Additional storage engine called "blackhole". Customer request, and for that matter a Zawodny request. With this you can alter table to a type of table that would never store data. Its a /dev/null for a database.

sql/Makefile.am

@@ -60,7 +60,7 @@ noinst_HEADERS =	item.h item_func.h item_sum.h item_cmpfunc.h \
 			stacktrace.h sql_sort.h sql_cache.h set_var.h \
 			spatial.h gstream.h client_settings.h tzfile.h \
                         tztime.h examples/ha_example.h examples/ha_archive.h \
-			examples/ha_tina.h
+			examples/ha_tina.h ha_blackhole.h
 mysqld_SOURCES =	sql_lex.cc sql_handler.cc \
 			item.cc item_sum.cc item_buff.cc item_func.cc \
 			item_cmpfunc.cc item_strfunc.cc item_timefunc.cc \
@@ -92,7 +92,7 @@ mysqld_SOURCES =	sql_lex.cc sql_handler.cc \
 			gstream.cc spatial.cc sql_help.cc protocol_cursor.cc \
 			tztime.cc my_time.c \
 			examples/ha_example.cc examples/ha_archive.cc \
-			examples/ha_tina.cc
+			examples/ha_tina.cc ha_blackhole.cc
 
 gen_lex_hash_SOURCES =	gen_lex_hash.cc
 gen_lex_hash_LDADD =	$(LDADD) $(CXXLDFLAGS)

sql/ha_blackhole.cc

@@ -0,0 +1,164 @@
+/* Copyright (C) 2005 MySQL AB
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+
+#ifdef __GNUC__
+#pragma implementation        // gcc: Class implementation
+#endif
+
+#include <mysql_priv.h>
+
+#ifdef HAVE_BLACKHOLE_DB
+#include "ha_blackhole.h"
+
+
+const char **ha_blackhole::bas_ext() const
+{ 
+  static const char *ext[]= { NullS }; 
+  return ext; 
+}
+
+int ha_blackhole::open(const char *name, int mode, uint test_if_locked)
+{
+  DBUG_ENTER("ha_blackhole::open");
+  thr_lock_init(&thr_lock);
+  thr_lock_data_init(&thr_lock,&lock,NULL);
+  DBUG_RETURN(0);
+}
+
+int ha_blackhole::close(void)
+{
+  DBUG_ENTER("ha_blackhole::close");
+  thr_lock_delete(&thr_lock);
+  DBUG_RETURN(0);
+}
+
+int ha_blackhole::create(const char *name, TABLE *table_arg,
+                       HA_CREATE_INFO *create_info)
+{
+  DBUG_ENTER("ha_blackhole::create");
+  DBUG_RETURN(0);
+}
+
+const char *ha_blackhole::index_type(uint key_number)
+{
+  DBUG_ENTER("ha_blackhole::index_type");
+  DBUG_RETURN((table->key_info[key_number].flags & HA_FULLTEXT) ? 
+	  "FULLTEXT" :
+	  (table->key_info[key_number].flags & HA_SPATIAL) ?
+	  "SPATIAL" :
+	  (table->key_info[key_number].algorithm == HA_KEY_ALG_RTREE) ?
+	  "RTREE" :
+	  "BTREE");
+}
+
+int ha_blackhole::write_row(byte * buf)
+{
+  DBUG_ENTER("ha_blackhole::write_row");
+  DBUG_RETURN(0);
+}
+
+int ha_blackhole::rnd_init(bool scan)
+{
+  DBUG_ENTER("ha_blackhole::rnd_init");
+  DBUG_RETURN(0);
+}
+
+
+int ha_blackhole::rnd_next(byte *buf)
+{
+  DBUG_ENTER("ha_blackhole::rnd_next");
+  DBUG_RETURN(HA_ERR_END_OF_FILE);
+}
+
+
+int ha_blackhole::rnd_pos(byte * buf, byte *pos)
+{
+  DBUG_ENTER("ha_blackhole::rnd_pos");
+  DBUG_RETURN(0);
+}
+
+
+void ha_blackhole::position(const byte *record)
+{
+  DBUG_ENTER("ha_blackhole::position");
+  DBUG_VOID_RETURN;
+}
+
+
+void ha_blackhole::info(uint flag)
+{
+  DBUG_ENTER("ha_blackhole::info");
+
+  records= 0;
+  deleted= 0;
+  errkey= 0;
+  mean_rec_length= 0;
+  data_file_length= 0;
+  index_file_length= 0;
+  max_data_file_length= 0;
+  delete_length= 0;
+  if (flag & HA_STATUS_AUTO)
+    auto_increment_value= 1;
+  DBUG_VOID_RETURN;
+}
+
+int ha_blackhole::external_lock(THD *thd, int lock_type)
+{
+  DBUG_ENTER("ha_blackhole::external_lock");
+  DBUG_RETURN(0);
+}
+
+
+THR_LOCK_DATA **ha_blackhole::store_lock(THD *thd,
+                                       THR_LOCK_DATA **to,
+                                       enum thr_lock_type lock_type)
+{
+  if (lock_type != TL_IGNORE && lock.type == TL_UNLOCK) 
+  {
+    /* 
+      Here is where we get into the guts of a row level lock.
+      If TL_UNLOCK is set 
+      If we are not doing a LOCK TABLE or DISCARD/IMPORT
+      TABLESPACE, then allow multiple writers 
+    */
+
+    if ((lock_type >= TL_WRITE_CONCURRENT_INSERT &&
+         lock_type <= TL_WRITE) && !thd->in_lock_tables
+        && !thd->tablespace_op)
+      lock_type = TL_WRITE_ALLOW_WRITE;
+
+    /* 
+      In queries of type INSERT INTO t1 SELECT ... FROM t2 ...
+      MySQL would use the lock TL_READ_NO_INSERT on t2, and that
+      would conflict with TL_WRITE_ALLOW_WRITE, blocking all inserts
+      to t2. Convert the lock to a normal read lock to allow
+      concurrent inserts to t2. 
+    */
+
+    if (lock_type == TL_READ_NO_INSERT && !thd->in_lock_tables) 
+      lock_type = TL_READ;
+
+    lock.type=lock_type;
+  }
+
+  *to++= &lock;
+
+  return to;
+}
+
+
+#endif /* HAVE_BLACKHOLE_DB */

sql/ha_blackhole.h

@@ -0,0 +1,79 @@
+/* Copyright (C) 2005 MySQL AB
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+#ifdef __GNUC__
+#pragma interface			/* gcc class implementation */
+#endif
+
+/*
+  Class definition for the blackhole storage engine
+  "Dumbest named feature ever"
+*/
+class ha_blackhole: public handler
+{
+  THR_LOCK_DATA lock;      /* MySQL lock */
+  THR_LOCK thr_lock;
+
+public:
+  ha_blackhole(TABLE *table): handler(table)
+  {
+  }
+  ~ha_blackhole()
+  {
+  }
+  /* The name that will be used for display purposes */
+  const char *table_type() const { return "BLACKHOLE"; }
+  /*
+    The name of the index type that will be used for display
+    don't implement this method unless you really have indexes
+   */
+  const char *index_type(uint key_number);
+  const char **bas_ext() const;
+  ulong table_flags() const
+  {
+    return(HA_NULL_IN_KEY | HA_CAN_FULLTEXT | HA_CAN_SQL_HANDLER |
+           HA_DUPP_POS | HA_CAN_INDEX_BLOBS | HA_AUTO_PART_KEY |
+           HA_FILE_BASED | HA_CAN_GEOMETRY | HA_READ_RND_SAME |
+           HA_CAN_INSERT_DELAYED);
+  }
+  ulong index_flags(uint inx, uint part, bool all_parts) const
+  {
+    return ((table->key_info[inx].algorithm == HA_KEY_ALG_FULLTEXT) ?
+            0 : HA_READ_NEXT | HA_READ_PREV | HA_READ_RANGE |
+            HA_READ_ORDER | HA_KEYREAD_ONLY);
+  }
+  /* The following defines can be increased if necessary */
+#define BLACKHOLE_MAX_KEY	64		/* Max allowed keys */
+#define BLACKHOLE_MAX_KEY_SEG	16		/* Max segments for key */
+#define BLACKHOLE_MAX_KEY_LENGTH 1000
+  uint max_supported_keys()          const { return BLACKHOLE_MAX_KEY; }
+  uint max_supported_key_length()    const { return BLACKHOLE_MAX_KEY_LENGTH; }
+  uint max_supported_key_part_length() const { return BLACKHOLE_MAX_KEY_LENGTH; }
+  int open(const char *name, int mode, uint test_if_locked);
+  int close(void);
+  int write_row(byte * buf);
+  int rnd_init(bool scan);
+  int rnd_next(byte *buf);
+  int rnd_pos(byte * buf, byte *pos);
+  void position(const byte *record);
+  void info(uint flag);
+  int external_lock(THD *thd, int lock_type);
+  int create(const char *name, TABLE *table_arg,
+                           HA_CREATE_INFO *create_info);
+  THR_LOCK_DATA **store_lock(THD *thd,
+                                           THR_LOCK_DATA **to,
+                                           enum thr_lock_type lock_type);
+};

sql/handler.cc

@@ -32,6 +32,9 @@
 #ifdef HAVE_BERKELEY_DB
 #include "ha_berkeley.h"
 #endif
+#ifdef HAVE_BLACKHOLE_DB
+#include "ha_blackhole.h"
+#endif
 #ifdef HAVE_EXAMPLE_DB
 #include "examples/ha_example.h"
 #endif
@@ -96,6 +99,8 @@ struct show_table_type_st sys_table_types[]=
    "Archive storage engine", DB_TYPE_ARCHIVE_DB},
   {"CSV",&have_csv_db,
    "CSV storage engine", DB_TYPE_CSV_DB},
+  {"BLACKHOLE",&have_blackhole_db,
+   "Storage engine designed to act as null storage", DB_TYPE_BLACKHOLE_DB},
   {NullS, NULL, NullS, DB_TYPE_UNKNOWN}
 };
 
@@ -204,6 +209,10 @@ handler *get_new_handler(TABLE *table, enum db_type db_type)
   case DB_TYPE_ARCHIVE_DB:
     return new ha_archive(table);
 #endif
+#ifdef HAVE_BLACKHOLE_DB
+  case DB_TYPE_BLACKHOLE_DB:
+    return new ha_blackhole(table);
+#endif
 #ifdef HAVE_CSV_DB
   case DB_TYPE_CSV_DB:
     return new ha_tina(table);

sql/handler.h

@@ -150,6 +150,7 @@ enum db_type
   DB_TYPE_BERKELEY_DB, DB_TYPE_INNODB, 
   DB_TYPE_GEMINI, DB_TYPE_NDBCLUSTER,
   DB_TYPE_EXAMPLE_DB, DB_TYPE_ARCHIVE_DB, DB_TYPE_CSV_DB,
+  DB_TYPE_BLACKHOLE_DB,
 	       
   DB_TYPE_DEFAULT // Must be last
 };

sql/mysql_priv.h

@@ -967,6 +967,7 @@ extern SHOW_COMP_OPTION have_query_cache, have_berkeley_db, have_innodb;
 extern SHOW_COMP_OPTION have_geometry, have_rtree_keys;
 extern SHOW_COMP_OPTION have_crypt;
 extern SHOW_COMP_OPTION have_compress;
+extern SHOW_COMP_OPTION have_blackhole_db;
 
 #ifndef __WIN__
 extern pthread_t signal_thread;

sql/mysqld.cc

@@ -398,6 +398,7 @@ SHOW_COMP_OPTION have_berkeley_db, have_innodb, have_isam, have_ndbcluster,
 SHOW_COMP_OPTION have_raid, have_openssl, have_symlink, have_query_cache;
 SHOW_COMP_OPTION have_geometry, have_rtree_keys;
 SHOW_COMP_OPTION have_crypt, have_compress;
+SHOW_COMP_OPTION have_blackhole_db;
 
 /* Thread specific variables */
 
@@ -5758,6 +5759,11 @@ static void mysql_init_variables(void)
 #else
   have_archive_db= SHOW_OPTION_NO;
 #endif
+#ifdef HAVE_BLACKHOLE_DB
+  have_blackhole_db= SHOW_OPTION_YES;
+#else
+  have_blackhole_db= SHOW_OPTION_NO;
+#endif
 #ifdef HAVE_CSV_DB
   have_csv_db= SHOW_OPTION_YES;
 #else

sql/set_var.cc

@@ -703,6 +703,7 @@ struct show_var_st init_vars[]= {
   {sys_group_concat_max_len.name, (char*) &sys_group_concat_max_len,  SHOW_SYS},
   {"have_archive",	      (char*) &have_archive_db,	            SHOW_HAVE},
   {"have_bdb",		      (char*) &have_berkeley_db,	    SHOW_HAVE},
+  {"have_blackhole_engine",   (char*) &have_blackhole_db,	    SHOW_HAVE},
   {"have_compress",	      (char*) &have_compress,		    SHOW_HAVE},
   {"have_crypt",	      (char*) &have_crypt,		    SHOW_HAVE},
   {"have_csv",	              (char*) &have_csv_db,	            SHOW_HAVE},