Dovecot Dictionaries¶

Dovecot’s lib-dict can be used to access simple key-value databases. This is used by, for example, Quota Backend: dict, Key-value authentication (dict) database, Last Login Plugin, and IMAP METADATA. The dictionaries can be accessed either directly by the mail processes or they can be accessed via Dictionary Proxy Process processes.

Currently supported dict backends are:

Name	Description
file	Flat Files
fs	FS (lib-fs wrapper)
ldap	LDAP (read only)
memcached-ascii	Memcached (ASCII protocol)
memcached-binary	Memcached (Binary protocol)
proxy	Proxy
redis	Redis
sql	SQL

Connection Pooling¶

The SQL driver keeps a maximum of 10 unused SQL connections open (infinitely) and reuses them for SQL dict lookup requests.

New in version v2.3.17.

Starting version 2.3.17, the dict server process keeps the last 10 idle dict backends cached for maximum of 30 seconds. Practically this acts as a connection pool for Redis, Memcached (ASCII Protocol) and LDAP. Note that this doesn’t affect dict-sql, because it already had its own internal cache.

Flat Files¶

file:<path>

The file will simply contain all the keys that are used. Not very efficient for large databases, but good for small ones such as a single user’s quota.

Filesystem (lib-fs wrapper)¶

New in version v2.2.11.

fs:<driver>:<driver args>

This is a wrapper for lib-fs, which most importantly has the posix backend. So using:

fs:posix:prefix=/var/lib/dovecot/dict/

Would create a separate file under /var/lib/dovecot/dict for each key.

LDAP¶

New in version v2.2.24.

LDAP support is very similar to SQL support, but there is no write support.

Note that the LDAP backend must be used via Proxy.

See LDAP.

Configuration¶

dict {
  somedict = ldap:/path/to/dovecot-ldap-dict.conf.ext
}

Parameters in .ext file:

Parameter	Required	Description
`uri`	YES	LDAP connection URI as expected by OpenLDAP.
`bind_dn`	NO	DN or upn to use for binding. (default: none)
`debug`	NO	Enable debug. `0` = off (default), `1` = on.
`password`	NO	Password to use, only SIMPLE auth is supported at the moment. (default: none)
`timeout`	NO	How long to wait for reply, in seconds. (default: 30 seconds)
`tls`	NO	Use TLS? `yes`: Require either ldaps or successful start TLS `try`: Send start TLS if necessary (default) `no`: Do not send start TLS.

Configuration Examples¶

To map a key to a search:

map {
  pattern = priv/test/mail
  filter = (mail=*)  # the () is required
  base_dn = ou=container,dc=domain
  username_attribute = uid # default is cn
  value_attribute = mail
}

To do a more complex search:

map {
  pattern = priv/test/mail/$location
  filter = (&(mail=*)(location=%{location}) # the () is required
  base_dn = ou=container,dc=domain
  username_attribute = uid # default is cn
  value_attribute = mail

  fields {
    location=$location
  }
}

Memcached (ASCII Protocol)¶

Note

Memcached dict support is considered deprecated and will be removed in the future. Users are advised to upgrade to Redis.

New in version v2.2.9.

This driver uses the “legacy” Memcache ASCII protocol.

https://github.com/memcached/memcached/blob/master/doc/protocol.txt

memcached_ascii:param=value:param2=value2:...

Supported parameters are:

Parameter	Required	Description
`host`	NO	Memcached server host (default: `127.0.0.1`)
`port`	NO	Memcached server port (default: `11211`)
`prefix`	NO	Prefix to add to all keys (default: none)
`timeout_msecs`	NO	Abort lookups after specified number of milliseconds (default: `30000`)

Memcached (Binary Protocol)¶

Note

Memcached dict support is considered deprecated and will be removed in the future. Users are advised to upgrade to Redis.

New in version v2.2.9.

This driver uses the “new” Memcache binary protocol.

See: https://code.google.com/p/memcached/wiki/MemcacheBinaryProtocol

memcached:param=value:param2=value2:...

Supported parameters are:

Parameter	Required	Description
`host`	NO	Memcached server host (default: `127.0.0.1`)
`port`	NO	Memcached server port (default: `11211`)
`prefix`	NO	Prefix to add to all keys (default: none)
`timeout_msecs`	NO	Abort lookups after specified number of milliseconds (default: `30000`)

Proxy¶

proxy:[<dict path>]:<destination dict>

Proxying is used to perform all dictionary accessing via the dict processes. (The dict processes exist only if dict proxying is used.) This is especially useful with backends where their initialization is relatively expensive, such as SQL. The dict processes will perform connection pooling.

If <dict path> is specified, it points to the socket where the dict server is answering. The default is to use $base_dir/dict. Usually this is changed to dict-async if the dict backend support asynchronous lookups (e.g. ldap, pgsql, cassandra). The dict-async service allows more than one client, so this configuration prevents creating unnecessarily many dict processes.

The <destination dict> contains the dict name in the dict { .. } settings. For example: proxy:dict-async:quota.

See Dictionary Proxy Process for more information about the dict server.

Redis¶

New in version v2.2.9.

Note that Redis backend is recommended to be used via Proxy to support connection pooling. Also, currently using Redis without proxying may cause crashes.

redis:param=value:param2=value2:...

Supported parameters are:

Parameter	Required	Description
`db`	NO	Database number (default: `0`)
`expire_secs`	NO	Expiration value for all keys (in seconds) (default: no expiration)
`host`	NO	Redis server host (default: `127.0.0.1`)
`port`	NO	Redis server port (default: `11211`)
`prefix`	NO	Prefix to add to all keys (default: none)
`timeout_msecs`	NO	Abort lookups after specified number of milliseconds (default: `30000`)

SQL¶

Note that the SQL backend must be used via Proxy.

<sql driver>:<path to dict-sql config>

The <sql driver> component contains the SQL driver name, such as mysql, pgsql, sqlite, or cassandra.

The dict-sql config file consists of SQL server configuration and mapping of keys to SQL tables/fields.

See SQL.

SQL Connect String¶

connect = host=localhost dbname=mails user=sqluser password=sqlpass

The connect setting is exactly the same as used for SQL Authentication.

SQL Mapping¶

SQL mapping is done with a dict key pattern and fields. When a dict lookup or update is done, Dovecot goes through all the maps and uses the first one whose pattern matches the dict key.

For example when using dict for a per-user quota value the map looks like:

map {
  pattern = priv/quota/storage
  table = quota
  username_field = username
  value_field = quota_bytes
}

The dict key must match exactly priv/quota/storage. The dict keys are hardcoded in the Dovecot code, so depending on what functionality you’re configuring you need to know the available dict keys used it.
This is a private dict key (priv/ prefix), which means that there must be a username_field. The username_field is assumed to be (at least part of) the primary key. In this example we don’t have any other primary keys.
With MySQL the above map translates to SQL queries:
- SELECT quota_bytes FROM quota WHERE username = '$username_field'
- INSERT INTO quota (username, quota_bytes) VALUES ('$username_field', '$value') ON DUPLICATE KEY UPDATE quota_bytes='$value'

You can also access multiple SQL fields. For example acl_shared_dict can contain:

map {
  pattern = shared/shared-boxes/user/$to/$from
  table = user_shares
  value_field = dummy

  fields {
    from_user = $from
    to_user = $to
  }
}

The acl_shared_dict always uses 1 as the value, so here the value_field is called dummy.
The SQL from_user and to_user fields are the interesting ones. Typically the extra fields would be part of the primary key.
With MySQL the above map translates to SQL queries:
- SELECT dummy FROM user_shares WHERE from_user = '$from' AND to_user = '$to'
- INSERT INTO user_shares (from_user, to_user, dummy) VALUES ('$from', '$to', '$value') ON DUPLICATE KEY UPDATE dummy='$value'

SQL dict with mail_attribute_dict¶

It’s possible to implement mail_attribute_dict also with SQL dict.

Warning

Using shared attributes in mail_attribute_dict requires the mailbox GUID to be unique between users. This is not the case when mails were migrated via imapc, because it uses a hash of the mailbox name as the GUID. So every migrated user would have exactly the same INBOX GUID, preventing the use of dict-sql. It is currently not possible to add a username as an additional unique identifier.

# CREATE TABLE mailbox_private_attributes (
#   username VARCHAR(255),
#   mailbox_guid VARCHAR(32),
#   attr_key VARCHAR(255),
#   value TEXT,
#   PRIMARY KEY (username, mailbox_guid, attr_key)
# )
map {
  pattern = priv/$mailbox_guid/$key
  table = mailbox_private_attributes
  username_field = user
  value_field = value

  fields {
    attr_key = $key
    mailbox_guid = $mailbox_guid
  }
}

# CREATE TABLE mailbox_shared_attributes (
#   mailbox_guid VARCHAR(32),
#   attr_key VARCHAR(255),
#   value TEXT,
#   PRIMARY KEY (mailbox_guid, attr_key)
# );
map {
  pattern = shared/$mailbox_guid/$key
  table = mailbox_shared_attributes
  value_field = value

  fields {
    attr_key = $key
    mailbox_guid = $mailbox_guid
  }
}

# Due to a bug, it's also necessary for now to use the following table
# to catch accesses to /private and /shared root key lookups.
# This is unnecessary in v2.3.20 and later:
#
# CREATE TABLE mailbox_private_none (
#   username VARCHAR(255) DEFAULT "",
#   value TEXT,
#   PRIMARY KEY (username)
# ) ROW_FORMAT=DYNAMIC;
map {
  pattern = priv/
  table = mailbox_attributes_none
  username_field = username
  value_field = value
}
map {
  pattern = shared/
  table = mailbox_attributes_none
  value_field = value
}

Dovecot Dictionaries¶

Connection Pooling¶

Flat Files¶

Filesystem (lib-fs wrapper)¶

LDAP¶

Configuration¶

Configuration Examples¶

Memcached (ASCII Protocol)¶

Memcached (Binary Protocol)¶

Proxy¶

Redis¶

SQL¶

SQL Connect String¶

SQL Mapping¶

SQL dict with mail_attribute_dict¶

See Also¶

Navigation

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