# InnoDB full-text search improvements

# Ignoring stopword list

By default, all Full-Text Search indexes check the [stopwords list](https://dev.mysql.com/doc/refman/8.0/en/fulltext-stopwords.html), to see if any indexed elements contain words on that list.

Using this list for n-gram indexes isn’t always suitable, for example, any
item that contains `a` or `i` will be ignored. Another word that can’t be
searched is `east`, this one will find no matches because `a` is on the
FTS stopword list.

To resolve this issue, *Percona Server for MySQL* has the
`innodb_ft_ignore_stopwords` variable to control whether
*InnoDB* Full-Text Search should ignore the stopword list.

Although this variable is introduced to resolve n-gram issues, it affects all Full-Text Search indexes as well.

Being a stopword doesn’t just mean being one of the predefined
words from the list. Tokens shorter than [innodb_ft_min_token_size](https://dev.mysql.com/doc/refman/8.0/en/innodb-parameters.html#sysvar_innodb_ft_min_token_size)
or longer than [innodb_ft_max_token_size](https://dev.mysql.com/doc/refman/8.0/en/innodb-parameters.html#sysvar_innodb_ft_max_token_size)
are also considered stopwords. Therefore, when
innodb_ft_ignore_stopwords is set to `ON` even for non-ngram
FTS, `innodb_ft_min_token_size` / `innodb_ft_max_token_size` will be
ignored meaning that in this case very short and very long words will
also be indexed.

## System variables

### `innodb_ft_ignore_stopwords`

| Option       | Description     |
|--------------|-----------------|
| Command-line | Yes             |
| Config file  | Yes             |
| Scope        | Session, Global |
| Dynamic      | Yes             |
| Data type    | Boolean         |
| Default      | OFF             |

When enabled, this variable will instruct *InnoDB* Full Text Search
parser to ignore the stopword list when building/updating an FTS index.