- WL#6965: Truncate UNDO logs.

  - Change the name of from srv_undo_purge_lag to
    srv_purge_rseg_truncate_frequency in order to reflect what it
    exactly does.

  - Beside this there is also change in how this value is used.
    - On start undo_trunc cache the truncate frequency.
    - When tablespace is marked for truncate this undo_trunc cached
      value is set to 1 on completion it is restored back to global
      value.
    - Frequency of rseg truncate is
      min(undo_trunc cached frequency, global value)

    This ensures when tablespace is marked for truncate we acclerate
    rseg purge in turn truncate action and make the tablespace/rsegs
    active asap.

Author: Krunal Bauskar krunal.bauskar@oracle.com

mysql-test/suite/innodb_undo/t/innodb_wl6965-master.opt

@@ -1 +1 @@
---innodb_undo_tablespaces=2 --innodb_undo_logs=35 --innodb_max_undo_log_size=10M --innodb_undo_purge_lag=1
+--innodb_undo_tablespaces=2 --innodb_undo_logs=35 --innodb_max_undo_log_size=10M --innodb_purge_rseg_truncate_frequency=1

mysql-test/suite/innodb_undo/t/innodb_wl6965.test

@@ -12,7 +12,7 @@
 --source include/have_undo_tablespaces.inc
 
 # TC check if truncate is completed in given time frame. When
-# test is run under valgrind there is no such time assurance. 
+# test is run under valgrind there is no such time assurance.
 --source include/not_valgrind.inc
 
 

mysql-test/suite/innodb_undo/t/innodb_wl6965_1-master.opt

@@ -1 +1 @@
---innodb_undo_tablespaces=2 --innodb_undo_logs=35 --innodb_max_undo_log_size=10M --innodb_undo_purge_lag=1
+--innodb_undo_tablespaces=2 --innodb_undo_logs=35 --innodb_max_undo_log_size=10M --innodb_purge_rseg_truncate_frequency=1

mysql-test/suite/innodb_undo/t/innodb_wl6965_2-master.opt

@@ -1 +1 @@
---innodb_undo_tablespaces=2 --innodb_max_undo_log_size=10M --innodb_undo_purge_lag=1
+--innodb_undo_tablespaces=2 --innodb_max_undo_log_size=10M --innodb_purge_rseg_truncate_frequency=1

mysql-test/suite/innodb_undo/t/innodb_wl6965_crash-master.opt

@@ -1 +1 @@
---innodb_undo_tablespaces=2 --innodb_undo_logs=35 --innodb_max_undo_log_size=10M --innodb_undo_purge_lag=1
+--innodb_undo_tablespaces=2 --innodb_undo_logs=35 --innodb_max_undo_log_size=10M --innodb_purge_rseg_truncate_frequency=1

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

@@ -93,8 +93,3 @@ SELECT COUNT(@@SESSION.innodb_max_undo_log_size);
 SELECT COUNT(@@GLOBAL.innodb_max_undo_log_size);
 --echo 1 Expected
 
---Error ER_BAD_FIELD_ERROR
-SELECT innodb_max_undo_log_size = @@SESSION.innodb_max_undo_log_size;
---echo Expected error 'Readonly variable'
-
-

storage/innobase/fil/fil0fil.cc

@@ -2942,7 +2942,6 @@ fil_truncate_tablespace(
 	/* Step-2: Invalidate buffer pool pages belonging to the tablespace
 	to re-create. Remove all insert buffer entries for the tablespace */
 	buf_LRU_flush_or_remove_pages(space_id, BUF_REMOVE_ALL_NO_WRITE, 0);
-	ibuf_delete_for_discarded_space(space_id);
 
 	/* Step-3: Truncate the tablespace and accordingly update
 	the fil_space_t handler that is used to access this tablespace. */

storage/innobase/handler/ha_innodb.cc

@@ -16594,10 +16594,11 @@ static MYSQL_SYSVAR_LONGLONG(max_undo_log_size, innobase_max_undo_log_size,
   10 * 1024 * 1024L,
   LONGLONG_MAX, 1024 * 1024L);
 
-static MYSQL_SYSVAR_ULONG(undo_purge_lag, srv_undo_purge_lag,
+static MYSQL_SYSVAR_ULONG(purge_rseg_truncate_frequency,
+  srv_purge_rseg_truncate_frequency,
   PLUGIN_VAR_OPCMDARG,
   "Dictates rate at which UNDO records are purged. Value N means"
-  " purge on every Nth iteration of purge invocation",
+  " purge rollback segment(s) on every Nth iteration of purge invocation",
   NULL, NULL, 128, 1, 128, 0);
 
 /* Alias for innodb_undo_logs, this config variable is deprecated. */
@@ -16939,7 +16940,7 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(cmp_per_index_enabled),
   MYSQL_SYSVAR(undo_logs),
   MYSQL_SYSVAR(max_undo_log_size),
-  MYSQL_SYSVAR(undo_purge_lag),
+  MYSQL_SYSVAR(purge_rseg_truncate_frequency),
   MYSQL_SYSVAR(rollback_segments),
   MYSQL_SYSVAR(undo_directory),
   MYSQL_SYSVAR(undo_tablespaces),

storage/innobase/include/srv0srv.h

@@ -239,7 +239,7 @@ extern ulong	srv_undo_logs;
 extern ulong	srv_max_undo_log_size;
 
 /** Rate at which UNDO records should be purged. */
-extern ulong	srv_undo_purge_lag;
+extern ulong	srv_purge_rseg_truncate_frequency;
 
 /** UNDO logs not redo logged, these logs reside in the temp tablespace.*/
 extern const ulong	srv_tmp_undo_logs;

storage/innobase/include/trx0purge.h

@@ -399,7 +399,8 @@ class undo_trunc_t {
 		m_undo_for_trunc(ULINT_UNDEFINED),
 		m_rseg_for_trunc(),
 		m_scan_start(1),
-		m_purge_lag()
+		m_purge_rseg_truncate_frequency(
+			srv_purge_rseg_truncate_frequency)
 	{
 		/* Do Nothing. */
 	}
@@ -422,6 +423,11 @@ class undo_trunc_t {
 			/* Note: UNDO tablespace ids starts from 1. */
 			m_scan_start = 1;
 		}
+
+		/* We found a UNDO-tablespace to truncate so set the
+		local purge rseg truncate frequency to 1. This will help
+		accelerate the purge action and in turn truncate action. */
+		m_purge_rseg_truncate_frequency = 1;
 	}
 
 	/** Get the tablespace marked for truncate.
@@ -460,6 +466,11 @@ class undo_trunc_t {
 	{
 		m_undo_for_trunc = ULINT_UNDEFINED;
 		m_rseg_for_trunc.clear();
+
+		/* Sync with global value as we are done with
+		truncate now. */
+		m_purge_rseg_truncate_frequency =
+			srv_purge_rseg_truncate_frequency;
 	}
 
 	/** Get the tablespace id to start scanning from.
@@ -502,18 +513,11 @@ class undo_trunc_t {
 			s_spaces_to_truncate.end() ? false : true);
 	}
 
-	/** Cache Purge Lag.
-	@param[in]	purge_lag	original server purge lag */
-	void set_purge_lag(ulint purge_lag)
-	{
-		m_purge_lag = purge_lag;
-	}
-
-	/** Get purge lag.
-	@return cached purge lag. */
-	ulint get_purge_lag()
+	/** Get local rseg purge truncate frequency
+	@return rseg purge truncate frequency. */
+	ulint get_rseg_truncate_frequency() const
 	{
-		return(m_purge_lag);
+		return(m_purge_rseg_truncate_frequency);
 	}
 
 public:
@@ -535,8 +539,11 @@ class undo_trunc_t {
 	This is to avoid bias selection of one tablespace always. */
 	ulint			m_scan_start;
 
-	/** Purge Lag. */
-	ulint			m_purge_lag;
+	/** Rollback segment(s) purge frequency. This is local
+	value maintained along with global value. It is set to global
+	value on start but when tablespace is marked for truncate it is
+	updated to 1 and then minimum value among 2 is used by purge action. */
+	ulint			m_purge_rseg_truncate_frequency;
 };
 
 /** The control structure used in the purge operation */

storage/innobase/srv/srv0srv.cc

@@ -106,7 +106,7 @@ ulint	srv_undo_tablespaces_open = 8;
 ulong	srv_undo_logs = 1;
 
 /** Rate at which UNDO records should be purged. */
-ulong	srv_undo_purge_lag = 128;
+ulong	srv_purge_rseg_truncate_frequency = 128;
 
 /** Maximum size of undo tablespace. */
 ulong	srv_max_undo_log_size;
@@ -2434,8 +2434,14 @@ srv_do_purge(
 		n_pages_purged = trx_purge(
 			n_use_threads, srv_purge_batch_size, false);
 
+		ulint	undo_trunc_freq =
+			purge_sys->undo_trunc.get_rseg_truncate_frequency();	
 
-		if (!(count++ % srv_undo_purge_lag)) {
+		ulint	rseg_truncate_frequency =
+			ut_min(srv_purge_rseg_truncate_frequency,
+			       undo_trunc_freq);
+
+		if (!(count++ % rseg_truncate_frequency)) {
 			/* Force a truncate of the history list. */
 			n_pages_purged += trx_purge(
 				1, srv_purge_batch_size, true);

storage/innobase/trx/trx0purge.cc

@@ -683,8 +683,6 @@ trx_purge_mark_undo_for_truncate(
 		"UNDO tablespace with space identifier " ULINTPF
 		" marked for truncate", undo_trunc->get_undo_mark_for_trunc());
 #endif /* UNIV_DEBUG */
-	undo_trunc->set_purge_lag(srv_undo_purge_lag);
-	srv_undo_purge_lag = 1;
 
 	/* Step-3: Iterate over all the rsegs of selected UNDO tablespace
 	and mark them temporarily unavailable for allocation.*/
@@ -929,7 +927,6 @@ trx_purge_initiate_truncate(
 
 	undo_trunc->reset();
 	undo_trunc_t::clear_trunc_list();
-	srv_undo_purge_lag = undo_trunc->get_purge_lag();
 
 	DBUG_EXECUTE_IF("ib_undo_trunc_trunc_done",
 			ib_logf(IB_LOG_LEVEL_INFO, "ib_undo_trunc_trunc_done");