Fix bug https://code.launchpad.net/~laurynas-biveinis/percona-server/bug1295268

(Inadequate background LRU flushing for write workloads with InnoDB compression).
  
  If InnoDB compression is used and the workload has writes, the
  following situation is possible. The LRU flusher issues an LRU flush
  request for an instance.  buf_do_LRU_batch decides to perform
  unzip_LRU eviction and this eviction might fully satisfy the
  request. Then buf_flush_LRU_tail checks the number of flushed pages in
  the last iteration, finds it to be zero, and wrongly decides not to
  flush that instance anymore.
  
  Fixed by maintaining unzip_LRU eviction counter in struct
  flush_counter_t variables, and checking it in buf_flush_LRU_tail when
  deciding whether to stop flushing the current instance.

Added test cases for new configuration files to get mysql-test-run suite sys_vars
to pass. Fix some small errors.

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

+select @@global.innodb_mtflush_threads;
+@@global.innodb_mtflush_threads
+8
+select @@session.innodb_mtflush_threads;
+ERROR HY000: Variable 'innodb_mtflush_threads' is a GLOBAL variable
+show global variables like 'innodb_mtflush_threads';
+Variable_name	Value
+innodb_mtflush_threads	8
+show session variables like 'innodb_mtflush_threads';
+Variable_name	Value
+innodb_mtflush_threads	8
+select * from information_schema.global_variables where variable_name='innodb_mtflush_threads';
+VARIABLE_NAME	VARIABLE_VALUE
+INNODB_MTFLUSH_THREADS	8
+select * from information_schema.session_variables where variable_name='innodb_mtflush_threads';
+VARIABLE_NAME	VARIABLE_VALUE
+INNODB_MTFLUSH_THREADS	8
+set global innodb_mtflush_threads=1;
+ERROR HY000: Variable 'innodb_mtflush_threads' is a read only variable
+set session innodb_mtflush_threads=1;
+ERROR HY000: Variable 'innodb_mtflush_threads' is a read only variable

mysql-test/suite/sys_vars/r/innodb_use_lz4_basic.result

+select @@global.innodb_use_fallocate;
+@@global.innodb_use_fallocate
+0

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

+select @@global.innodb_use_mtflush;
+@@global.innodb_use_mtflush
+0
+select @@session.innodb_use_mtflush;
+ERROR HY000: Variable 'innodb_use_mtflush' is a GLOBAL variable
+show global variables like 'innodb_use_mtflush';
+Variable_name	Value
+innodb_use_mtflush	OFF
+show session variables like 'innodb_use_mtflush';
+Variable_name	Value
+innodb_use_mtflush	OFF
+select * from information_schema.global_variables where variable_name='innodb_use_mtflush';
+VARIABLE_NAME	VARIABLE_VALUE
+INNODB_USE_MTFLUSH	OFF
+select * from information_schema.session_variables where variable_name='innodb_use_mtflush';
+VARIABLE_NAME	VARIABLE_VALUE
+INNODB_USE_MTFLUSH	OFF
+set global innodb_use_mtflush=1;
+ERROR HY000: Variable 'innodb_use_mtflush' is a read only variable
+set session innodb_use_mtflush=1;
+ERROR HY000: Variable 'innodb_use_mtflush' is a read only variable

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

+SET @start_use_trim = @@global.innodb_use_trim;
+SELECT @start_use_trim;
+@start_use_trim
+0
+SELECT COUNT(@@GLOBAL.innodb_use_trim);
+COUNT(@@GLOBAL.innodb_use_trim)
+1
+1 Expected
+SET @@GLOBAL.innodb_use_trim=1;
+SELECT COUNT(@@GLOBAL.innodb_use_trim);
+COUNT(@@GLOBAL.innodb_use_trim)
+1
+1 Expected
+SELECT IF(@@GLOBAL.innodb_use_trim, 'ON', 'OFF') = VARIABLE_VALUE
+FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES
+WHERE VARIABLE_NAME='innodb_use_trim';
+IF(@@GLOBAL.innodb_use_trim, 'ON', 'OFF') = VARIABLE_VALUE
+1
+1 Expected
+SELECT COUNT(@@GLOBAL.innodb_use_trim);
+COUNT(@@GLOBAL.innodb_use_trim)
+1
+1 Expected
+SELECT COUNT(VARIABLE_VALUE)
+FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES 
+WHERE VARIABLE_NAME='innodb_use_trim';
+COUNT(VARIABLE_VALUE)
+1
+1 Expected
+SET @@global.innodb_use_trim = @start_use_trim;
+SELECT @@global.innodb_use_trim;
+@@global.innodb_use_trim
+0

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

+--source include/have_innodb.inc
+# bool readonly
+
+#
+# show values;
+#
+select @@global.innodb_mtflush_threads;
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+select @@session.innodb_mtflush_threads;
+show global variables like 'innodb_mtflush_threads';
+show session variables like 'innodb_mtflush_threads';
+select * from information_schema.global_variables where variable_name='innodb_mtflush_threads';
+select * from information_schema.session_variables where variable_name='innodb_mtflush_threads';
+
+#
+# show that it's read-only
+#
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+set global innodb_mtflush_threads=1;
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+set session innodb_mtflush_threads=1;

mysql-test/suite/sys_vars/t/innodb_use_lz4_basic.test

+--source include/have_innodb.inc
+# bool readonly
+# not on all compilations
+select @@global.innodb_use_fallocate;
+

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

+--source include/have_innodb.inc
+# bool readonly
+
+#
+# show values;
+#
+select @@global.innodb_use_mtflush;
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+select @@session.innodb_use_mtflush;
+show global variables like 'innodb_use_mtflush';
+show session variables like 'innodb_use_mtflush';
+select * from information_schema.global_variables where variable_name='innodb_use_mtflush';
+select * from information_schema.session_variables where variable_name='innodb_use_mtflush';
+
+#
+# show that it's read-only
+#
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+set global innodb_use_mtflush=1;
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+set session innodb_use_mtflush=1;
+

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

+--source include/have_innodb.inc
+
+SET @start_use_trim = @@global.innodb_use_trim;
+SELECT @start_use_trim;
+
+SELECT COUNT(@@GLOBAL.innodb_use_trim);
+--echo 1 Expected
+
+####################################################################
+#   Check if Value can set                                         #
+####################################################################
+
+SET @@GLOBAL.innodb_use_trim=1;
+
+SELECT COUNT(@@GLOBAL.innodb_use_trim);
+--echo 1 Expected
+
+#################################################################
+# Check if the value in GLOBAL Table matches value in variable  #
+#################################################################
+
+SELECT IF(@@GLOBAL.innodb_use_trim, 'ON', 'OFF') = VARIABLE_VALUE
+FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES
+WHERE VARIABLE_NAME='innodb_use_trim';
+--echo 1 Expected
+
+SELECT COUNT(@@GLOBAL.innodb_use_trim);
+--echo 1 Expected
+
+SELECT COUNT(VARIABLE_VALUE)
+FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES 
+WHERE VARIABLE_NAME='innodb_use_trim';
+--echo 1 Expected
+
+SET @@global.innodb_use_trim = @start_use_trim;
+SELECT @@global.innodb_use_trim;
\ No newline at end of file

storage/innobase/handler/ha_innodb.cc

@@ -16801,7 +16801,7 @@ static MYSQL_SYSVAR_BOOL(use_lz4, srv_use_lz4,
 #endif /* HAVE_LZ4 */
 
 static MYSQL_SYSVAR_LONG(mtflush_threads, srv_mtflush_threads,
-  PLUGIN_VAR_RQCMDARG,
+  PLUGIN_VAR_NOCMDARG | PLUGIN_VAR_READONLY,
   "Number of multi-threaded flush threads",
   NULL, NULL,
   MTFLUSH_DEFAULT_WORKER, /* Default setting */
@@ -16810,7 +16810,7 @@ static MYSQL_SYSVAR_LONG(mtflush_threads, srv_mtflush_threads,
   0);
 
 static MYSQL_SYSVAR_BOOL(use_mtflush, srv_use_mtflush,
-  PLUGIN_VAR_OPCMDARG ,
+  PLUGIN_VAR_NOCMDARG | PLUGIN_VAR_READONLY,
   "Use multi-threaded flush. Default FALSE.",
   NULL, NULL, FALSE);
 

storage/xtradb/buf/buf0flu.cc

@@ -1549,6 +1549,7 @@ buf_flush_LRU_list_batch(
 
 	n->flushed = 0;
 	n->evicted = 0;
+	n->unzip_LRU_evicted = 0;
 
 	ut_ad(mutex_own(&buf_pool->LRU_list_mutex));
 
@@ -1660,21 +1661,22 @@ buf_do_LRU_batch(
 	flush_counters_t*	n)	/*!< out: flushed/evicted page
 					counts */
 {
-	ulint	count = 0;
-
 	if (buf_LRU_evict_from_unzip_LRU(buf_pool)) {
-		count += buf_free_from_unzip_LRU_list_batch(buf_pool, max);
+		n->unzip_LRU_evicted
+			+= buf_free_from_unzip_LRU_list_batch(buf_pool, max);
+	} else {
+		n->unzip_LRU_evicted = 0;
 	}
 
-	if (max > count) {
-		buf_flush_LRU_list_batch(buf_pool, max - count, limited_scan,
-					 n);
+	if (max > n->unzip_LRU_evicted) {
+		buf_flush_LRU_list_batch(buf_pool, max - n->unzip_LRU_evicted,
+					 limited_scan, n);
 	} else {
 		n->evicted = 0;
 		n->flushed = 0;
 	}
 
-	n->flushed += count;
+	n->evicted += n->unzip_LRU_evicted;
 }
 
 /*******************************************************************//**
@@ -2306,9 +2308,15 @@ buf_flush_LRU_tail(void)
 
 				requested_pages[i] += lru_chunk_size;
 
+				/* If we failed to flush or evict this
+				instance, do not bother anymore. But take into
+			        account that we might have zero flushed pages
+				because the flushing request was fully
+				satisfied by unzip_LRU evictions. */
 				if (requested_pages[i] >= scan_depth[i]
 				    || !(srv_cleaner_eviction_factor
-					 ? n.evicted : n.flushed)) {
+					? n.evicted
+					: (n.flushed + n.unzip_LRU_evicted))) {
 
 					active_instance[i] = false;
 					remaining_instances--;

storage/xtradb/handler/ha_innodb.cc

@@ -17955,7 +17955,7 @@ static MYSQL_SYSVAR_BOOL(use_lz4, srv_use_lz4,
 #endif /* HAVE_LZ4 */
 
 static MYSQL_SYSVAR_LONG(mtflush_threads, srv_mtflush_threads,
-  PLUGIN_VAR_RQCMDARG,
+  PLUGIN_VAR_NOCMDARG | PLUGIN_VAR_READONLY,
   "Number of multi-threaded flush threads",
   NULL, NULL,
   MTFLUSH_DEFAULT_WORKER, /* Default setting */
@@ -17964,7 +17964,7 @@ static MYSQL_SYSVAR_LONG(mtflush_threads, srv_mtflush_threads,
   0);
 
 static MYSQL_SYSVAR_BOOL(use_mtflush, srv_use_mtflush,
-  PLUGIN_VAR_OPCMDARG ,
+  PLUGIN_VAR_NOCMDARG | PLUGIN_VAR_READONLY,
   "Use multi-threaded flush. Default FALSE.",
   NULL, NULL, FALSE);
 

storage/xtradb/include/buf0flu.h

@@ -40,6 +40,8 @@ extern ibool buf_page_cleaner_is_active;
 struct flush_counters_t {
 	ulint	flushed;	/*!< number of dirty pages flushed */
 	ulint	evicted;	/*!< number of clean pages evicted */
+	ulint	unzip_LRU_evicted;/*!< number of uncompressed page images
+				evicted */
 };