Description:
The document at https://dev.mysql.com/doc/refman/8.0/en/innodb-undo-tablespaces.html says:
"The initial size may differ when a new undo tablespace is created by a truncate operation. In this case, if the file extension size is larger than 16MB, and the previous file extension occurred within the last second, the new undo tablespace is created at a quarter of the size defined by the innodb_max_undo_log_size variable."
In the above document, "the size defined by the innodb_max_undo_log_size variable" should be replaced by "the old undo tablespace's size";
Refer to the following code in function trx_undo_truncate_tablespace:
```
if (space != nullptr && space->m_undo_extend > UNDO_INITIAL_SIZE_IN_PAGES &&
space->m_last_extended.elapsed() < 1000) {
/* UNDO is being extended aggressively, don't reduce size to default. */
n_pages = fil_space_get_size(old_space_id) / 4;
}
``
How to repeat:
This is a documentation issue.
Suggested fix:
I think the following description is more reasonable:
"The initial size may differ when a new undo tablespace is created by a truncate operation. In this case, if the file extension size is larger than 16MB, and the previous file extension occurred within the last second, the new undo tablespace is created at a quarter of the old undo tablespace's size."
