MDEV-37672: Remove innodb_trx_rseg_n_slots_debug

The debug parameter innodb_trx_rseg_n_slots_debug is not compatible
with the bug fix that was implemented in MDEV-30671 and last revised
in MDEV-33213, which leads to bogus assertion failures in
trx_assign_rseg_low(), regarding look_for_rollover. When needed,
this parameter can be better simulated by adding a DBUG_EXECUTE_IF to
trx_undo_seg_create() or one of its callers.

Author: dr-m

mysql-test/suite/innodb/r/innodb_bug12400341.result

@@ -491,7 +491,6 @@ insert into test.sanity values
   ("JUNK: GLOBAL-ONLY", "I_S.SESSION_VARIABLES", "INNODB_SYNC_SPIN_LOOPS"),
   ("JUNK: GLOBAL-ONLY", "I_S.SESSION_VARIABLES", "INNODB_TEMP_DATA_FILE_PATH"),
   ("JUNK: GLOBAL-ONLY", "I_S.SESSION_VARIABLES", "INNODB_TRX_PURGE_VIEW_UPDATE_ONLY_DEBUG"),
-  ("JUNK: GLOBAL-ONLY", "I_S.SESSION_VARIABLES", "INNODB_TRX_RSEG_N_SLOTS_DEBUG"),
   ("JUNK: GLOBAL-ONLY", "I_S.SESSION_VARIABLES", "INNODB_UNDO_DIRECTORY"),
   ("JUNK: GLOBAL-ONLY", "I_S.SESSION_VARIABLES", "INNODB_UNDO_LOG_TRUNCATE"),
   ("JUNK: GLOBAL-ONLY", "I_S.SESSION_VARIABLES", "INNODB_UNDO_TABLESPACES"),

mysql-test/suite/innodb/t/innodb_bug12400341.test

@@ -1663,18 +1663,6 @@ NUMERIC_BLOCK_SIZE	NULL
 ENUM_VALUE_LIST	OFF,ON
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	NULL
-VARIABLE_NAME	INNODB_TRX_RSEG_N_SLOTS_DEBUG
-SESSION_VALUE	NULL
-DEFAULT_VALUE	0
-VARIABLE_SCOPE	GLOBAL
-VARIABLE_TYPE	INT UNSIGNED
-VARIABLE_COMMENT	Debug flags for InnoDB to limit TRX_RSEG_N_SLOTS for trx_rsegf_undo_find_free()
-NUMERIC_MIN_VALUE	0
-NUMERIC_MAX_VALUE	1024
-NUMERIC_BLOCK_SIZE	0
-ENUM_VALUE_LIST	NULL
-READ_ONLY	NO
-COMMAND_LINE_ARGUMENT	NULL
 VARIABLE_NAME	INNODB_UNDO_DIRECTORY
 SESSION_VALUE	NULL
 DEFAULT_VALUE	

mysql-test/suite/perfschema/t/show_sanity.test

@@ -19623,11 +19623,6 @@ static MYSQL_SYSVAR_ENUM(default_row_format, innodb_default_row_format,
   &innodb_default_row_format_typelib);
 
 #ifdef UNIV_DEBUG
-static MYSQL_SYSVAR_UINT(trx_rseg_n_slots_debug, trx_rseg_n_slots_debug,
-  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_NOCMDOPT,
-  "Debug flags for InnoDB to limit TRX_RSEG_N_SLOTS for trx_rsegf_undo_find_free()",
-  NULL, NULL, 0, 0, 1024, 0);
-
 static MYSQL_SYSVAR_UINT(limit_optimistic_insert_debug,
   btr_cur_limit_optimistic_insert_debug, PLUGIN_VAR_RQCMDARG,
   "Artificially limit the number of records per B-tree page (0=unlimited).",
@@ -19900,7 +19895,6 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(compression_pad_pct_max),
   MYSQL_SYSVAR(default_row_format),
 #ifdef UNIV_DEBUG
-  MYSQL_SYSVAR(trx_rseg_n_slots_debug),
   MYSQL_SYSVAR(limit_optimistic_insert_debug),
   MYSQL_SYSVAR(trx_purge_view_update_only_debug),
   MYSQL_SYSVAR(evict_tables_on_commit_debug),

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

@@ -70,11 +70,6 @@ inline buf_block_t *trx_sysf_get(mtr_t* mtr, bool rw= true)
                       0, rw ? RW_X_LATCH : RW_S_LATCH, mtr);
 }
 
-#ifdef UNIV_DEBUG
-/* Flag to control TRX_RSEG_N_SLOTS behavior debugging. */
-extern uint			trx_rseg_n_slots_debug;
-#endif
-
 /** Write DB_TRX_ID.
 @param[out]	db_trx_id	the DB_TRX_ID field to be written to
 @param[in]	id		transaction ID */

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

@@ -437,7 +437,6 @@ inline dberr_t purge_sys_t::iterator::free_history_rseg(trx_rseg_t &rseg) const
       rollback segment. */
 
       if (!(rseg.SKIP & rseg_ref) && !freed &&
-          ut_d(!trx_rseg_n_slots_debug &&)
           &rseg == &trx_sys.rseg_array[purge_sys.skipped_rseg])
         /* If rseg.space == purge_sys.truncate_undo_space.current
         the following will be a no-op. A possible conflict

mysql-test/suite/sys_vars/t/innodb_trx_rseg_n_slots_debug_basic.test

@@ -45,9 +45,6 @@ Created 3/26/1996 Heikki Tuuri
 trx_sys_t		trx_sys;
 
 #ifdef UNIV_DEBUG
-/* Flag to control TRX_RSEG_N_SLOTS behavior debugging. */
-uint	trx_rseg_n_slots_debug = 0;
-
 void rw_trx_hash_t::validate_element(trx_t *trx)
 {
   ut_ad(!trx->read_only || !trx->rsegs.m_redo.rseg);