The max and min search length for the MySQL database vary based on the
engine for the underlying table. For MyISAM tables, the variables are
ft_max_word_len and ft_min_word_len, but for InnoDB tables the
variables are innodb_ft_max_token_size and innodb_ft_min_token_size.
Take the posts table type into account when setting the max and min
search length.
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