Backport:

B-g#24795: SHOW PROFILE implementation

Don't use memory roots to store profiling information, because
memory roots make freeing the data a no-op, and thus long-running
processes with profiling turned on the whole time could eventually 
use all available memory.

Instead, use regular heap allocation and deallocation calls to 
manage profiling data.  Replace the leaky List usage with a similar-
behaving structure named "Queue".


sql/sql_profile.cc:
  Don't use C++ iterators on our simple Queue implementation.  They're
  not implemented and we don't really need them.
  
  Rip out idea of swapping out the thd's mem_root.
sql/sql_profile.h:
  Rip out idea of needing a mem_root.
  
  Implement a Queue that looks and behaves very similarly to memroot-
  using List.

sql/sql_profile.cc

@@ -175,11 +175,8 @@ void QUERY_PROFILE::set_query_source(char *query_source_arg,
 
 QUERY_PROFILE::~QUERY_PROFILE()
 {
-  PROFILE_ENTRY *entry;
-  List_iterator<PROFILE_ENTRY> it(entries);
-  while ((entry= it++) != NULL)
-    delete entry;
-  entries.empty();
+  while (! entries.is_empty())
+    delete entries.pop();
 
   if (query_source != NULL)
     my_free(query_source, MYF(0));
@@ -191,7 +188,6 @@ void QUERY_PROFILE::status(const char *status_arg,
 {
   THD *thd= profiling->thd;
   PROFILE_ENTRY *prof;
-  MEM_ROOT *saved_mem_root;
   DBUG_ENTER("QUERY_PROFILE::status");
 
   /* Blank status.  Just return, and thd->proc_info will be set blank later. */
@@ -210,22 +206,6 @@ void QUERY_PROFILE::status(const char *status_arg,
   if (unlikely((thd->query_id != server_query_id) && !thd->spcont))
     reset();
     
-  /*
-    In order to keep the profile information between queries (i.e. from
-    SELECT to the following SHOW PROFILE command) the following code is
-    necessary to keep the profile from getting freed automatically when
-    mysqld cleans up after the query.
-
-    The "entries" list allocates is memory from the current thd's mem_root.
-    We substitute our mem_root temporarily so that we intercept those
-    allocations into our own mem_root.
-    
-    The thd->mem_root structure is freed after each query is completed,
-    so temporarily override it.
-  */
-  saved_mem_root= thd->mem_root;
-  thd->mem_root= &profiling->mem_root;
-
   if (function_arg && file_arg) 
   {
     if ((profile_end= prof= new PROFILE_ENTRY(this, status_arg, function_arg, 
@@ -238,9 +218,6 @@ void QUERY_PROFILE::status(const char *status_arg,
       entries.push_back(prof);
   }
 
-  /* Restore mem_root */
-  thd->mem_root= saved_mem_root;
-
   DBUG_VOID_RETURN;
 }
 
@@ -252,11 +229,8 @@ void QUERY_PROFILE::reset()
     server_query_id= profiling->thd->query_id; /* despite name, is global */
     profile_start.collect();
 
-    PROFILE_ENTRY *entry;
-    List_iterator<PROFILE_ENTRY> it(entries);
-    while ((entry= it++) != NULL)
-      delete entry;
-    entries.empty();
+    while (! entries.is_empty())
+      delete entries.pop();
   }
   DBUG_VOID_RETURN;
 }
@@ -344,10 +318,14 @@ bool QUERY_PROFILE::show(uint options)
   struct rusage *last_rusage= &(profile_start.rusage);
 #endif
 
-  List_iterator<PROFILE_ENTRY> it(entries);
   PROFILE_ENTRY *entry;
-  while ((entry= it++) != NULL)
+  void *iterator;
+  for (iterator= entries.new_iterator(); 
+       iterator != NULL; 
+       iterator= entries.iterator_next(iterator))
   {
+    entry= entries.iterator_value(iterator);
+
 #ifdef HAVE_GETRUSAGE
     struct rusage *rusage= &(entry->rusage);
 #endif
@@ -463,24 +441,15 @@ bool QUERY_PROFILE::show(uint options)
 PROFILING::PROFILING()
   :profile_id_counter(0), keeping(1), current(NULL), last(NULL)
 {
-  init_sql_alloc(&mem_root,
-                 PROFILE_ALLOC_BLOCK_SIZE,
-                 PROFILE_ALLOC_PREALLOC_SIZE);
 }
 
 PROFILING::~PROFILING()
 {
-  QUERY_PROFILE *prof;
-
-  List_iterator<QUERY_PROFILE> it(history);
-  while ((prof= it++) != NULL)
-    delete prof;
-  history.empty();
+  while (! history.is_empty())
+    delete history.pop();
 
   if (current != NULL)
     delete current;
-
-  free_root(&mem_root, MYF(0));
 }
 
 void PROFILING::status_change(const char *status_arg,
@@ -505,7 +474,6 @@ void PROFILING::status_change(const char *status_arg,
 
 void PROFILING::store()
 {
-  MEM_ROOT *saved_mem_root;
   DBUG_ENTER("PROFILING::store");
 
   /* Already stored */
@@ -517,21 +485,7 @@ void PROFILING::store()
   }
 
   while (history.elements > thd->variables.profiling_history_size)
-  {
-    QUERY_PROFILE *tmp= history.pop();
-    delete tmp;
-  }
-
-  /* 
-    Switch out memory roots so that we're sure that we keep what we need 
-    
-    The "history" list implementation allocates its memory in the current 
-    thd's mem_root.  We substitute our mem_root temporarily so that we
-    intercept those allocations into our own mem_root.
-  */
-
-  saved_mem_root= thd->mem_root;
-  thd->mem_root= &mem_root;
+    delete history.pop();
 
   if (current != NULL)
   {
@@ -556,9 +510,6 @@ void PROFILING::store()
   DBUG_ASSERT(current == NULL);
   current= new QUERY_PROFILE(this, thd->query, thd->query_length);
 
-  /* Restore memory root */
-  thd->mem_root= saved_mem_root;
-
   DBUG_VOID_RETURN;
 }
 
@@ -598,9 +549,13 @@ bool PROFILING::show_profiles()
 
   unit->set_limit(sel);
   
-  List_iterator<QUERY_PROFILE> it(history);
-  while ((prof= it++) != NULL)
+  void *iterator;
+  for (iterator= history.new_iterator(); 
+       iterator != NULL; 
+       iterator= history.iterator_next(iterator))
   {
+    prof= history.iterator_value(iterator);
+
     String elapsed;
 
     PROFILE_ENTRY *ps= &prof->profile_start;
@@ -651,9 +606,13 @@ bool PROFILING::show(uint options, uint profiling_query_id)
   DBUG_ENTER("PROFILING::show");
   QUERY_PROFILE *prof;
 
-  List_iterator<QUERY_PROFILE> it(history);
-  while ((prof= it++) != NULL)
+  void *iterator;
+  for (iterator= history.new_iterator(); 
+       iterator != NULL; 
+       iterator= history.iterator_next(iterator))
   {
+    prof= history.iterator_value(iterator);
+
     if(prof->profiling_query_id == profiling_query_id)
       DBUG_RETURN(prof->show(options));
   }
@@ -681,11 +640,15 @@ int PROFILING::fill_statistics_info(THD *thd, struct st_table_list *tables, Item
   TABLE *table= tables->table;
   ulonglong row_number= 0;
 
-  List_iterator<QUERY_PROFILE> query_it(history);
   QUERY_PROFILE *query;
   /* Go through each query in this thread's stored history... */
-  while ((query= query_it++) != NULL)
+  void *history_iterator;
+  for (history_iterator= history.new_iterator(); 
+       history_iterator != NULL; 
+       history_iterator= history.iterator_next(history_iterator))
   {
+    query= history.iterator_value(history_iterator);
+
     PROFILE_ENTRY *ps= &(query->profile_start);
     double last_time= ps->time_usecs;
 #ifdef HAVE_GETRUSAGE
@@ -699,16 +662,20 @@ int PROFILING::fill_statistics_info(THD *thd, struct st_table_list *tables, Item
     */
     ulonglong seq;
 
-    List_iterator<PROFILE_ENTRY> step_it(query->entries);
+    void *entry_iterator;
     PROFILE_ENTRY *entry;
     /* ...and for each query, go through all its state-change steps. */
-    for (seq= 0, entry= step_it++; 
-         entry != NULL; 
+    for (seq= 0, entry_iterator= query->entries.new_iterator(); 
+         entry_iterator != NULL; 
+         entry_iterator= query->entries.iterator_next(entry_iterator),
 #ifdef HAVE_GETRUSAGE
          last_rusage= &(entry->rusage),
 #endif
-         seq++, last_time= entry->time_usecs, entry= step_it++, row_number++)
+         seq++, last_time= entry->time_usecs, row_number++)
     {
+      entry= query->entries.iterator_value(entry_iterator);
+
+
       /* Set default values for this row. */
       restore_record(table, s->default_values);
 

sql/sql_profile.h

@@ -83,6 +83,112 @@ class QUERY_PROFILE;
 class PROFILING;
 
 
+/**
+  Implements a persistent FIFO using server List method names.  Not
+  thread-safe.  Intended to be used on thread-local data only.  
+*/
+template <class T> class Queue
+{
+private:
+
+  struct queue_item
+  {
+    T *payload;
+    struct queue_item *next, *previous;
+  };
+
+  struct queue_item *first, *last;
+
+public:
+  Queue()
+  {
+    elements= 0;
+    first= last= NULL;
+  }
+
+  void empty()
+  {
+    struct queue_item *i, *after_i;
+    for (i= first; i != NULL; i= after_i)
+    {
+      after_i= i->next;
+      my_free((char *) i, MYF(0));
+    }
+    elements= 0;
+  }
+
+  ulong elements;                       /* The count of items in the Queue */
+
+  void push_back(T *payload)
+  {
+    struct queue_item *new_item;
+
+    new_item= (struct queue_item *) my_malloc(sizeof(struct queue_item), MYF(0));
+
+    new_item->payload= payload;
+
+    if (first == NULL)
+      first= new_item;
+    if (last != NULL)
+    {
+      DBUG_ASSERT(last->next == NULL);
+      last->next= new_item;
+    }
+    new_item->previous= last;
+    new_item->next= NULL;
+    last= new_item;
+
+    elements++;
+  }
+
+  T *pop()
+  {
+    struct queue_item *old_item= first;
+    T *ret= NULL;
+
+    if (first == NULL)
+    {
+      DBUG_PRINT("warning", ("tried to pop nonexistent item from Queue"));
+      return NULL;
+    }
+
+    ret= old_item->payload;
+    if (first->next != NULL)
+      first->next->previous= NULL;
+    else
+      last= NULL;
+    first= first->next;
+
+    my_free((char *)old_item, MYF(0));
+    elements--;
+
+    return ret;
+  }
+
+  bool is_empty()
+  {
+    DBUG_ASSERT(((elements > 0) && (first != NULL)) || ((elements == 0) || (first == NULL)));
+    return (elements == 0);
+  }
+
+  void *new_iterator()
+  {
+    return first;
+  }
+
+  void *iterator_next(void *current)
+  {
+    return ((struct queue_item *) current)->next;
+  }
+
+  T *iterator_value(void *current)
+  {
+    return ((struct queue_item *) current)->payload;
+  }
+
+};
+
+
 /**
   A single entry in a single profile.
 */
@@ -135,7 +241,7 @@ class QUERY_PROFILE
   char *query_source;
   PROFILE_ENTRY profile_start;
   PROFILE_ENTRY *profile_end;
-  List<PROFILE_ENTRY> entries;
+  Queue<PROFILE_ENTRY> entries;
 
 
   QUERY_PROFILE(PROFILING *profiling_arg, char *query_source_arg, uint query_length_arg);
@@ -169,13 +275,12 @@ class PROFILING
     Not the system query_id, but a counter unique to profiling. 
   */
   query_id_t profile_id_counter;     
-  MEM_ROOT mem_root;
   THD *thd;
   bool keeping;
 
   QUERY_PROFILE *current;
   QUERY_PROFILE *last;
-  List<QUERY_PROFILE> history;
+  Queue<QUERY_PROFILE> history;
  
   query_id_t next_profile_id() { return(profile_id_counter++); }