Revert "MDEV-10296 - Multi-instance table cache"

This reverts commit 8613633f2648637f916b949a25d36cfea4120758.

6 files changed, 15 insertions, 87 deletions

diff --git a/mysql-test/r/mysqld--help.result b/mysql-test/r/mysqld--help.result
index cb41da1eb3a..7f15a8a7017 100644
--- a/mysql-test/r/mysqld--help.result
+++ b/mysql-test/r/mysqld--help.result
@@ -1124,7 +1124,7 @@ The following options may be given as the first argument:
  --table-open-cache=# 
  The number of cached open tables
  --table-open-cache-instances=# 
- Maximum number of table cache instances
+ The number of table cache instances
  --tc-heuristic-recover=name 
  Decision to use in heuristic recover process. One of: OFF,
  COMMIT, ROLLBACK
@@ -1512,7 +1512,7 @@ sysdate-is-now FALSE
 table-cache 431
 table-definition-cache 400
 table-open-cache 431
-table-open-cache-instances 8
+table-open-cache-instances 1
 tc-heuristic-recover OFF
 thread-cache-size 151
 thread-pool-idle-timeout 60
diff --git a/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result b/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
index 2e4db1a15a7..84fb2c2df57 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
@@ -3932,12 +3932,12 @@ READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	TABLE_OPEN_CACHE_INSTANCES
 SESSION_VALUE	NULL
-GLOBAL_VALUE	8
+GLOBAL_VALUE	1
 GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	8
+DEFAULT_VALUE	1
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	BIGINT UNSIGNED
-VARIABLE_COMMENT	Maximum number of table cache instances
+VARIABLE_COMMENT	The number of table cache instances
 NUMERIC_MIN_VALUE	1
 NUMERIC_MAX_VALUE	64
 NUMERIC_BLOCK_SIZE	1
diff --git a/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result b/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
index 52105c15ed4..3494926e99c 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
@@ -4716,12 +4716,12 @@ READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	TABLE_OPEN_CACHE_INSTANCES
 SESSION_VALUE	NULL
-GLOBAL_VALUE	8
+GLOBAL_VALUE	1
 GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	8
+DEFAULT_VALUE	1
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	BIGINT UNSIGNED
-VARIABLE_COMMENT	Maximum number of table cache instances
+VARIABLE_COMMENT	The number of table cache instances
 NUMERIC_MIN_VALUE	1
 NUMERIC_MAX_VALUE	64
 NUMERIC_BLOCK_SIZE	1
diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index b9f61f489bb..5e1df31c95b 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -3231,9 +3231,9 @@ static Sys_var_ulong Sys_table_cache_size(
        ON_UPDATE(fix_table_open_cache));
 
 static Sys_var_ulong Sys_table_cache_instances(
-       "table_open_cache_instances", "Maximum number of table cache instances",
+       "table_open_cache_instances", "The number of table cache instances",
        READ_ONLY GLOBAL_VAR(tc_instances), CMD_LINE(REQUIRED_ARG),
-       VALID_RANGE(1, 64), DEFAULT(8), BLOCK_SIZE(1));
+       VALID_RANGE(1, 64), DEFAULT(1), BLOCK_SIZE(1));
 
 static Sys_var_ulong Sys_thread_cache_size(
        "thread_cache_size",
diff --git a/sql/table.h b/sql/table.h
index 203c21a2ef0..57477e4e81d 100644
--- a/sql/table.h
+++ b/sql/table.h
@@ -1050,7 +1050,6 @@ private:
 
 public:
 
-  uint32 instance; /** Table cache instance this TABLE is belonging to */
   THD	*in_use;                        /* Which thread uses this */
 
   uchar *record[2];			/* Pointer to records */
diff --git a/sql/table_cache.cc b/sql/table_cache.cc
index 030116c7583..0e0624e5306 100644
--- a/sql/table_cache.cc
+++ b/sql/table_cache.cc
@@ -56,8 +56,6 @@
 ulong tdc_size; /**< Table definition cache threshold for LRU eviction. */
 ulong tc_size; /**< Table cache threshold for LRU eviction. */
 ulong tc_instances;
-static uint32 tc_active_instances= 1;
-static uint32 tc_contention_warning_reported;
 
 /** Data collections. */
 static LF_HASH tdc_hash; /**< Collection of TABLE_SHARE objects. */
@@ -129,12 +127,10 @@ struct Table_cache_instance
             I_P_List_null_counter, I_P_List_fast_push_back<TABLE> >
     free_tables;
   ulong records;
-  uint mutex_waits;
-  uint mutex_nowaits;
   /** Avoid false sharing between instances */
   char pad[CPU_LEVEL1_DCACHE_LINESIZE];
 
-  Table_cache_instance(): records(0), mutex_waits(0), mutex_nowaits(0)
+  Table_cache_instance(): records(0)
   {
     mysql_mutex_init(key_LOCK_table_cache, &LOCK_table_cache,
                      MY_MUTEX_INIT_FAST);
@@ -146,68 +142,6 @@ struct Table_cache_instance
     DBUG_ASSERT(free_tables.is_empty());
     DBUG_ASSERT(records == 0);
   }
-
-  /**
-    Lock table cache mutex and check contention.
-
-    Instance is considered contested if more than 20% of mutex acquisiotions
-    can't be served immediately. Up to 100 000 probes may be performed to avoid
-    instance activation on short sporadic peaks. 100 000 is estimated maximum
-    number of queries one instance can serve in one second.
-
-    These numbers work well on a 2 socket / 20 core / 40 threads Intel Broadwell
-    system, that is expected number of instances is activated within reasonable
-    warmup time. It may have to be adjusted for other systems.
-
-    Only TABLE object acquistion is instrumented. We intentionally avoid this
-    overhead on TABLE object release. All other table cache mutex acquistions
-    are considered out of hot path and are not instrumented either.
-  */
-  void lock_and_check_contention(uint32 n_instances, uint32 instance)
-  {
-    if (mysql_mutex_trylock(&LOCK_table_cache))
-    {
-      mysql_mutex_lock(&LOCK_table_cache);
-      if (++mutex_waits == 20000)
-      {
-        if (n_instances < tc_instances)
-        {
-          if (my_atomic_cas32_weak_explicit(&tc_active_instances, &n_instances,
-                                            n_instances + 1,
-                                            MY_MEMORY_ORDER_RELAXED,
-                                            MY_MEMORY_ORDER_RELAXED))
-          {
-            sql_print_information("Detected table cache mutex contention at instance %d: "
-                                  "%d%% waits. Additional table cache instance "
-                                  "activated. Number of instances after "
-                                  "activation: %d.",
-                                  instance + 1,
-                                  mutex_waits * 100 / (mutex_nowaits + mutex_waits),
-                                  n_instances + 1);
-          }
-        }
-        else if (!my_atomic_fas32_explicit(&tc_contention_warning_reported, 1,
-                                           MY_MEMORY_ORDER_RELAXED))
-        {
-          sql_print_warning("Detected table cache mutex contention at instance %d: "
-                            "%d%% waits. Additional table cache instance "
-                            "cannot be activated: consider raising "
-                            "table_open_cache_instances. Number of active "
-                            "instances: %d.",
-                            instance + 1,
-                            mutex_waits * 100 / (mutex_nowaits + mutex_waits),
-                            n_instances);
-        }
-        mutex_waits= 0;
-        mutex_nowaits= 0;
-      }
-    }
-    else if (++mutex_nowaits == 80000)
-    {
-      mutex_waits= 0;
-      mutex_nowaits= 0;
-    }
-  }
 };
 
 
@@ -353,12 +287,11 @@ void tc_purge(bool mark_flushed)
 
 void tc_add_table(THD *thd, TABLE *table)
 {
-  uint32 i= thd->thread_id % my_atomic_load32_explicit(&tc_active_instances, MY_MEMORY_ORDER_RELAXED);
+  ulong i= thd->thread_id % tc_instances;
   TABLE *LRU_table= 0;
   TDC_element *element= table->s->tdc;
 
   DBUG_ASSERT(table->in_use == thd);
-  table->instance= i;
   mysql_mutex_lock(&element->LOCK_table_share);
   /* Wait for MDL deadlock detector to complete traversing tdc.all_tables. */
   while (element->all_tables_refs)
@@ -394,12 +327,10 @@ void tc_add_table(THD *thd, TABLE *table)
 
 static TABLE *tc_acquire_table(THD *thd, TDC_element *element)
 {
-  uint32 n_instances=
-    my_atomic_load32_explicit(&tc_active_instances, MY_MEMORY_ORDER_RELAXED);
-  uint32 i= thd->thread_id % n_instances;
+  ulong i= thd->thread_id % tc_instances;
   TABLE *table;
 
-  tc[i].lock_and_check_contention(n_instances, i);
+  mysql_mutex_lock(&tc[i].LOCK_table_cache);
   table= element->free_tables[i].list.pop_front();
   if (table)
   {
@@ -444,8 +375,7 @@ static TABLE *tc_acquire_table(THD *thd, TDC_element *element)
 
 void tc_release_table(TABLE *table)
 {
-  uint32 i= table->instance;
-  DBUG_ENTER("tc_release_table");
+  ulong i= table->in_use->thread_id % tc_instances;
   DBUG_ASSERT(table->in_use);
   DBUG_ASSERT(table->file);
 
@@ -464,7 +394,6 @@ void tc_release_table(TABLE *table)
     tc[i].free_tables.push_back(table);
     mysql_mutex_unlock(&tc[i].LOCK_table_cache);
   }
-  DBUG_VOID_RETURN;
 }