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5f911fa874
Bug#54678: InnoDB, TRUNCATE, ALTER, I_S SELECT, crash or deadlock - Incompatible change: truncate no longer resorts to a row by row delete if the storage engine does not support the truncate method. Consequently, the count of affected rows does not, in any case, reflect the actual number of rows. - Incompatible change: it is no longer possible to truncate a table that participates as a parent in a foreign key constraint, unless it is a self-referencing constraint (both parent and child are in the same table). To work around this incompatible change and still be able to truncate such tables, disable foreign checks with SET foreign_key_checks=0 before truncate. Alternatively, if foreign key checks are necessary, please use a DELETE statement without a WHERE condition. Problem description: The problem was that for storage engines that do not support truncate table via a external drop and recreate, such as InnoDB which implements truncate via a internal drop and recreate, the delete_all_rows method could be invoked with a shared metadata lock, causing problems if the engine needed exclusive access to some internal metadata. This problem originated with the fact that there is no truncate specific handler method, which ended up leading to a abuse of the delete_all_rows method that is primarily used for delete operations without a condition. Solution: The solution is to introduce a truncate handler method that is invoked when the engine does not support truncation via a table drop and recreate. This method is invoked under a exclusive metadata lock, so that there is only a single instance of the table when the method is invoked. Also, the method is not invoked and a error is thrown if the table is a parent in a non-self-referencing foreign key relationship. This was necessary to avoid inconsistency as some integrity checks are bypassed. This is inline with the fact that truncate is primarily a DDL operation that was designed to quickly remove all data from a table.
105 lines
3.9 KiB
C++
105 lines
3.9 KiB
C++
/* Copyright 2005-2008 MySQL AB, 2008 Sun Microsystems, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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#ifdef USE_PRAGMA_INTERFACE
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#pragma interface /* gcc class implementation */
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#endif
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#include "thr_lock.h" /* THR_LOCK */
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#include "handler.h" /* handler */
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#include "table.h" /* TABLE_SHARE */
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/*
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Shared structure for correct LOCK operation
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*/
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struct st_blackhole_share {
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THR_LOCK lock;
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uint use_count;
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uint table_name_length;
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char table_name[1];
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};
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/*
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Class definition for the blackhole storage engine
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"Dumbest named feature ever"
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*/
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class ha_blackhole: public handler
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{
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THR_LOCK_DATA lock; /* MySQL lock */
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st_blackhole_share *share;
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public:
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ha_blackhole(handlerton *hton, TABLE_SHARE *table_arg);
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~ha_blackhole()
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{
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}
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/* The name that will be used for display purposes */
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const char *table_type() const { return "BLACKHOLE"; }
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/*
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The name of the index type that will be used for display
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don't implement this method unless you really have indexes
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*/
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const char *index_type(uint key_number);
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const char **bas_ext() const;
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ulonglong table_flags() const
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{
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return(HA_NULL_IN_KEY | HA_CAN_FULLTEXT | HA_CAN_SQL_HANDLER |
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HA_BINLOG_STMT_CAPABLE | HA_BINLOG_ROW_CAPABLE |
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HA_CAN_INDEX_BLOBS | HA_AUTO_PART_KEY |
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HA_FILE_BASED | HA_CAN_GEOMETRY | HA_CAN_INSERT_DELAYED);
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}
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ulong index_flags(uint inx, uint part, bool all_parts) const
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{
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return ((table_share->key_info[inx].algorithm == HA_KEY_ALG_FULLTEXT) ?
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0 : HA_READ_NEXT | HA_READ_PREV | HA_READ_RANGE |
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HA_READ_ORDER | HA_KEYREAD_ONLY);
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}
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/* The following defines can be increased if necessary */
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#define BLACKHOLE_MAX_KEY 64 /* Max allowed keys */
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#define BLACKHOLE_MAX_KEY_SEG 16 /* Max segments for key */
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#define BLACKHOLE_MAX_KEY_LENGTH 1000
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uint max_supported_keys() const { return BLACKHOLE_MAX_KEY; }
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uint max_supported_key_length() const { return BLACKHOLE_MAX_KEY_LENGTH; }
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uint max_supported_key_part_length() const { return BLACKHOLE_MAX_KEY_LENGTH; }
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int open(const char *name, int mode, uint test_if_locked);
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int close(void);
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int truncate();
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int rnd_init(bool scan);
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int rnd_next(uchar *buf);
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int rnd_pos(uchar * buf, uchar *pos);
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int index_read_map(uchar * buf, const uchar * key, key_part_map keypart_map,
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enum ha_rkey_function find_flag);
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int index_read_idx_map(uchar * buf, uint idx, const uchar * key,
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key_part_map keypart_map,
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enum ha_rkey_function find_flag);
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int index_read_last_map(uchar * buf, const uchar * key, key_part_map keypart_map);
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int index_next(uchar * buf);
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int index_prev(uchar * buf);
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int index_first(uchar * buf);
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int index_last(uchar * buf);
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void position(const uchar *record);
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int info(uint flag);
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int external_lock(THD *thd, int lock_type);
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int create(const char *name, TABLE *table_arg,
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HA_CREATE_INFO *create_info);
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THR_LOCK_DATA **store_lock(THD *thd,
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THR_LOCK_DATA **to,
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enum thr_lock_type lock_type);
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private:
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virtual int write_row(uchar *buf);
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virtual int update_row(const uchar *old_data, uchar *new_data);
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virtual int delete_row(const uchar *buf);
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};
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