[Dovecot] dovecot, mdbox and indexes

[Angel L. Mateo]

El 30/06/11 15:53, William Blunn escribió:
> On 30/06/2011 13:28, Angel L. Mateo wrote:
>> We are now trying to migrate to the third scenario and using mdbox.
>>
>> These errors cause a corrupted index and we have to manually delete
>> the user's index so he could read his mail again.
>>
>> * I connect then to a server that have no index for me. The only
>> problem is that the previously deleted mail appears again.
>> * I connect then to a server with an outdated index: this is the
>> problem. I have only the messages in that outdated index. The mail
>> received since then has disappeared (although I could receive new mail).
>>
>> How could I solve this problem? Is this really a problem? Should I use
>> a shared storage for indexes? What is the best configuration for a
>> high availability service?
>>
>
> !!!!! DANGER, DANGER !!!!!!
>
> Under mdbox, the so-called "indexes" are not indexes in the traditional
> (database) sense of the word (a file maintained alongside the main data
> file which is used to speed up access to the main file, and can be
> regenerated at will), but rather are (binary) database files which
> contain crucial metadata which is not held anywhere else.
>
> These filed cannot be regenerated at will.
>
> For example:
>
> The so-called "map index" (message store database) contains a (flat)
> list of all messages in a (user's) mailstore together with their
> reference counts, which storage file they're stored in.
>
> The "folder index" (folder message metadata database) in each folder
> directory contains a list of the message numbers which are "in" that
> folder. Those message numbers identify a particular message in the
> message store database, which identify a particular m.* storage file,
> and where within that file the message is.
>
> Lose these files, and you destroy the information about:
> * which message is supposed to be in which folder,
> * which messages are supposed to be deleted and which aren't, and
> * all message keywords.
>
> Under mdbox, losing these files buggerises the mailstore.
>
> You may wish to read http://wiki2.dovecot.org/MailboxFormat/dbox
>
> "... with dbox the Index files actually contain significant data which
> is held nowhere else. Index files for both *single-dbox* and
> *multi-dbox* contain message flags and keywords. For *multi-dbox*, the
> index file also contains the map_uids which link (via the "map index")
> to the actual message data. This data cannot be automatically recreated,
> so it is important that Index files are treated with the same care as
> message data files."
>
	I know this. That was my question. So, what is the best configuration 
for a high availabilty environment. An active/passive cluster?