FTS Flatcurve
Search K

Appearance

Configuration ​

See Dovecot FTS Configuration for configuration information regarding general FTS plugin options.

NOTE

Flatcurve REQUIRES the core Dovecot FTS stemming feature.

Required Configuration ​

The following is required to enable FTS Flatcurve in Dovecot configuration:

# Enable both "fts" and "fts_flatcurve" plugins
mail_plugins = $mail_plugins fts fts_flatcurve

plugin {
  # Define "flatcurve" as the FTS driver.
  fts = flatcurve

  # These are not flatcurve settings, but required for Dovecot FTS. See
  # Dovecot FTS Configuration link above for further information.
  fts_languages = en es de
  fts_tokenizers = generic email-address

  # Maximum term length can be set via the 'maxlen' argument (maxlen is
  # specified in bytes, not number of UTF-8 characters)
  fts_tokenizer_email_address = maxlen=100
  fts_tokenizer_generic = algorithm=simple maxlen=30

  # OPTIONAL: Recommended default FTS core configuration
  fts_filters = normalizer-icu snowball stopwords
  fts_filters_en = lowercase snowball english-possessive stopwords
}

NFS Recommendation ​

To prevent concurrent writes to the Xapian database files, Dovecot relies on file locking.

If using NFS, the VOLATILEDIR parameter for the mail_location configuration option should be used to perform this locking locally as opposed to on the remote server.

Plugin Settings ​

The default parameters should be fine for most people.

These settings must go in a plugin {} block. Example:

plugin {
  fts_flatcurve_<setting> = <setting_value>
}

fts_flatcurve_commit_limit

  • Default: 500
  • Value: integer, set to 0 to use the Xapian default

Commit database changes after this many documents are updated. Higher commit limits will result in faster indexing for large transactions (i.e. indexing a large mailbox) at the expense of high memory usage. The default value should be sufficient to allow indexing in a 256 MB maximum size process.

fts_flatcurve_min_term_size

  • Default: 2
  • Value: integer

The minimum number of characters in a term to index.

fts_flatcurve_optimize_limit

  • Default: 10
  • Value: integer, set to 0 to disable

Once the database reaches this number of shards, automatically optimize the DB at shutdown.

fts_flatcurve_rotate_size

  • Default: 5000
  • Value: integer, set to 0 to disable rotation

When the "current" fts database reaches this number of messages, it is rotated to a read-only database and replaced by a new write DB. Most people should not change this setting.

fts_flatcurve_rotate_time

  • Default: 5000
  • Value: integer, set to 0 to disable rotation

When the "current" fts database exceeds this length of time (in msecs) to commit changes, it is rotated to a read-only database and replaced by a new write DB. Most people should not change this setting.

  • Default: no
  • Value: boolean (yes or no)

If enabled, allows substring searches (RFC 3501 compliant). However, this requires significant additional storage space. Most users today expect "Google-like" behavior, which is prefix searching, so substring searching is arguably not the "modern, expected" behavior. Therefore, even though it is not strictly RFC compliant, prefix (non-substring) searching is enabled by default.