +1,49 @@
+include/master-slave.inc
+Warnings:
+Note	####	Sending passwords in plain text without SSL/TLS is extremely insecure.
+Note	####	Storing MySQL user name or password information in the connection metadata repository is not secure and is therefore not recommended. Please consider using the USER and PASSWORD connection options for START REPLICA; see the 'START REPLICA Syntax' in the MySQL Manual for more information.
+[connection master]
+# 1: Set replica parameters
+set @orig_max_undo_log_size = @@innodb_max_undo_log_size;
+set @orig_truncate_frequency = @@innodb_purge_rseg_truncate_frequency;
+set global innodb_max_undo_log_size=10485760;
+set global innodb_purge_rseg_truncate_frequency=1;
+set global super_read_only=1;
+
+# 2: Preparing database
+create table t1(id int);
+create procedure insert_data()
+begin
+declare i int;
+set i=1;
+while(i<=500000) do
+insert into t1(id) values(i);
+set i=i+1;
+end while;
+end;$$
+begin;
+# 3: Inserting data, filling undo logs
+call insert_data();
+# 4: commit, trigger undo log truncation
+commit;
+select tablespace_name, file_name from information_schema.files
+where file_name like "%undo%";
+TABLESPACE_NAME	FILE_NAME
+innodb_undo_001	./undo_001
+innodb_undo_002	./undo_002
+select name, row_format, server_version from information_schema.innodb_tablespaces
+where name like '%undo%';
+name	row_format	server_version
+innodb_undo_001	Undo	8.4.0
+innodb_undo_002	Undo	8.4.0
+# 5: undo files undo_001 and undo_002 are expected to exist,
+#    while files undo_001_trunc.log and undo_002_trunc.log are expected to not exist
+undo_001
+undo_002
+set global innodb_max_undo_log_size=@orig_max_undo_log_size;
+set global innodb_purge_rseg_truncate_frequency=@orig_truncate_frequency;
+set global super_read_only = 0;
+set global read_only = 0;
+drop procedure insert_data;
+drop table t1;
+include/rpl_end.inc

mysql-test/suite/innodb_undo/t/purge_on_replica.test

@@ -0,0 +1,71 @@
+--source include/have_debug.inc
+# The test requires a debug build, in order to trigger
+# a purge using innodb_purge_run_now=ON .
+
+--source include/master-slave.inc
+
+--echo # 1: Set replica parameters
+connection slave;
+
+set @orig_max_undo_log_size = @@innodb_max_undo_log_size;
+set @orig_truncate_frequency = @@innodb_purge_rseg_truncate_frequency;
+
+# Trigger truncation of undo log files once they occupy more than 10MB
+# which is the minimum value of innodb_max_undo_log_size
+set global innodb_max_undo_log_size=10485760;
+set global innodb_purge_rseg_truncate_frequency=1;
+set global super_read_only=1;
+
+--echo
+--echo # 2: Preparing database
+connection master;
+
+create table t1(id int);
+
+delimiter $$;
+create procedure insert_data()
+begin
+ declare i int;
+ set i=1;
+ while(i<=500000) do
+    insert into t1(id) values(i);
+    set i=i+1;
+ end while;
+end;$$
+delimiter ;$$
+
+begin;
+
+--echo # 3: Inserting data, filling undo logs
+call insert_data();
+
+--echo # 4: commit, trigger undo log truncation
+commit;
+sync_slave_with_master;
+
+connection slave;
+
+--source include/wait_innodb_all_purged.inc
+
+
+# expecting two undo files, and no undo_*_trunc.log files remaining
+
+select tablespace_name, file_name from information_schema.files
+  where file_name like "%undo%";
+select name, row_format, server_version from information_schema.innodb_tablespaces
+  where name like '%undo%';
+
+let $MYSQLD_DATADIR = `select @@datadir`;
+
+--echo # 5: undo files undo_001 and undo_002 are expected to exist,
+--echo #    while files undo_001_trunc.log and undo_002_trunc.log are expected to not exist
+list_files $MYSQLD_DATADIR undo_0*;
+
+set global innodb_max_undo_log_size=@orig_max_undo_log_size;
+set global innodb_purge_rseg_truncate_frequency=@orig_truncate_frequency;
+set global super_read_only = 0;
+set global read_only = 0;
+connection master;
+drop procedure insert_data;
+drop table t1;
+--source include/rpl_end.inc

storage/innobase/srv/srv0srv.cc

@@ -78,6 +78,7 @@ this program; if not, write to the Free Software Foundation, Inc.,
 #include "pars0pars.h"
 #include "que0que.h"
 #include "row0mysql.h"
+#include "sql/sql_class.h"
 #include "sql_thd_internal_api.h"
 #include "srv0mon.h"
 
@@ -3084,6 +3085,9 @@ void srv_purge_coordinator_thread() {
 
   THD *thd = create_internal_thd();
 
+  // Allow purge in read only mode as well.
+  thd->set_skip_readonly_check();
+
   purge_sys->is_this_a_purge_thread = true;
 
   ulint n_total_purged = ULINT_UNDEFINED;