Martin Weinelt
70 lines
2.5 KiB
ReStructuredText
70 lines
2.5 KiB
ReStructuredText
Full text search
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==========================
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By default, when your IMAP client searches for an email containing some
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text in its *body*, dovecot will read all your email sequentially. This
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is very slow and IO intensive. To speed body searches up, it is possible to
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*index* emails with the ``fts_flatcurve`` dovecot plugin.
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Enabling full text search
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To enable indexing for full text search here is an example configuration.
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.. code:: nix
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{
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mailserver = {
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# ...
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fullTextSearch = {
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enable = true;
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# index new email as they arrive
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autoIndex = true;
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# only query index
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fallback = false;
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};
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};
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}
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Disabling the :option:`mailserver.fullTextSearch.fallback` option tells dovecot
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to fail any body search query that cannot use an index. This prevents Dovecot to
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fall back to the IO-intensive brute force search.
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If you set :option:`mailserver.fullTextSearch.autoIndex` to ``false``, indices
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will be created when the IMAP client issues a search query, so latency will
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be high.
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Resource requirements
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~~~~~~~~~~~~~~~~~~~~~~~~
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Indices created by the full text search feature can take more disk space than
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the emails themselves. By default, they are kept within the maildir. When
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enabling the full text search feature, it is recommended to move indices in a
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different location, such as (``/var/lib/dovecot/indices``) by configuring
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:option:`mailserver.indexDir`.
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.. warning::
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When the value of the :option:`mailserver.indexDir` option is changed, all
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dovecot indices needs to be recreated: clients would need to resynchronize.
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Indexation itself is rather resource intensive, in CPU, and for emails with
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large headers, in memory as well. Initial indexation of existing emails can take
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hours. If the indexer worker is killed or segfaults during indexation, it can be
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that it tried to allocate more memory than allowed. You can increase the default
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memory limit through :option:`mailserver.fullTextSearch.memoryLimit`.
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Mitigating resources requirements
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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You can:
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* exclude some headers from indexation with :option:`mailserver.fullTextSearch.headerExcludes`
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* disable expensive token normalisation in :option:`mailserver.fullTextSearch.filters`
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* disable automatic indexation for individual mailboxes by overriding
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`fts_autoindex`_ on the mailbox level. This is exposed via
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:option:`mailserver.mailboxes`, where all default mailboxes are defined.
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.. _fts_autoindex: https://doc.dovecot.org/main/core/plugins/fts.html#fts_autoindex
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