documenting HA_STATUS_xxx flags

include/my_base.h

@@ -260,14 +260,47 @@ enum ha_base_keytype {
 #define HA_CREATE_CHECKSUM	8
 #define HA_CREATE_DELAY_KEY_WRITE 64
 
-	/* Bits in flag to _status */
+/*
+  The following flags (OR-ed) are passed to handler::info() method.
+  The method copies misc handler information out of the storage engine
+  to data structures accessible from MySQL
 
-#define HA_STATUS_POS		1		/* Return position */
-#define HA_STATUS_NO_LOCK	2		/* Don't use external lock */
-#define HA_STATUS_TIME		4		/* Return update time */
-#define HA_STATUS_CONST		8		/* Return constants values */
+  Same flags are also passed down to mi_status, myrg_status, etc.
+*/
+
+/* this one is not used */
+#define HA_STATUS_POS            1
+/*
+  assuming the table keeps shared actual copy of the 'info' and
+  local, possibly outdated copy, the following flag means that
+  it should not try to get the actual data (locking the shared structure)
+  slightly outdated version will suffice
+*/
+#define HA_STATUS_NO_LOCK        2
+/* update the time of the last modification (in handler::update_time) */
+#define HA_STATUS_TIME           4
+/*
+  update the 'constant' part of the info:
+  handler::max_data_file_length, max_index_file_length, create_time
+  sortkey, ref_length, block_size, data_file_name, index_file_name.
+  handler::table->s->keys_in_use, keys_for_keyread, rec_per_key
+*/
+#define HA_STATUS_CONST          8
+/*
+  update the 'variable' part of the info:
+  handler::records, deleted, data_file_length, index_file_length,
+  delete_length, check_time, mean_rec_length
+*/
 #define HA_STATUS_VARIABLE      16
+/*
+  get the information about the key that caused last duplicate value error
+  update handler::errkey and handler::dupp_ref
+  see handler::get_dup_key()
+*/
 #define HA_STATUS_ERRKEY        32
+/*
+  update handler::auto_increment_value
+*/
 #define HA_STATUS_AUTO          64
 
 	/* Errorcodes given by functions */

sql/examples/ha_example.cc

@@ -480,6 +480,8 @@ int ha_example::rnd_pos(byte * buf, byte *pos)
 
 /*
   ::info() is used to return information to the optimizer.
+  see my_base.h for the complete description
+
   Currently this table handler doesn't implement most of the fields
   really needed. SHOW also makes use of this data
   Another note, you will probably want to have the following in your

sql/handler.h

@@ -672,7 +672,7 @@ public:
                                    key_range *max_key)
     { return (ha_rows) 10; }
   virtual void position(const byte *record)=0;
-  virtual void info(uint)=0;
+  virtual void info(uint)=0; // see my_base.h for full description
   virtual int extra(enum ha_extra_function operation)
   { return 0; }
   virtual int extra_opt(enum ha_extra_function operation, ulong cache_size)