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MDEV-25803 Inplace ALTER breaks MyISAM/Aria table when order of keys is changed

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mysql_prepare_create_table() does my_qsort(sort_keys) on key
info. This sorting is indeterministic: a table is created with one
order and inplace alter may overwrite frm with another order. Since
inplace alter does nothing about key info for MyISAM/Aria storage
engines this results in discrepancy between frm and storage engine key
definitions.

The fix avoids the sorting of keys when no new keys added by ALTER
(and this is ok for MyISAM/Aria since it cannot add new keys inplace).

There is a case when implicit primary key may be changed when removing
NOT NULL from the part of unique key. In that case we update
modified_primary_key which is then used to not skip key sorting.

According to is_candidate_key() there is no other cases when primary
key may be changed implicitly.

Notes:

mi_keydef_write()/mi_keyseg_write() are used only in mi_create(). They
should be used in ha_inplace_alter_table() as well.

Aria corruption detection is unimplemented: maria_check_definition()
is never used!

MySQL 8.0 has this bug as well as of 8.0.26.
This commit is contained in:
Aleksey Midenkov
2021-11-03 12:31:47 +03:00
parent a8ded39557
commit b3bdc1c142
8 changed files with 114 additions and 12 deletions
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52
sql/sql_table.cc
View File

@ -4435,9 +4435,30 @@ without_overlaps_err:
my_message(ER_WRONG_AUTO_KEY, ER_THD(thd, ER_WRONG_AUTO_KEY), MYF(0));
DBUG_RETURN(TRUE);
}
/* Sort keys in optimized order */
my_qsort((uchar*) *key_info_buffer, *key_count, sizeof(KEY),
(qsort_cmp) sort_keys);
/*
We cannot do qsort of key info if MyISAM/Aria does inplace. These engines
do not synchronise key info on inplace alter and that qsort is
indeterministic (MDEV-25803).
Yet we do not know whether we do inplace or not. That detection is done
after this create_table_impl() and that cannot be changed because of chicken
and egg problem (inplace processing requires key info made by
create_table_impl()).
MyISAM/Aria cannot add index inplace so we are safe to qsort key info in
that case. And if we don't add index then we do not need qsort at all.
*/
if (!(create_info->options & HA_SKIP_KEY_SORT))
{
/*
Sort keys in optimized order.
Note: PK must be always first key, otherwise init_from_binary_frm_image()
can not understand it.
*/
my_qsort((uchar*) *key_info_buffer, *key_count, sizeof(KEY),
(qsort_cmp) sort_keys);
}
create_info->null_bits= null_fields;
/* Check fields. */
@ -8380,7 +8401,6 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
uint used_fields, dropped_sys_vers_fields= 0;
KEY *key_info=table->key_info;
bool rc= TRUE;
bool modified_primary_key= FALSE;
bool vers_system_invisible= false;
Create_field *def;
Field **f_ptr,*field;
@ -8804,6 +8824,12 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
if (key_info->flags & HA_INVISIBLE_KEY)
continue;
const char *key_name= key_info->name.str;
const bool primary_key= table->s->primary_key == i;
const bool explicit_pk= primary_key &&
!my_strcasecmp(system_charset_info, key_name,
primary_key_name);
const bool implicit_pk= primary_key && !explicit_pk;
Alter_drop *drop;
drop_it.rewind();
while ((drop=drop_it++))
@ -8817,7 +8843,7 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
if (table->s->tmp_table == NO_TMP_TABLE)
{
(void) delete_statistics_for_index(thd, table, key_info, FALSE);
if (i == table->s->primary_key)
if (primary_key)
{
KEY *tab_key_info= table->key_info;
for (uint j=0; j < table->s->keys; j++, tab_key_info++)
@ -8904,13 +8930,19 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
}
if (!cfield)
{
if (table->s->primary_key == i)
modified_primary_key= TRUE;
if (primary_key)
alter_ctx->modified_primary_key= true;
delete_index_stat= TRUE;
if (!(kfield->flags & VERS_SYSTEM_FIELD))
dropped_key_part= key_part_name;
continue; // Field is removed
}
DBUG_ASSERT(!primary_key || kfield->flags & NOT_NULL_FLAG);
if (implicit_pk && !alter_ctx->modified_primary_key &&
!(cfield->flags & NOT_NULL_FLAG))
alter_ctx->modified_primary_key= true;
key_part_length= key_part->length;
if (cfield->field) // Not new field
{
@ -8959,7 +8991,7 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
{
if (delete_index_stat)
(void) delete_statistics_for_index(thd, table, key_info, FALSE);
else if (modified_primary_key &&
else if (alter_ctx->modified_primary_key &&
key_info->user_defined_key_parts != key_info->ext_key_parts)
(void) delete_statistics_for_index(thd, table, key_info, TRUE);
}
@ -9003,7 +9035,7 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
key_type= Key::SPATIAL;
else if (key_info->flags & HA_NOSAME)
{
if (! my_strcasecmp(system_charset_info, key_name, primary_key_name))
if (explicit_pk)
key_type= Key::PRIMARY;
else
key_type= Key::UNIQUE;
@ -10589,6 +10621,8 @@ do_continue:;
tmp_disable_binlog(thd);
create_info->options|=HA_CREATE_TMP_ALTER;
if (!(alter_info->flags & ALTER_ADD_INDEX) && !alter_ctx.modified_primary_key)
create_info->options|= HA_SKIP_KEY_SORT;
create_info->alias= alter_ctx.table_name;
error= create_table_impl(thd, alter_ctx.db, alter_ctx.table_name,
alter_ctx.new_db, alter_ctx.tmp_name,