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# Search Tiers

The Xapian search engine supports searching from multiple databases at once, creating a tiered database structure. To use Xapian, these tiers must be defined in imapd.conf(5) with the defaultsearchtier and searchpartition-name settings.

## Default Search Tier name

Specify the name of the default search tier using the defaultsearchtier setting:

> `defaultsearchtier:` <empty string>

> > Name of the default tier that messages will be indexed to. Search indexes can be organized in tiers to allow index storage in different directories and physical media. See the man page of squatter for details. The default search tier also requires the definition of an according searchtierpartition-name entry.

> > This option MUST be specified for xapian search.

## Search Tier Partition location

Each search tier to be used requires a partition location be specified via a searchpartition-name setting, wherein “name” is replaced with the name of the mail spool for which this search partition is to be used, and prepended by the name of the tier with which it is associated:

    {tier}searchpartition-{spool}

Again, building on our examples from Spool Directories, here we have three spool partitions defined, so we need three search partitions for each tier. In this example, with just a single tier, we will be adding three search partitions.

- Sample:

      defaultpartition: main
      partition-main: /var/spool/cyrus
      partition-am: /var/spool/cyrus-am
      partition-nz: /var/spool/cyrus-nz
      partition-shared: /var/spool/cyrus-shared
      metapartition_files: header index cache expunge squat annotations
      metapartition-main: /var/spool/cyrusmeta/main
      metapartition-am: /var/spool/cyrusmeta/am
      metapartition-nz: /var/spool/cyrusmeta/nz
      metapartition-shared: /var/spool/cyrusmeta/shared
      search_engine: xapian
      search_index_headers: no
      search_batchsize: 8192
      defaultsearchtier: temp
      tempsearchpartition-main: /var/spool/search/main
      tempsearchpartition-am: /var/spool/search/am
      tempsearchpartition-nz: /var/spool/search/nz
      tempsearchpartition-shared: /var/spool/search/shared

These settings are in imapd.conf(5):

> `searchpartition-name:` <none>

> > The pathname where to store the xapian search indexes of searchtier for mailboxes of partition name. This must be configured for the defaultsearchtier and any additional search tier (see squatter for details).

> > For example: if defaultpartition is defined as part1 and defaultsearchtier as tier1 then the configuration must contain an entry tier1searchpartition-part1 that defines the path where to store this tier1’s search index for the part1 partition.

> > This option MUST be specified for xapian search.