MWL#182: Explain running statements

First code
- "Asynchronous procedure call" system
- new THD::check_killed() that serves APC request is called from within most important loops
- EXPLAIN code is now able to generate EXPLAIN output on-the-fly [incomplete]

Parts that are still missing:
- put THD::check_killed() call into every loop where we could spend significant amount of time
- Make sure EXPLAIN code works for group-by queries that replace JOIN::join_tab with make_simple_join() 
  and other such cases.
- User interface: what error code to use, where to get timeout settings from, etc.

1 files changed, 19 insertions, 0 deletions

diff --git a/sql/protocol.h b/sql/protocol.h
index e07af5208db..7a882e8a10d 100644
--- a/sql/protocol.h
+++ b/sql/protocol.h
@@ -28,6 +28,7 @@ class Protocol
 protected:
   THD	 *thd;
   String *packet;
+  /* Used by net_store_data() for charset conversions */
   String *convert;
   uint field_pos;
 #ifndef DBUG_OFF
@@ -42,6 +43,10 @@ protected:
   MYSQL_FIELD *next_mysql_field;
   MEM_ROOT *alloc;
 #endif
+  /* 
+    The following two are low-level functions that are invoked from
+    higher-level store_xxx() funcs.  The data is stored into this->packet.
+  */
   bool net_store_data(const uchar *from, size_t length,
                       CHARSET_INFO *fromcs, CHARSET_INFO *tocs);
   bool store_string_aux(const char *from, size_t length,
@@ -55,6 +60,20 @@ public:
   enum { SEND_NUM_ROWS= 1, SEND_DEFAULTS= 2, SEND_EOF= 4 };
   virtual bool send_fields(List<Item> *list, uint flags);
 
+  void get_packet(const char **start, size_t *length) 
+  {
+    *start= packet->ptr();
+    *length= packet->length(); 
+  }
+  void set_packet(const char *start, size_t len)
+  {
+    packet->length(0);
+    packet->append(start, len);
+#ifndef DBUG_OFF
+  field_pos= field_count - 1;
+#endif
+  }
+
   bool store(I_List<i_string> *str_list);
   bool store(const char *from, CHARSET_INFO *cs);
   String *storage_packet() { return packet; }