[Commits] 21a15ea673c: MDEV-16240: Assertion `0' failed in row_sel_convert_mysql_key_to_innobase
revision-id: 21a15ea673c9cda1635ce06391b9f56d7a461186 (mariadb-10.2.22-72-g21a15ea673c) parent(s): bb8c82c66abddf796e8d44f817518e5ab38ae6e4 author: Oleksandr Byelkin committer: Oleksandr Byelkin timestamp: 2019-03-14 15:12:47 +0100 message: MDEV-16240: Assertion `0' failed in row_sel_convert_mysql_key_to_innobase Set table in row ID position mode before using this function. --- mysql-test/r/multi_update_innodb.result | 40 +++++++++++++++++++++ mysql-test/t/multi_update_innodb.test | 49 +++++++++++++++++++++++++ sql/handler.cc | 11 ++++-- sql/item_subselect.cc | 10 ++++-- sql/item_subselect.h | 2 +- sql/log_event.cc | 9 +++++ sql/sql_insert.cc | 64 +++++++++++++++++++++++++++------ sql/sql_load.cc | 10 ++++++ sql/sql_select.cc | 10 ++++++ sql/sql_update.cc | 4 +++ 10 files changed, 193 insertions(+), 16 deletions(-) diff --git a/mysql-test/r/multi_update_innodb.result b/mysql-test/r/multi_update_innodb.result index 5890fd24f5f..294ebfcebdf 100644 --- a/mysql-test/r/multi_update_innodb.result +++ b/mysql-test/r/multi_update_innodb.result @@ -151,3 +151,43 @@ create table t2 like t1; insert into t2 select * from t1; delete t1,t2 from t2,t1 where t1.a<'B' and t2.b=t1.b; drop table t1,t2; +# +# MDEV-16240: Assertion `0' failed in +# row_sel_convert_mysql_key_to_innobase +# +SET @save_sql_mode=@@sql_mode; +set sql_mode=''; +CREATE TABLE `t3` ( +`f1` TIMESTAMP NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE current_timestamp(), +`f2` datetime DEFAULT '2000-01-01 00:00:00' ON UPDATE current_timestamp(), +`f3` TIMESTAMP NULL DEFAULT '2000-01-01 00:00:00', +`pk` datetime NOT NULL DEFAULT '0000-00-00 00:00:00', +`f4` datetime DEFAULT current_timestamp(), +PRIMARY KEY (`pk`), +UNIQUE KEY `f2k` (`f2`), +KEY `f4k` (`f4`) +) ENGINE=InnoDB; +INSERT INTO `t3` VALUES ('2018-05-18 15:08:07','2018-05-18 17:08:07','0000-00-00 00:00:00','0000-00-00 00:00:00','0000-00-00 00:00:00'),('0000-00-00 00:00:00','0000-00-00 00:00:00','1999-12-31 23:00:00','2002-07-03 23:04:40','0000-00-00 00:00:00'); +CREATE VIEW `v1` AS +SELECT `t3`.`pk` AS `pk`, +`t3`.`f3` AS `f3`, +`t3`.`f4` AS `f4`, +`t3`.`f2` AS `f2`, +`t3`.`f1` AS `f1` +FROM `t3`; +CREATE TABLE `t4` ( +`f1` datetime DEFAULT current_timestamp() ON UPDATE current_timestamp(), +`f3` timestamp NULL DEFAULT NULL, +`f2` timestamp NULL DEFAULT '1999-12-31 23:00:00' ON UPDATE current_timestamp(), +`pk` int(11) NOT NULL, +`f4` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(), +PRIMARY KEY (`pk`) +) ENGINE=InnoDB; +INSERT INTO `t4` VALUES ('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,1,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,3,'2018-05-18 15:08:06'),('0000-00-00 00:00:00','0000-00-00 00:00:00',NULL,1976,'0000-00-00 00:00:00'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2000,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2001,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2002,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2003,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2004,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','2018-05-18 15:08:06',2005,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','2018-05-18 15:08:06',2018,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','2018-05-18 15:08:06',2019,'2018-05-1 8 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','2018-05-18 15:08:06',2024,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','1999-12-31 23:00:00',2025,'2018-05-18 15:08:06'),('0000-00-00 00:00:00',NULL,'2018-05-18 15:08:06',2026,'2018-05-18 15:08:06'),('2018-05-18 17:08:07','0000-00-00 00:00:00','0000-00-00 00:00:00',2027,'0000-00-00 00:00:00'); +UPDATE `v1` t1, `t4` t2 +SET t1.`f2` = 6452736 WHERE t1.`f4` = 6272000; +ERROR 23000: Duplicate entry '0000-00-00 00:00:00' for key 'f2k' +DROP VIEW v1; +DROP TABLE t3,t4; +SET @@sql_mode=@save_sql_mode; +# End of 10.2 tests diff --git a/mysql-test/t/multi_update_innodb.test b/mysql-test/t/multi_update_innodb.test index f5f8f91edb8..2e46ee06d4d 100644 --- a/mysql-test/t/multi_update_innodb.test +++ b/mysql-test/t/multi_update_innodb.test @@ -173,3 +173,52 @@ delete t1,t2 from t2,t1 where t1.a<'B' and t2.b=t1.b; drop table t1,t2; +--echo # +--echo # MDEV-16240: Assertion `0' failed in +--echo # row_sel_convert_mysql_key_to_innobase +--echo # + +SET @save_sql_mode=@@sql_mode; +set sql_mode=''; + +CREATE TABLE `t3` ( + `f1` TIMESTAMP NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE current_timestamp(), + `f2` datetime DEFAULT '2000-01-01 00:00:00' ON UPDATE current_timestamp(), + `f3` TIMESTAMP NULL DEFAULT '2000-01-01 00:00:00', + `pk` datetime NOT NULL DEFAULT '0000-00-00 00:00:00', + `f4` datetime DEFAULT current_timestamp(), + PRIMARY KEY (`pk`), + UNIQUE KEY `f2k` (`f2`), + KEY `f4k` (`f4`) + ) ENGINE=InnoDB; + +INSERT INTO `t3` VALUES ('2018-05-18 15:08:07','2018-05-18 17:08:07','0000-00-00 00:00:00','0000-00-00 00:00:00','0000-00-00 00:00:00'),('0000-00-00 00:00:00','0000-00-00 00:00:00','1999-12-31 23:00:00','2002-07-03 23:04:40','0000-00-00 00:00:00'); + +CREATE VIEW `v1` AS +SELECT `t3`.`pk` AS `pk`, + `t3`.`f3` AS `f3`, + `t3`.`f4` AS `f4`, + `t3`.`f2` AS `f2`, + `t3`.`f1` AS `f1` +FROM `t3`; + +CREATE TABLE `t4` ( + `f1` datetime DEFAULT current_timestamp() ON UPDATE current_timestamp(), + `f3` timestamp NULL DEFAULT NULL, + `f2` timestamp NULL DEFAULT '1999-12-31 23:00:00' ON UPDATE current_timestamp(), + `pk` int(11) NOT NULL, + `f4` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(), + PRIMARY KEY (`pk`) +) ENGINE=InnoDB; + +INSERT INTO `t4` VALUES ('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,1,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,3,'2018-05-18 15:08:06'),('0000-00-00 00:00:00','0000-00-00 00:00:00',NULL,1976,'0000-00-00 00:00:00'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2000,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2001,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2002,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2003,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00',NULL,2004,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','2018-05-18 15:08:06',2005,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','2018-05-18 15:08:06',2018,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','2018-05-18 15:08:06',2019,'2018-05-1 8 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','2018-05-18 15:08:06',2024,'2018-05-18 15:08:06'),('2018-05-18 17:08:06','0000-00-00 00:00:00','1999-12-31 23:00:00',2025,'2018-05-18 15:08:06'),('0000-00-00 00:00:00',NULL,'2018-05-18 15:08:06',2026,'2018-05-18 15:08:06'),('2018-05-18 17:08:07','0000-00-00 00:00:00','0000-00-00 00:00:00',2027,'0000-00-00 00:00:00'); + +--error ER_DUP_ENTRY +UPDATE `v1` t1, `t4` t2 +SET t1.`f2` = 6452736 WHERE t1.`f4` = 6272000; + +DROP VIEW v1; +DROP TABLE t3,t4; +SET @@sql_mode=@save_sql_mode; + +--echo # End of 10.2 tests diff --git a/sql/handler.cc b/sql/handler.cc index ae63640ae5c..d307433cf5d 100644 --- a/sql/handler.cc +++ b/sql/handler.cc @@ -2648,8 +2648,7 @@ int handler::ha_rnd_pos(uchar *buf, uchar *pos) DBUG_ENTER("handler::ha_rnd_pos"); DBUG_ASSERT(table_share->tmp_table != NO_TMP_TABLE || m_lock_type != F_UNLCK); - /* TODO: Find out how to solve ha_rnd_pos when finding duplicate update. */ - /* DBUG_ASSERT(inited == RND); */ + DBUG_ASSERT(inited == RND); TABLE_IO_WAIT(tracker, m_psi, PSI_TABLE_FETCH_ROW, MAX_KEY, 0, { result= rnd_pos(buf, pos); }) @@ -3307,6 +3306,10 @@ void handler::get_auto_increment(ulonglong offset, ulonglong increment, ulonglong nr; int error; MY_BITMAP *old_read_set; + bool rnd_inited= (inited == RND); + + if (rnd_inited && ha_rnd_end()) + return; old_read_set= table->prepare_for_keyread(table->s->next_number_index); @@ -3316,6 +3319,8 @@ void handler::get_auto_increment(ulonglong offset, ulonglong increment, DBUG_ASSERT(0); (void) extra(HA_EXTRA_NO_KEYREAD); *first_value= ULONGLONG_MAX; + if (rnd_inited) + ha_rnd_init(0); return; } @@ -3362,6 +3367,8 @@ void handler::get_auto_increment(ulonglong offset, ulonglong increment, ha_index_end(); table->restore_column_maps_after_keyread(old_read_set); *first_value= nr; + if (rnd_inited) + ha_rnd_init(0); return; } diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc index 8a9dd083911..cc1649b3c92 100644 --- a/sql/item_subselect.cc +++ b/sql/item_subselect.cc @@ -5855,12 +5855,17 @@ Ordered_key::cmp_keys_by_row_data_and_rownum(Ordered_key *key, } -void Ordered_key::sort_keys() +bool Ordered_key::sort_keys() { + /* Prepare table for random positioning (importent for innodb) */ + if (tbl->file->ha_rnd_init(0)) + return TRUE; my_qsort2(key_buff, (size_t) key_buff_elements, sizeof(rownum_t), (qsort2_cmp) &cmp_keys_by_row_data_and_rownum, (void*) this); /* Invalidate the current row position. */ cur_key_idx= HA_POS_ERROR; + tbl->file->ha_rnd_end(); + return FALSE; } @@ -6313,7 +6318,8 @@ subselect_rowid_merge_engine::init(MY_BITMAP *non_null_key_parts, /* Sort the keys in each of the indexes. */ for (uint i= 0; i < merge_keys_count; i++) - merge_keys[i]->sort_keys(); + if (merge_keys[i]->sort_keys()) + return TRUE; if (init_queue(&pq, merge_keys_count, 0, FALSE, subselect_rowid_merge_engine::cmp_keys_by_cur_rownum, NULL, diff --git a/sql/item_subselect.h b/sql/item_subselect.h index bd6a1bdc498..5366c759795 100644 --- a/sql/item_subselect.h +++ b/sql/item_subselect.h @@ -1287,7 +1287,7 @@ class Ordered_key : public Sql_alloc ++cur_key_idx; } - void sort_keys(); + bool sort_keys(); double null_selectivity(); /* diff --git a/sql/log_event.cc b/sql/log_event.cc index 8990e1953b6..c17c7ef6e06 100644 --- a/sql/log_event.cc +++ b/sql/log_event.cc @@ -12845,6 +12845,14 @@ Rows_log_event::write_row(rpl_group_info *rgi, if (table->file->ha_table_flags() & HA_DUPLICATE_POS) { DBUG_PRINT("info",("Locating offending record using rnd_pos()")); + error= table->file->ha_rnd_init(0); + if (error) + { + DBUG_PRINT("info",("rnd_init() returns error %d",error)); + table->file->print_error(error, MYF(0)); + DBUG_RETURN(error); + } + error= table->file->ha_rnd_pos(table->record[1], table->file->dup_ref); if (error) { @@ -12854,6 +12862,7 @@ Rows_log_event::write_row(rpl_group_info *rgi, table->file->print_error(error, MYF(0)); DBUG_RETURN(error); } + table->file->ha_rnd_end(); } else { diff --git a/sql/sql_insert.cc b/sql/sql_insert.cc index 307473cecbd..5593580dbca 100644 --- a/sql/sql_insert.cc +++ b/sql/sql_insert.cc @@ -881,7 +881,15 @@ bool mysql_insert(THD *thd,TABLE_LIST *table_list, #endif /* EMBEDDED_LIBRARY */ { if (duplic != DUP_ERROR || ignore) + { table->file->extra(HA_EXTRA_IGNORE_DUP_KEY); + if (table->file->ha_table_flags() & HA_DUPLICATE_POS && + table->file->ha_rnd_init(0)) + { + table->file->print_error(my_errno, MYF(0)); + goto abort; + } + } /** This is a simple check for the case when the table has a trigger that reads from it, or when the statement invokes a stored function @@ -942,7 +950,10 @@ bool mysql_insert(THD *thd,TABLE_LIST *table_list, { DBUG_PRINT("info", ("iteration %llu", iteration)); if (iteration && bulk_parameters_set(thd)) - goto abort; + { + error= 1; + goto values_loop_end; + } while ((values= its++)) { @@ -1094,7 +1105,11 @@ bool mysql_insert(THD *thd,TABLE_LIST *table_list, error=1; } if (duplic != DUP_ERROR || ignore) + { table->file->extra(HA_EXTRA_NO_IGNORE_DUP_KEY); + if (table->file->ha_table_flags() & HA_DUPLICATE_POS) + table->file->ha_rnd_end(); + } transactional_table= table->file->has_transactions(); @@ -1705,6 +1720,7 @@ int write_record(THD *thd, TABLE *table,COPY_INFO *info) goto err; if (table->file->ha_table_flags() & HA_DUPLICATE_POS) { + DBUG_ASSERT(table->file->inited == handler::RND); if (table->file->ha_rnd_pos(table->record[1],table->file->dup_ref)) goto err; } @@ -3177,6 +3193,10 @@ bool Delayed_insert::handle_inserts(void) max_rows= ULONG_MAX; // Do as much as possible } + /* Prepare table for random positioning (importent for innodb) */ + if (table->file->ha_rnd_init(0)) + goto err; + /* We can't use row caching when using the binary log because if we get a crash, then binary log will contain rows that are not yet @@ -3352,6 +3372,8 @@ bool Delayed_insert::handle_inserts(void) } } + table->file->ha_rnd_end(); + if (WSREP((&thd))) thd_proc_info(&thd, "insert done"); else @@ -3649,7 +3671,12 @@ select_insert::prepare(List<Item> &values, SELECT_LEX_UNIT *u) thd->cuted_fields=0; if (info.ignore || info.handle_duplicates != DUP_ERROR) + { table->file->extra(HA_EXTRA_IGNORE_DUP_KEY); + if (table->file->ha_table_flags() & HA_DUPLICATE_POS && + table->file->ha_rnd_init(0)) + DBUG_RETURN(1); + } if (info.handle_duplicates == DUP_REPLACE && (!table->triggers || !table->triggers->has_delete_triggers())) table->file->extra(HA_EXTRA_WRITE_CAN_REPLACE); @@ -3818,6 +3845,9 @@ bool select_insert::prepare_eof() if (!error && thd->is_error()) error= thd->get_stmt_da()->sql_errno(); + if (info.ignore || info.handle_duplicates != DUP_ERROR) + if (table->file->ha_table_flags() & HA_DUPLICATE_POS) + table->file->ha_rnd_end(); table->file->extra(HA_EXTRA_NO_IGNORE_DUP_KEY); table->file->extra(HA_EXTRA_WRITE_CANNOT_REPLACE); @@ -3929,6 +3959,11 @@ void select_insert::abort_result_set() { if (thd->locked_tables_mode <= LTM_LOCK_TABLES) table->file->ha_end_bulk_insert(); + if (table->file->inited) + table->file->ha_rnd_end(); + table->file->extra(HA_EXTRA_NO_IGNORE_DUP_KEY); + table->file->extra(HA_EXTRA_WRITE_CANNOT_REPLACE); + /* If at least one row has been inserted/modified and will stay in the table (the table doesn't have transactions) we must write to @@ -4341,7 +4376,12 @@ select_create::prepare(List<Item> &values, SELECT_LEX_UNIT *u) restore_record(table,s->default_values); // Get empty record thd->cuted_fields=0; if (info.ignore || info.handle_duplicates != DUP_ERROR) + { table->file->extra(HA_EXTRA_IGNORE_DUP_KEY); + if (table->file->ha_table_flags() & HA_DUPLICATE_POS && + table->file->ha_rnd_init(0)) + DBUG_RETURN(1); + } if (info.handle_duplicates == DUP_REPLACE && (!table->triggers || !table->triggers->has_delete_triggers())) table->file->extra(HA_EXTRA_WRITE_CAN_REPLACE); @@ -4524,9 +4564,6 @@ bool select_create::send_eof() */ exit_done= 1; // Avoid double calls - table->file->extra(HA_EXTRA_NO_IGNORE_DUP_KEY); - table->file->extra(HA_EXTRA_WRITE_CANNOT_REPLACE); - send_ok_packet(); if (m_plock) @@ -4602,13 +4639,6 @@ void select_create::abort_result_set() thd->locked_tables_list.unlock_locked_table(thd, create_info->mdl_ticket); } - if (m_plock) - { - mysql_unlock_tables(thd, *m_plock); - *m_plock= NULL; - m_plock= NULL; - } - if (table) { bool tmp_table= table->s->tmp_table; @@ -4619,9 +4649,21 @@ void select_create::abort_result_set() thd->restore_tmp_table_share(saved_tmp_table_share); } + if (table->file->inited && + (info.ignore || info.handle_duplicates != DUP_ERROR) && + (table->file->ha_table_flags() & HA_DUPLICATE_POS)) + table->file->ha_rnd_end(); table->file->extra(HA_EXTRA_NO_IGNORE_DUP_KEY); table->file->extra(HA_EXTRA_WRITE_CANNOT_REPLACE); table->auto_increment_field_not_null= FALSE; + + if (m_plock) + { + mysql_unlock_tables(thd, *m_plock); + *m_plock= NULL; + m_plock= NULL; + } + drop_open_table(thd, table, create_table->db, create_table->table_name); table=0; // Safety if (thd->log_current_statement && mysql_bin_log.is_open()) diff --git a/sql/sql_load.cc b/sql/sql_load.cc index 8c2f17dac3f..3283b962f65 100644 --- a/sql/sql_load.cc +++ b/sql/sql_load.cc @@ -638,6 +638,13 @@ int mysql_load(THD *thd,sql_exchange *ex,TABLE_LIST *table_list, thd->abort_on_warning= !ignore && thd->is_strict_mode(); + /* Prepare table for random positioning (importent for innodb) */ + if ((table_list->table->file->ha_table_flags() & HA_DUPLICATE_POS) && + table_list->table->file->ha_rnd_init(0)) + { + error= 1; + goto err; + } thd_progress_init(thd, 2); if (table_list->table->validate_default_values_of_unset_fields(thd)) { @@ -657,6 +664,9 @@ int mysql_load(THD *thd,sql_exchange *ex,TABLE_LIST *table_list, set_fields, set_values, read_info, *ex->enclosed, skip_lines, ignore); + if (table_list->table->file->ha_table_flags() & HA_DUPLICATE_POS) + table_list->table->file->ha_rnd_end(); + thd_proc_info(thd, "End bulk insert"); if (!error) thd_progress_next_stage(thd); diff --git a/sql/sql_select.cc b/sql/sql_select.cc index 91a6445c870..4c401ea9011 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -20317,6 +20317,12 @@ end_unique_update(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)), table->file->print_error(error,MYF(0)); /* purecov: inspected */ DBUG_RETURN(NESTED_LOOP_ERROR); /* purecov: inspected */ } + /* Prepare table for random positioning */ + bool rnd_inited= (table->file->inited == handler::RND); + if (!rnd_inited && + ((error= table->file->ha_index_end()) || + (error= table->file->ha_rnd_init(0)))) + DBUG_RETURN(NESTED_LOOP_ERROR); if (table->file->ha_rnd_pos(table->record[1],table->file->dup_ref)) { table->file->print_error(error,MYF(0)); /* purecov: inspected */ @@ -20330,6 +20336,10 @@ end_unique_update(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)), table->file->print_error(error,MYF(0)); /* purecov: inspected */ DBUG_RETURN(NESTED_LOOP_ERROR); /* purecov: inspected */ } + if (!rnd_inited && + ((error= table->file->ha_rnd_end()) || + (error= table->file->ha_index_init(0, 0)))) + DBUG_RETURN(NESTED_LOOP_ERROR); } if (join->thd->check_killed()) { diff --git a/sql/sql_update.cc b/sql/sql_update.cc index 11ffa684216..6d4c11d494a 100644 --- a/sql/sql_update.cc +++ b/sql/sql_update.cc @@ -211,6 +211,10 @@ static void prepare_record_for_error_message(int error, TABLE *table) bitmap_union(table->read_set, &unique_map); /* Tell the engine about the new set. */ table->file->column_bitmaps_signal(); + /* Prepare table for random positioning (importent for innodb) */ + if (table->file->ha_index_or_rnd_end() || + table->file->ha_rnd_init(0)) + DBUG_VOID_RETURN; /* Read record that is identified by table->file->ref. */ (void) table->file->ha_rnd_pos(table->record[1], table->file->ref); /* Copy the newly read columns into the new record. */
participants (1)
-
Oleksandr Byelkin