Full text search

By default, when your IMAP client searches for an email containing some text in its body, dovecot will read all your email sequentially. This is very slow and IO intensive. To speed body searches up, it is possible to index emails with the fts_flatcurve dovecot plugin.

Enabling full text search

To enable indexing for full text search here is an example configuration.

{
  mailserver = {
    # ...
    fullTextSearch = {
      enable = true;
      # index new email as they arrive
      autoIndex = true;
      # only query index
      fallback = false;
    };
  };
}

Disabling the mailserver.fullTextSearch.fallback option tells dovecot to fail any body search query that cannot use an index. This prevents Dovecot to fall back to the IO-intensive brute force search.

If you set mailserver.fullTextSearch.autoIndex to false, indices will be created when the IMAP client issues a search query, so latency will be high.

Resource requirements

Indices created by the full text search feature can take more disk space than the emails themselves. By default, they are kept within the maildir. When enabling the full text search feature, it is recommended to move indices in a different location, such as (/var/lib/dovecot/indices) by configuring mailserver.indexDir.

Warning

When the value of the mailserver.indexDir option is changed, all dovecot indices needs to be recreated: clients would need to resynchronize.

Indexation itself is rather resource intensive, in CPU, and for emails with large headers, in memory as well. Initial indexation of existing emails can take hours. If the indexer worker is killed or segfaults during indexation, it can be that it tried to allocate more memory than allowed. You can increase the default memory limit through mailserver.fullTextSearch.memoryLimit.

Mitigating resources requirements

You can: