Core schema changes to accommodate utf8mb4 index length limits

[drbyte]

Note: the cases where the field length was changed instead of the index are either primary keys or fields whose length can afford to be shorter.

• field lengths where shorter will suffice
• lengths on hybrid indexes
• Session Length: PHP allows for 256

Supporting 256 chars in db requires MySQL 5.0.3 or newer.

[torvista]

In phpmyadmin, on the sessions table it will not allow varchar(256) with InnoDB, even with utf8_general_ci (10.1.29-MariaDB).

[drbyte]

Some reading I've done further suggests it may require MySQL higher than 5.7.7 or MariaDB higher than 10.2.2

What error message/s do you get?

[torvista]

10.1.29-MariaDB is the latest currently offered by Xampp for php 7.2.
Maybe utf8mb4 is not ready for primetime yet...

[torvista]

I note the ZC156 installer appears to complete successfully despite having failed to create this table: no error flagged (subsequently the admin login fails with a debug).

[drbyte]

Did whos_online throw any errors?
From my reading I understand that unique keys need to also support the full length * 4, so would expect the same error to occur when creating the session_id unique index on the whos_online table, too.

I "get" that the sessions table is doing this, because the primary key is an index, actually a unique-index.

It's frustrating that zc_install doesn't seem to be getting flagged about the error. Grrr.

[torvista]

whos_oline is created ok: has varchar(256) and is still MyISAM.

[drbyte]

Puzzling

I have mariadb 10.2.12 installed, so my testing results are a bit different.

[torvista]

I've installed ZC158 many times on Xampp having created the DB with
CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_520_ci;
with no problem.
But I've just started to tryout Laragon and the install did not create table products.description: needing both varchars at 250 to create the table (they are set differently at 254/255).
Subsequently when playing with this value in the database admin tool Heidi, it won't accept more than 250. The error is the same as that created in the installer debug.

This is php 7.4.16, mysql 5.7.24.

[drbyte]

MySQL has significantly tinier capacity (1000) than MariaDB does (over 3000) on index lengths.

The issue is that if you want to support mb4 on MySQL then you can NEVER have columns longer than 250 characters, because each character requires 4 bytes. 250 * 4 = 1000 which is MySQL's maximum index size.

The problem is compounded many times over when indexing multiple columns.
And even worse when storeowners want to stuff even longer values in those columns.

There are some options:

• don't use MySQL (use MariaDB instead)
• use shorter index lengths (see below) on those fields
• drop (or skip creating) indexes on those longer fields (you'll have to edit the .SQL file before installing)
• use shorter column lengths (you'll have to edit the .SQL file before installing)

For v158 I've reverted the default install to use a shorter length.