Hi, Sachin!
On Mar 12, Sachin Setiya wrote:
> revision-id: 1aa6d5bdbec (mariadb-10.4.3-63-g1aa6d5bdbec)
> parent(s): b5d2e8577ef
> author: Sachin Setiya <[email protected]>
> committer: sachin <[email protected]>
> timestamp: 2019-03-12 19:29:58 +0530
> message:
>
> MDEV-18888 Server crashes in Item_field::register_field_in_read_map upon...
> MODIFY COLUMN
>
> Do Not create prefix field for long unique key
>
> diff --git a/sql/table.cc b/sql/table.cc
> index 4da873b2e8f..5ca284fd8dd 100644
> --- a/sql/table.cc
> +++ b/sql/table.cc
> @@ -3709,7 +3709,33 @@ enum open_frm_error open_table_from_share(THD *thd,
> TABLE_SHARE *share,
> Field *field= key_part->field= outparam->field[key_part->fieldnr -
> 1];
>
> if (field->key_length() != key_part->length &&
> - !(field->flags & BLOB_FLAG))
> + !(field->flags & BLOB_FLAG) &&
> + /*
> + MDEV-18888
> + We will not make copy of the field because if we do this this
> this will
> + make this test case to fail
> + CREATE TABLE t1 (
> + a CHAR(128),
> + b CHAR(128) AS (a),
> + c varchar(5000),
> + UNIQUE(c,b(64))
> + ) ENGINE=InnoDB;
> + And the reason for this is because Item_func_hash will
> Item_field based on
> + this new field. But if this field is virtual field then since
> it is created
> + before calling parse_vcol_defs so it does not have
> field->vcol_info->expr item
> + initiated. And this will make segfault when
> field->vcol_info->expr is accessed.
> + So the question may be why similar unique with just virtual
> column is not crashing ?
> + CREATE TABLE t2 (
> + a CHAR(128),
> + b CHAR(128) AS (a),
> + c char(128) as (a+b),
> + UNIQUE(a, c(64))
> + ) ENGINE=InnoDB;
> + In this case also new prefix field will be created whose
> vcol_info->expr will be NULL.
> + But Since this key is not a long unique in
> innodb_base_col_setup field will be
> + table->field[i] which will have not null vcol_info->expr
> + */
> + key_info->algorithm != HA_KEY_ALG_LONG_HASH)
don't put a comment (particularly a long one) inside the if(), move it
to be before the if(), please.
and I'd used a simpler comment, like "there's no need to create a prefix
Field for HA_KEY_ALG_LONG_HASH indexes, as they implement prefixing via
Iten_func_left anyway (see parse_vcol_defs()"
> {
> /*
> We are using only a prefix of the column as a key:
Regards,
Sergei
Chief Architect MariaDB
and [email protected]
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