Address review feedback

- One iterator class
- Switch back from state automaton into two-nested-iterators approach..

mysql-test/t/join_nested.test

@@ -462,7 +462,6 @@ SELECT t2.a,t2.b,t3.a,t3.b,t4.a,t4.b
        LEFT JOIN              
        (t1,t2)
        ON t3.a=1 AND t3.b=t2.b AND t2.b=t4.b;
-
 SELECT t2.a,t2.b,t3.a,t3.b,t4.a,t4.b
   FROM (t3,t4)
        LEFT JOIN              

mysql-test/t/subselect_sj2.test

@@ -586,6 +586,7 @@ if (`select @@join_cache_level=6`)
   --echo # Not anymore:
   --echo # The following query gives wrong result due to Bug#49129
 }
+select sin(0);
 select * from t0 where t0.a in 
   (select t1.a from t1, t2 where t2.a=t0.a and t1.b=t2.b);
 

sql/multi_range_read.cc

@@ -682,7 +682,7 @@ void DsMrr_impl::setup_buffer_sizes(key_range *sample_key)
   {
     /* Give all space to forward key buffer. */
     key_buffer= &forward_key_buf;
-    identical_key_it= &forward_key_it;
+    //identical_key_it= &forward_key_it;
     key_buffer->set_buffer_space(full_buf, full_buf_end);
 
     /* Just in case, tell rowid buffer that it has zero size: */
@@ -731,7 +731,7 @@ void DsMrr_impl::setup_buffer_sizes(key_range *sample_key)
   rowid_buffer_end= full_buf + bytes_for_rowids;
   rowid_buffer.set_buffer_space(full_buf, rowid_buffer_end);
   key_buffer= &backward_key_buf;
-  identical_key_it= &backward_key_it;
+  //identical_key_it= &backward_key_it;
   key_buffer->set_buffer_space(rowid_buffer_end, full_buf_end); 
 }
 
@@ -771,7 +771,7 @@ void DsMrr_impl::dsmrr_fill_key_buffer()
       */
       rowid_buffer.set_buffer_space(full_buf, rowid_buffer_end);
       key_buffer= &backward_key_buf;
-      identical_key_it= &backward_key_it;
+      //identical_key_it= &backward_key_it;
       key_buffer->set_buffer_space(rowid_buffer_end, full_buf_end);
     }
     key_buffer->reset();
@@ -815,9 +815,12 @@ void DsMrr_impl::dsmrr_fill_key_buffer()
                             is_mrr_assoc? (uchar**)&cur_range_info: NULL,
                             sizeof(void*));
 
-  last_identical_key_ptr= NULL;
+  //last_identical_key_ptr= NULL;
   //in_identical_keys_range= FALSE;
-  index_scan_state= GET_NEXT_RANGE;
+  //index_scan_state= GET_NEXT_RANGE;
+  scanning_key_val_iter= FALSE;
+  index_scan_eof= FALSE; 
+
   DBUG_VOID_RETURN;
 }
 
@@ -834,22 +837,88 @@ void DsMrr_impl::reallocate_buffer_space()
 }
 
 
-/**
-  Read out ranges from the buffer until we've reached the range with 
-  last_identical_key_ptr. 
-*/
+//////////////////////////////////////////////////////////////////////////////
+//////////////////////////////////////////////////////////////////////////////
+bool Key_value_records_iterator::init(DsMrr_impl *dsmrr_arg)
+{
+  int res;
+  dsmrr= dsmrr_arg;
+  handler *file= dsmrr->do_rndpos_scan? dsmrr->h2 : dsmrr->h;
+
+  identical_key_it.init(dsmrr->key_buffer);
+  /* Get the first pair into (cur_index_tuple, cur_range_info) */ 
+  if (identical_key_it.read())
+    return TRUE;
+
+  uchar *key_in_buf= dsmrr->cur_index_tuple;
+
+  if (dsmrr->use_key_pointers)
+    dsmrr->cur_index_tuple= *((uchar**)dsmrr->cur_index_tuple);
+  
+  /* Check out how many more identical keys are following */
+  //char *save_cur_range_info= cur_range_info;
+  uchar *save_cur_index_tuple= dsmrr->cur_index_tuple;
+  last_identical_key_ptr= dsmrr->cur_index_tuple;
+  while (!identical_key_it.read())
+  {
+    if (DsMrr_impl::key_tuple_cmp(dsmrr, key_in_buf, dsmrr->cur_index_tuple))
+      break;
+    last_identical_key_ptr= dsmrr->cur_index_tuple;
+  }
+  identical_key_it.init(dsmrr->key_buffer);
+  dsmrr->cur_index_tuple= save_cur_index_tuple;
+  //cur_range_info= save_cur_range_info;
+  res= file->ha_index_read_map(dsmrr->table->record[0], 
+                               dsmrr->cur_index_tuple, 
+                               dsmrr->key_tuple_map, 
+                               HA_READ_KEY_EXACT);
+
+  if (res)
+  {
+    close();
+    return res; /* Fatal error */
+  }
+  get_next_row= FALSE;
+  return 0;
+}
 
-void DsMrr_impl::read_out_identical_ranges()
+
+int Key_value_records_iterator::get_next()
 {
-  if (last_identical_key_ptr)
+  handler *file= dsmrr->do_rndpos_scan? dsmrr->h2 : dsmrr->h;
+  int res;
+
+  if (get_next_row)
+  {
+    if (dsmrr->index_ranges_unique)
+      return HA_ERR_END_OF_FILE;  /* Max one match */
+
+    if ((res= file->ha_index_next_same(dsmrr->table->record[0], 
+                                       dsmrr->cur_index_tuple, 
+                                       dsmrr->key_tuple_length)))
+    {
+      /* EOF is EOF for iterator, also, any error means EOF on the iterator */
+      return res;
+    }
+    identical_key_it.init(dsmrr->key_buffer);
+  }
+
+  identical_key_it.read(); // This gets us next range_id.
+  if (!last_identical_key_ptr || (dsmrr->cur_index_tuple == last_identical_key_ptr))
   {
-    /* key_buffer.read() reads to (cur_index_tuple, cur_range_info) */
-    while (!key_buffer->read() && (cur_index_tuple != last_identical_key_ptr)) {}
-    last_identical_key_ptr= NULL;
+    get_next_row= TRUE;
   }
+  return 0;
 }
 
+void Key_value_records_iterator::close()
+{
+  while (!dsmrr->key_buffer->read() && 
+         (dsmrr->cur_index_tuple != last_identical_key_ptr)) {}
+}
 
+//////////////////////////////////////////////////////////////////////////////
+//////////////////////////////////////////////////////////////////////////////
 
 /**
   DS-MRR/CPK: multi_range_read_next() function
@@ -871,131 +940,34 @@ void DsMrr_impl::read_out_identical_ranges()
   @retval HA_ERR_END_OF_FILE  End of records
   @retval Other               Some other error
 */
-
 int DsMrr_impl::dsmrr_next_from_index(char **range_info_arg)
 {
   DBUG_ENTER("DsMrr_impl::dsmrr_next_from_index");
-  int res;
-  handler *file= do_rndpos_scan? h2: h;
+  //handler *file= do_rndpos_scan? h2: h;
 
   while (1)
   {
     bool have_record= FALSE;
-    switch (index_scan_state)
-    {
-      case GET_NEXT_IDENTICAL_KEY:
-      {
-        /* Get the next range_id for the current record */ 
-
-        /* read to (cur_index_tuple, cur_range_info) */
-        bool bres= identical_key_it->read_next();
-        DBUG_ASSERT(!bres);
-
-        if (cur_index_tuple == last_identical_key_ptr)
+    if (scanning_key_val_iter)
     {
-          /* 
-            We've just got to the last of identical ranges. Next step is to
-            go next record
-          */
-          index_scan_state= index_ranges_unique? GET_NEXT_RANGE : GET_NEXT_RECORD;
-        }
-        have_record= TRUE;
-        break;
-      }
-      case GET_NEXT_RECORD:
+      if (kv_it.get_next())
       {
-        /* Get the next record from the range */
-        res= file->ha_index_next_same(table->record[0], cur_index_tuple, 
-                                      key_tuple_length);
-        if (res)
-        {
-          if (res != HA_ERR_END_OF_FILE && res != HA_ERR_KEY_NOT_FOUND)
-            DBUG_RETURN(res);  /* Fatal error */
-
-          /* Got EOF for this range, go get the next range */
-          index_scan_state= GET_NEXT_RANGE;
-          break;
+        kv_it.close();
+        scanning_key_val_iter= FALSE;
       }
-        
+      else
         have_record= TRUE;
-        if (last_identical_key_ptr)
-        {
-          /* 
-            If the range we're scanning is one of the set of identical ranges,
-            return this record with range_id of each range
-          */
-          index_scan_state= GET_NEXT_IDENTICAL_KEY;
-          identical_key_it->init(key_buffer);
-          cur_range_info= first_identical_range_info;
-          have_record= FALSE; //psergey4
-        }
-        break;
-      }
-      case GET_NEXT_RANGE:
-      {
-        read_out_identical_ranges();
-        if (do_rndpos_scan)
-          reallocate_buffer_space();
-
-        /* Get the next range to scan */
-        if (key_buffer->read()) /* read to (cur_index_tuple,cur_range_info) */
-        {
-          index_scan_state= REFILL_KEY_BUFFER;
-          break;
-        }
-        uchar *key_in_buf= cur_index_tuple;
-
-        if (use_key_pointers)
-          cur_index_tuple= *((uchar**)cur_index_tuple);
-
-        res= file->ha_index_read_map(table->record[0], cur_index_tuple, 
-                                     key_tuple_map, HA_READ_KEY_EXACT);
-
-        if (res && res != HA_ERR_END_OF_FILE && res != HA_ERR_KEY_NOT_FOUND)
-          DBUG_RETURN(res); /* Fatal error */
-        
-        /* 
-          Check if subsequent elements in the key buffer are the same as this
-          one
-        */
-        char *save_cur_range_info= cur_range_info;
-        identical_key_it->init(key_buffer);
-        last_identical_key_ptr= NULL;
-        while (!identical_key_it->read_next())
-        {
-          if (key_tuple_cmp(this, key_in_buf, cur_index_tuple))
-            break;
-          last_identical_key_ptr= cur_index_tuple;
-        }
-        cur_range_info= save_cur_range_info;
-
-        if (last_identical_key_ptr)
-        {
-          index_scan_state= GET_NEXT_IDENTICAL_KEY;
-          identical_key_it->init(key_buffer);
-          first_identical_range_info= cur_range_info;
-          have_record= FALSE; //psergey4
     }
     else
     {
-          index_scan_state= index_ranges_unique? GET_NEXT_RANGE : GET_NEXT_RECORD;
-          have_record= TRUE;
-        }
-
-        if (res)
+      while (kv_it.init(this))
       {
-          read_out_identical_ranges();
-          index_scan_state= GET_NEXT_RANGE;
-          have_record= FALSE;
-        }
-
-        break;
-      }
-      case REFILL_KEY_BUFFER:
+        /* Failed to initialize iterator */
+        if (key_buffer->is_empty())
         {
           if (dsmrr_eof)
           {
-          index_scan_state= SCAN_FINISHED;
+            index_scan_eof= TRUE;
             DBUG_RETURN(HA_ERR_END_OF_FILE);
           }
 
@@ -1008,15 +980,13 @@ int DsMrr_impl::dsmrr_next_from_index(char **range_info_arg)
 
           if (key_buffer->is_empty())
           {
-          index_scan_state= SCAN_FINISHED;
+            index_scan_eof= TRUE;
             DBUG_RETURN(HA_ERR_END_OF_FILE);
           }
-
-        index_scan_state= GET_NEXT_RANGE;
         }
-      default:
-        DBUG_ASSERT(0);
-        break;
+      }
+      /* if we got here, it means iterator was successfully initialized */
+      scanning_key_val_iter= TRUE;
     }
 
     if (have_record &&
@@ -1035,151 +1005,6 @@ int DsMrr_impl::dsmrr_next_from_index(char **range_info_arg)
   DBUG_RETURN(0);
 }
 
-#if 0
-int DsMrr_impl::dsmrr_next_from_index(char **range_info_arg)
-{
-  int res;
-  uchar *key_in_buf;
-  handler *file= do_rndpos_scan? h2: h;
-  bool res2;
-
-  while (in_identical_keys_range)
-  {
-    /* This will read to (cur_index_tuple, cur_range_info): */
-    res2= identical_key_it->read_next();
-    DBUG_ASSERT(!res2);
-
-    if (cur_index_tuple == last_identical_key_ptr)
-    {
-      /* We're looking at the last of the identical keys */
-      in_identical_keys_range= FALSE;
-    }
-check_record:
-    if ((h->mrr_funcs.skip_index_tuple &&
-         h->mrr_funcs.skip_index_tuple(h->mrr_iter, *(char**)cur_range_info)) || 
-        (h->mrr_funcs.skip_record &&
-         h->mrr_funcs.skip_record(h->mrr_iter, *(char**)cur_range_info, NULL)))
-    {
-      continue;
-    }
-    memcpy(range_info_arg, cur_range_info, sizeof(void*));
-    return 0;
-  }
-  
-  /* Try returrning next record from the current range */
-  while (in_index_range)
-  {
-    res= file->ha_index_next_same(table->record[0], cur_index_tuple, 
-                                  key_tuple_length);
-    
-    if (res)
-    {
-      if (res != HA_ERR_END_OF_FILE && res != HA_ERR_KEY_NOT_FOUND)
-        return res;  /* Fatal error */
-
-      in_index_range= FALSE; /* no more records here */
-      break;
-    }
-    
-    if (last_identical_key_ptr)
-    {
-      in_identical_keys_range= TRUE;
-      identical_key_it->init(key_buffer);
-      cur_range_info= first_identical_range_info;
-    }
-
-    goto check_record;
-  }
-
-  while(1)
-  {
-    DBUG_ASSERT(!in_identical_keys_range && !in_index_range);
-
-    /* Jump over the keys that were handled by identical key processing */
-    if (last_identical_key_ptr)
-    {
-      /* key_buffer.read() reads to (cur_index_tuple, cur_range_info) */
-      while (!key_buffer->read() && (cur_index_tuple != last_identical_key_ptr)) {}
-      last_identical_key_ptr= NULL;
-    }
-
-    /* First, make sure we have a range at start of the buffer */
-    if (key_buffer->is_empty())
-    {
-      if (dsmrr_eof)
-      {
-        res= HA_ERR_END_OF_FILE;
-        goto end;
-      }
-      /*
-        When rowid fetching is used, it controls all buffer refills. When we're
-        on our own, try refilling our buffer.
-      */
-      if (!do_rndpos_scan)
-        dsmrr_fill_key_buffer();
-
-      if (key_buffer->is_empty())
-      {
-        res= HA_ERR_END_OF_FILE;
-        goto end;
-      }
-    }
-    
-    /*
-      At this point we're not using anything what we've read from key
-      buffer. Cut off unused key buffer space and give it to the rowid
-      buffer.
-    */
-    if (do_rndpos_scan)
-      reallocate_buffer_space();
-
-    /* Get the next range to scan */
-    key_buffer->read(); // reads to (cur_index_tuple, cur_range_info)
-    key_in_buf= cur_index_tuple;
-
-    if (use_key_pointers)
-      cur_index_tuple= *((uchar**)cur_index_tuple);
-
-    /* Do index lookup */
-    if ((res= file->ha_index_read_map(table->record[0], cur_index_tuple, 
-                                      key_tuple_map, HA_READ_KEY_EXACT)))
-    {
-      if (res != HA_ERR_END_OF_FILE && res != HA_ERR_KEY_NOT_FOUND)
-        return res;
-      continue; /* to next key and make another lookup */
-    }
-
-    /* Check if subsequent keys in the key buffer are the same as this one */
-    {
-      char *save_cur_range_info= cur_range_info;
-      identical_key_it->init(key_buffer);
-      last_identical_key_ptr= NULL;
-      while (!identical_key_it->read_next())
-      {
-        if (key_tuple_cmp(this, key_in_buf, cur_index_tuple))
-          break;
-
-        last_identical_key_ptr= cur_index_tuple;
-      }
-      cur_range_info= save_cur_range_info;
-      if (last_identical_key_ptr)
-      {
-        in_identical_keys_range= TRUE;
-        identical_key_it->init(key_buffer);
-        first_identical_range_info= cur_range_info;
-      }
-    }
-
-    in_index_range= !index_ranges_unique;
-    goto check_record;
-  }
- 
-end:
-  return res;
-}
-#endif
-
-
 /**
   DS-MRR implementation: multi_range_read_next() function.
 
@@ -1227,7 +1052,7 @@ int DsMrr_impl::dsmrr_next(char **range_info)
     {
       if (do_sort_keys)
       {
-        if (index_scan_state != SCAN_FINISHED) 
+        if (index_scan_eof) 
         {
           /* There are some sorted keys left. Use them to get rowids */
           if ((res= dsmrr_fill_rowid_buffer()))
@@ -1288,9 +1113,9 @@ int DsMrr_impl::dsmrr_next(char **range_info)
         Note: this implies that SQL layer doesn't touch table->record[0]
         between calls.
       */
-      Forward_iterator it;
+      Lifo_buffer_iterator it;
       it.init(&rowid_buffer);
-      while (!it.read_next()) // reads to (rowid, ...)
+      while (!it.read()) // reads to (rowid, ...)
       {
         if (h2->cmp_ref(rowid, cur_rowid))
           break;

sql/multi_range_read.h

@@ -48,6 +48,37 @@
 
 #include "sql_lifo_buffer.h"
 
+class DsMrr_impl;
+
+/**
+  Iterator over (record, range_id) pairs that match given key value.
+  
+  We may need to scan multiple (key_val, range_id) pairs with the same 
+  key value. A key value may have multiple matching records, so we'll need to
+  produce a cross-product of sets of matching records and range_id-s.
+*/
+
+class Key_value_records_iterator
+{
+  /* Scan parameters */
+  DsMrr_impl *dsmrr;
+  Lifo_buffer_iterator identical_key_it;
+  uchar *last_identical_key_ptr;
+  bool get_next_row;
+public:
+  /*
+  */
+  bool init(DsMrr_impl *dsmrr);
+
+  /*
+    Get next (key_val, range_id) pair.
+  */
+  int get_next();
+
+  void close();
+};
+
+
 /*
   DS-MRR implementation for one table. Create/use one object of this class for
   each ha_{myisam/innobase/etc} object. That object will be further referred to
@@ -197,17 +228,6 @@ private:
  
   /** Index scaning and key buffer-related members **/
 
-
-  enum enum_index_scan_state {
-    REFILL_KEY_BUFFER,
-    GET_NEXT_RANGE,
-    GET_NEXT_RECORD,
-    GET_NEXT_IDENTICAL_KEY,
-    SCAN_FINISHED
-  };
-
-  enum enum_index_scan_state index_scan_state;
-
   /* TRUE <=> We can get at most one index tuple for a lookup key */
   bool index_ranges_unique;
 
@@ -220,25 +240,26 @@ private:
     buffers.
   */
   Forward_lifo_buffer forward_key_buf;
-  Forward_iterator forward_key_it;
   Backward_lifo_buffer backward_key_buf;
-  Backward_iterator backward_key_it;
 
   /* Buffer to store (key, range_id) pairs */
   Lifo_buffer *key_buffer;
   
-  /* key_buffer.read() reads */
-  uchar *cur_index_tuple;
-
-  /* if in_index_range==TRUE: range_id of the range we're enumerating */
-  char *cur_range_info;
-
+  /* Index scan state */
+  bool scanning_key_val_iter;
   /* 
     TRUE <=> we've got index tuples/rowids for all keys (need this flag because 
     we may have a situation where we've read everything from the key buffer but 
     haven't finished with getting index tuples for the last key)
   */
-  //bool key_eof;
+  bool index_scan_eof;  
+  Key_value_records_iterator kv_it;
+  
+  /* key_buffer.read() reads to here */
+  uchar *cur_index_tuple;
+
+  /* if in_index_range==TRUE: range_id of the range we're enumerating */
+  char *cur_range_info;
 
   /* Initially FALSE, becomes TRUE when we've set key_tuple_xxx members */
   bool know_key_tuple_params;
@@ -255,28 +276,6 @@ private:
   /* = key_size_in_keybuf [ + sizeof(range_assoc_info) ] */
   uint key_buff_elem_size;
   
-  /* 
-    TRUE <=> we're doing key-ordered index scan and right now several
-    subsequent key values are the same as the one we've already retrieved and
-    returned index tuple for.
-  */
-  //bool in_identical_keys_range;
-
-  /* range_id of the first of the identical keys */
-  char *first_identical_range_info;
-
-  /* Pointer to the last of the identical key values */
-  uchar *last_identical_key_ptr;
-
-  /* 
-    key_buffer iterator for walking the identical key range (we need to
-    enumerate the set of (identical_key, range_id) pairs multiple times,
-    and do that by walking from current buffer read position until we get
-    last_identical_key_ptr.
-  */
-  Lifo_buffer::Iterator *identical_key_it;
-
-
   /** rnd_pos() scan and rowid buffer-related members **/
 
   /*
@@ -289,11 +288,6 @@ private:
   uchar *rowid;
   uchar *rowids_range_id;
 
-  /*
-    not-NULL: we're traversing a group of (rowid, range_id) pairs with
-              identical rowid values, and this is the pointer to the last one.
-    NULL: we're not in the group of indentical rowids.
-  */
   uchar *last_identical_rowid;
 
   bool dsmrr_eof; /* TRUE <=> We have reached EOF when reading index tuples */
@@ -315,10 +309,9 @@ private:
   void setup_buffer_sizes(key_range *sample_key);
   void reallocate_buffer_space();
   
-  void read_out_identical_ranges();
-
   static range_seq_t key_buf_seq_init(void *init_param, uint n_ranges, uint flags);
   static uint key_buf_seq_next(range_seq_t rseq, KEY_MULTI_RANGE *range);
+  friend class Key_value_records_iterator;
 };
 
 /**

sql/sql_lifo_buffer.h

@@ -112,40 +112,17 @@ public:
   virtual void reset() = 0;
   virtual uchar *end_of_space() = 0;
 protected:
-  bool have_data(size_t bytes)
-  {
-    return (used_size() >= bytes);
-  }
   virtual bool have_space_for(size_t bytes) = 0;
   virtual size_t used_size() = 0;
   
+  /* To be used only by iterator class: */
+  virtual uchar *get_pos()= 0;
+  virtual bool read(uchar **position)= 0;
+  friend class Lifo_buffer_iterator;
 public:
-
   virtual void remove_unused_space(uchar **unused_start, uchar **unused_end)=0;
   virtual uchar *used_area() = 0; 
-   
-  /** Iterator to walk over contents of the buffer without reading it. */
-  class Iterator
-  {
-  public:
-    virtual void init(Lifo_buffer *buf) = 0;
-    /*
-      Read the next value. The calling convention is the same as buf->read()
-      has.
-
-      @retval FALSE - ok
-      @retval TRUE  - EOF, reached the end of the buffer
-    */
-    virtual bool read_next()= 0;
-    virtual ~Iterator() {}
-  protected:
-    Lifo_buffer *buf;
-    virtual uchar *get_next(size_t nbytes)=0;
-  };
   virtual ~Lifo_buffer() {};
-
-  friend class Forward_iterator;
-  friend class Backward_iterator;
 };
 
 
@@ -196,19 +173,24 @@ public:
     memcpy(pos, data, bytes);
     pos += bytes;
   }
-  uchar *read_bytes(size_t bytes)
+  bool have_data(uchar *position, size_t bytes)
   {
-    DBUG_ASSERT(have_data(bytes));
-    pos= pos - bytes;
-    return pos;
+    return ((position - start) >= (ptrdiff_t)bytes);
   }
-  bool read()
+  uchar *read_bytes(uchar **position, size_t bytes)
+  {
+    DBUG_ASSERT(have_data(*position, bytes));
+    *position= (*position) - bytes;
+    return *position;
+  }
+  bool read() { return read(&pos); }
+  bool read(uchar **position)
   {
-    if (!have_data(size1 + (read_ptr2 ? size2 : 0)))
+    if (!have_data(*position, size1 + (read_ptr2 ? size2 : 0)))
       return TRUE;
     if (read_ptr2)
-      *read_ptr2= read_bytes(size2);
-    *read_ptr1= read_bytes(size1);
+      *read_ptr2= read_bytes(position, size2);
+    *read_ptr1= read_bytes(position, size1);
     return FALSE;
   }
   void remove_unused_space(uchar **unused_start, uchar **unused_end)
@@ -231,58 +213,11 @@ public:
   }
   /* Return pointer to start of the memory area that is occupied by the data */
   uchar *used_area() { return start; }
-  friend class Forward_iterator;
+  friend class Lifo_buffer_iterator;
+  uchar *get_pos() { return pos; }
 };
 
 
-/**
-  Iterator for Forward_lifo_buffer
-*/
-
-class Forward_iterator : public Lifo_buffer::Iterator
-{
-  uchar *pos;
-
-  /** Return pointer to next chunk of nbytes bytes and avance over it */
-  uchar *get_next(size_t nbytes)
-  {
-    if (pos - nbytes < ((Forward_lifo_buffer*)buf)->start)
-      return NULL;
-    pos -= nbytes;
-    return pos;
-  }
-public:
-  bool read_next()
-  {
-    uchar *res;
-    if (buf->read_ptr2)
-    {
-      if ((res= get_next(buf->size2)))
-      {
-        *(buf->read_ptr2)= res;
-        *buf->read_ptr1= get_next(buf->size1);
-        return FALSE;
-      }
-    }
-    else
-    {
-      if ((res= get_next(buf->size1)))
-      {
-        *(buf->read_ptr1)= res;
-        return FALSE;
-      }
-    }
-    return TRUE; /* EOF */
-  }
-
-  void init(Lifo_buffer *buf_arg)
-  {
-    DBUG_ASSERT(buf_arg->type() == Lifo_buffer::FORWARD);
-    buf= buf_arg;
-    pos= ((Forward_lifo_buffer*)buf)->pos;
-  }
-};
-
 
 /**
   Backward LIFO buffer
@@ -332,18 +267,26 @@ public:
   }
   bool read()
   {
-    if (!have_data(size1 + (read_ptr2 ? size2 : 0)))
+    return read(&pos);
+  }
+  bool read(uchar **position)
+  {
+    if (!have_data(*position, size1 + (read_ptr2 ? size2 : 0)))
       return TRUE;
-    *read_ptr1= read_bytes(size1);
+    *read_ptr1= read_bytes(position, size1);
     if (read_ptr2)
-      *read_ptr2= read_bytes(size2);
+      *read_ptr2= read_bytes(position, size2);
     return FALSE;
   }
-  uchar *read_bytes(size_t bytes)
+  bool have_data(uchar *position, size_t bytes)
+  {
+    return ((end - position) >= (ptrdiff_t)bytes);
+  }
+  uchar *read_bytes(uchar **position, size_t bytes)
   {
-    DBUG_ASSERT(have_data(bytes));
-    uchar *ret= pos;
-    pos= pos + bytes;
+    DBUG_ASSERT(have_data(*position, bytes));
+    uchar *ret= *position;
+    *position= *position + bytes;
     return ret;
   }
   /**
@@ -363,50 +306,34 @@ public:
   }
   /* Return pointer to start of the memory area that is occupied by the data */
   uchar *used_area() { return pos; }
-  friend class Backward_iterator;
+  friend class Lifo_buffer_iterator;
+  uchar *get_pos() { return pos; }
 };
 
 
-/**
-  Iterator for Backward_lifo_buffer
-*/
 
-class Backward_iterator : public Lifo_buffer::Iterator
+/** Iterator to walk over contents of the buffer without reading it. */
+class Lifo_buffer_iterator
 {
   uchar *pos;
-  /* Return pointer to next chunk of nbytes bytes and advance over it */
-  uchar *get_next(size_t nbytes)
-  {
-    if (pos + nbytes > ((Backward_lifo_buffer*)buf)->end)
-      return NULL;
-    uchar *res= pos;
-    pos += nbytes;
-    return res;
-  }
+  Lifo_buffer *buf;
 public:
-  bool read_next()
+  void init(Lifo_buffer *buf_arg)
   {
+    buf= buf_arg;
+    pos= buf->get_pos();
+  }
   /*
-      Always read the first component first (if the buffer is backwards, we
-      have written the second component first).
+    Read the next value. The calling convention is the same as buf->read()
+    has.
+
+    @retval FALSE - ok
+    @retval TRUE  - EOF, reached the end of the buffer
   */
-    uchar *res;
-    if ((res= get_next(buf->size1)))
-    {
-      *(buf->read_ptr1)= res;
-      if (buf->read_ptr2)
-        *buf->read_ptr2= get_next(buf->size2);
-      return FALSE;
-    }
-    return TRUE; /* EOF */
-  }
-  void init(Lifo_buffer *buf_arg)
+  bool read() 
   {
-    DBUG_ASSERT(buf_arg->type() == Lifo_buffer::BACKWARD);
-    buf= buf_arg;
-    pos= ((Backward_lifo_buffer*)buf)->pos;
+    return buf->read(&pos);
   }
 };
 
 
-