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MDEV-16465 Invalid (old?) table or database name or hang in ha_innobase::delete_table and log semaphore wait upon concurrent DDL with foreign keys

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ALTER TABLE locks the table with TL_READ_NO_INSERT, to prevent the
source table modifications while it's being copied. But there's an
indirect way of modifying a table, via cascade FK actions.

After previous commits, an attempt to modify an FK parent table
will cause FK children to be prelocked, so the table-being-altered
cannot be modified by a cascade FK action, because ALTER holds a
lock and prelocking will wait.

But if a new FK is being added by this very ALTER, then the target
table is not locked yet (it's a temporary table). So, we have to
lock FK parents explicitly.
This commit is contained in:
Sergei Golubchik
2018-07-19 01:03:14 +02:00
parent e81f101dac
commit 9180e8666b
6 changed files with 132 additions and 9 deletions
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47
sql/sql_table.cc
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@ -9057,8 +9057,10 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
alter_ctx.tmp_name, strlen(alter_ctx.tmp_name),
alter_ctx.tmp_name, TL_READ_NO_INSERT);
/* Table is in thd->temporary_tables */
(void) open_temporary_table(thd, &tbl);
if (open_temporary_table(thd, &tbl))
goto err_new_table_cleanup;
new_table= tbl.table;
DBUG_ASSERT(new_table);
}
else
{
@ -9067,9 +9069,48 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
new_table= open_table_uncached(thd, new_db_type, alter_ctx.get_tmp_path(),
alter_ctx.new_db, alter_ctx.tmp_name,
true, true);
if (!new_table)
goto err_new_table_cleanup;
/*
Normally, an attempt to modify an FK parent table will cause
FK children to be prelocked, so the table-being-altered cannot
be modified by a cascade FK action, because ALTER holds a lock
and prelocking will wait.
But if a new FK is being added by this very ALTER, then the target
table is not locked yet (it's a temporary table). So, we have to
lock FK parents explicitly.
*/
if (alter_info->flags & Alter_info::ADD_FOREIGN_KEY)
{
List <FOREIGN_KEY_INFO> fk_list;
List_iterator<FOREIGN_KEY_INFO> fk_list_it(fk_list);
FOREIGN_KEY_INFO *fk;
/* tables_opened can be > 1 only for MERGE tables */
DBUG_ASSERT(tables_opened == 1);
DBUG_ASSERT(&table_list->next_global == thd->lex->query_tables_last);
new_table->file->get_foreign_key_list(thd, &fk_list);
while ((fk= fk_list_it++))
{
if (table_already_fk_prelocked(table_list, fk->referenced_db,
fk->referenced_table, TL_READ_NO_INSERT))
continue;
TABLE_LIST *tl= (TABLE_LIST *) thd->alloc(sizeof(TABLE_LIST));
tl->init_one_table_for_prelocking(fk->referenced_db->str, fk->referenced_db->length,
fk->referenced_table->str, fk->referenced_table->length,
NULL, TL_READ_NO_INSERT, false, NULL, 0,
&thd->lex->query_tables_last);
}
if (open_tables(thd, &table_list->next_global, &tables_opened, 0,
&alter_prelocking_strategy))
goto err_new_table_cleanup;
}
}
if (!new_table)
goto err_new_table_cleanup;
/*
Note: In case of MERGE table, we do not attach children. We do not
copy data for MERGE tables. Only the children have data.