MDEV-32050: Deprecate&ignore innodb_purge_rseg_truncate_frequency

The motivation of introducing the parameter
innodb_purge_rseg_truncate_frequency in
mysql/mysql-server@28bbd66ea5 and
mysql/mysql-server@8fc2120fed
seems to have been to avoid stalls due to freeing undo log pages
or truncating undo log tablespaces. In MariaDB Server,
innodb_undo_log_truncate=ON should be a much lighter operation
than in MySQL, because it will not involve any log checkpoint.

Another source of performance stalls should be
trx_purge_truncate_rseg_history(), which is shrinking the history list
by freeing the undo log pages whose undo records have been purged.
To alleviate that, we will introduce a purge_truncation_task that will
offload this from the purge_coordinator_task. In that way, the next
innodb_purge_batch_size pages may be parsed and purged while the pages
from the previous batch are being freed and the history list being shrunk.

The processing of innodb_undo_log_truncate=ON will still remain the
responsibility of the purge_coordinator_task.

purge_coordinator_state::count: Remove. We will ignore
innodb_purge_rseg_truncate_frequency, and act as if it had been
set to 1 (the maximum shrinking frequency).

purge_coordinator_state::do_purge(): Invoke an asynchronous task
purge_truncation_callback() to free the undo log pages.

purge_sys_t::iterator::free_history(): Free those undo log pages
that have been processed. This used to be a part of
trx_purge_truncate_history().

purge_sys_t::clone_end_view(): Take a new value of purge_sys.head
as a parameter, so that it will be updated while holding exclusive
purge_sys.latch. This is needed for race-free access to the field
in purge_truncation_callback().

Reviewed by: Vladislav Lesin

mysql-test/suite/innodb_gis/t/rtree_add_index.test

@@ -1,8 +1,5 @@
 --source include/have_innodb.inc
 
-SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
-SET GLOBAL innodb_purge_rseg_truncate_frequency = 1;
-
 CREATE TABLE t1 (g MULTIPOINT NOT NULL) ENGINE=InnoDB;
 INSERT INTO t1 VALUES ('');
 
@@ -17,4 +14,3 @@ ALTER TABLE t1 ADD SPATIAL INDEX (g);
 disconnect purge_control;
 --source ../../innodb/include/wait_all_purged.inc
 DROP TABLE t1;
-SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;

mysql-test/suite/innodb_gis/t/rtree_compress.test

@@ -10,9 +10,6 @@
 # Valgrind takes too much time on PB2 even in the --big-test runs.
 --source include/not_valgrind.inc
 
-SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
-SET GLOBAL innodb_purge_rseg_truncate_frequency = 1;
-
 create table t1 (c1 int, c2 geometry not null, spatial index (c2))engine=innodb ROW_FORMAT=COMPRESSED;
 
 # Insert enough values to let R-tree split.
@@ -61,4 +58,3 @@ SET debug_dbug = @saved_dbug;
 
 # Clean up.
 drop table t1;
-SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;

mysql-test/suite/innodb_gis/t/rtree_purge.test

@@ -6,9 +6,6 @@
 # This test often times out with MSAN
 --source include/not_msan.inc
 
-SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
-SET GLOBAL innodb_purge_rseg_truncate_frequency = 1;
-
 create table t (
   b point not null,d point not null, spatial key (d),spatial key (b)
 ) engine=innodb;
@@ -29,4 +26,3 @@ dec $n;
 
 # Clean up.
 drop table t;
-SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;

mysql-test/suite/innodb_gis/t/rtree_undo.test

@@ -6,9 +6,6 @@
 --source include/innodb_row_format.inc
 --source include/count_sessions.inc
 
-SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
-SET GLOBAL innodb_purge_rseg_truncate_frequency = 1;
-
 connect (control_purge,localhost,root,,);
 connection default;
 
@@ -100,5 +97,3 @@ dec $index;
 
 disconnect control_purge;
 --source include/wait_until_count_sessions.inc
-
-SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;