Running multiple sync_clients

[Simon Matter]

> Bron Gondwana wrote:
>> On Thu, Nov 18, 2010 at 12:58:10PM -0500, Michael D. Sofka wrote:
>>> Is it safe to run multiple sync_clients?  Is there an advantage to
>>> doing so?
>>>
>>> I had to restart sync_client once.  After later restarting cyrus two
>>> sync_clients were running, and appeared to do well together.  Still, I
>>> stopped the old process out of caution.
>>
>> What version?  In 2.3.x, the sync_server will obtain a lock, so you can
>> only run one sync_server at a time.  This means the sync_clients will
>> take it in turns sending data.
>
> 2.3.16.  This description fits what I was seeing.
>
>
>> In 2.4, there is no global locking - just locks on each mailbox.  So
>> it's
>> possible for two sync_clients to run at the same time.  There is a
>> possibility this will lead to the same data being sent twice.  It won't
>> cause corruption, but it will cause excess IO!
>>
>> Are you sure it's actually two sync_client instances?  In every released
>> version, sync_client forks immediately upon starting and then forks
>> again
>> to actually send data.
>
> Yes.  There were a total of 4 sync processes.  Two parents, each with a
> child worker.  The logs showed two sync_client processes taking turns.
>
>> Which is a problem because it opens the BDB environment once and closes
>> it
>> many times.  So I've now changed it on my development branch to not fork
>> the second time, but just keep it all in once process.  We'll see if
>> there
>> are actually any memory leaks left!
>
> Another question I have is what are /var/lib/imap/db/*?  File says they
> are Berkeley dbs, but I thought all databases were skiplist in this
> release.  I can't find the configuration options associated with this

That's not true for 2.3.16. Some db's are still BDB by default in vanilla
2.3.16.

Simon