MDEV-32050: Do not copy undo records in purge

Also, default to innodb_purge_batch_size=1000,
replacing the old default value of processing 300 undo log pages
in a batch. Axel Schwenke found this value to help reduce purge lag
without having a significant impact on workload throughput.

In purge, we can simply acquire a shared latch on the undo log page
(to avoid a race condition like the one that was fixed in
commit b102872ad5) and retain a buffer-fix
after releasing the latch. The buffer-fix will prevent the undo log
page from being evicted from the buffer pool. Concurrent modification
is prevented by design. Only the purge_coordinator_task
(or its accomplice purge_truncation_task) may free the undo log pages,
after any purge_worker_task have completed execution. Hence, we do not
have to worry about any overwriting or reuse of the undo log records.

trx_undo_rec_copy(): Remove. The only remaining caller would have been
trx_undo_get_undo_rec_low(), which is where the logic was merged.

purge_sys_t::m_initialized: Replaces heap.

purge_sys_t::pages: A cache of buffer-fixed pages that have been
looked up from buf_pool.page_hash.

purge_sys_t::get_page(): Return a buffer-fixed undo page, using the
pages cache.

trx_purge_t::batch_cleanup(): Renamed from clone_end_view().
Clear the pages cache and clone the end_view at the end of a batch.

purge_sys_t::n_pages_handled(): Return pages.size(). This determines
if innodb_purge_batch_size was exceeded.

purge_sys_t::rseg_get_next_history_log(): Replaces
trx_purge_rseg_get_next_history_log().

purge_sys_t::choose_next_log(): Replaces trx_purge_choose_next_log()
and trx_purge_read_undo_rec().

purge_sys_t::get_next_rec(): Replaces trx_purge_get_next_rec()
and trx_undo_get_next_rec().

purge_sys_t::fetch_next_rec(): Replaces trx_purge_fetch_next_rec()
and some use of trx_undo_get_first_rec().

trx_purge_attach_undo_recs(): Do not allow purge_sys.n_pages_handled()
exceed the innodb_purge_batch_size or ¾ of the buffer pool, whichever
is smaller.

Reviewed by: Vladislav Lesin
Tested by: Matthias Leich and Axel Schwenke

mysql-test/suite/sys_vars/r/innodb_purge_batch_size_basic.result

@@ -1,19 +1,19 @@
 SET @global_start_value = @@global.innodb_purge_batch_size;
 SELECT @global_start_value;
 @global_start_value
-300
+1000
 '#--------------------FN_DYNVARS_046_01------------------------#'
 SET @@global.innodb_purge_batch_size = 1;
 SET @@global.innodb_purge_batch_size = DEFAULT;
 SELECT @@global.innodb_purge_batch_size;
 @@global.innodb_purge_batch_size
-300
+1000
 '#---------------------FN_DYNVARS_046_02-------------------------#'
 SET innodb_purge_batch_size = 1;
 ERROR HY000: Variable 'innodb_purge_batch_size' is a GLOBAL variable and should be set with SET GLOBAL
 SELECT @@innodb_purge_batch_size;
 @@innodb_purge_batch_size
-300
+1000
 SELECT local.innodb_purge_batch_size;
 ERROR 42S02: Unknown table 'local' in field list
 SET global innodb_purge_batch_size = 1;
@@ -112,4 +112,4 @@ SELECT @@global.innodb_purge_batch_size;
 SET @@global.innodb_purge_batch_size = @global_start_value;
 SELECT @@global.innodb_purge_batch_size;
 @@global.innodb_purge_batch_size
-300
+1000

mysql-test/suite/sys_vars/r/sysvars_innodb,32bit.rdiff

@@ -307,7 +307,7 @@
  NUMERIC_MAX_VALUE	65536
 @@ -1345,7 +1345,7 @@
  SESSION_VALUE	NULL
- DEFAULT_VALUE	300
+ DEFAULT_VALUE	1000
  VARIABLE_SCOPE	GLOBAL
 -VARIABLE_TYPE	BIGINT UNSIGNED
 +VARIABLE_TYPE	INT UNSIGNED

mysql-test/suite/sys_vars/r/sysvars_innodb.result

@@ -1293,7 +1293,7 @@ READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	OPTIONAL
 VARIABLE_NAME	INNODB_PURGE_BATCH_SIZE
 SESSION_VALUE	NULL
-DEFAULT_VALUE	300
+DEFAULT_VALUE	1000
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	BIGINT UNSIGNED
 VARIABLE_COMMENT	Number of UNDO log pages to purge in one batch from the history list.