[Dovecot] Dovecot 2.0.1 Quota dict timeout

[David Jonas]

 Since an upgrade to 2.0.1 from 1.2.x we're seeing this on (mostly)
large mailboxes (Maildir)

Sep  4 11:27:25 dovecot: dict: mysql: Connected to 192.168.dd.dd (accounts)
...
Sep  4 11:27:46 kelly-a dovecot: lda(u1 at example.com):): msgid=<123 at xxx>:
saved mail to INBOX
Sep  4 11:27:47 dovecot: dict: Error: sql dict: commit failed: Not
connected to database
Sep  4 11:27:47 dovecot: imap(u1 at example.com): Error: dict quota: Quota
update failed, it's now desynced

The dict is MySQL on another server, same switch.  It does appear that
the quota gets out of sync. From the entries I checked an email is often
being delivered shortly before the error (as above). But I also see it
happen with the lda:

Sep  4 08:27:11 dovecot: pop3(u2 at example.com): Disconnected: Logged out...
Sep  4 08:42:48 dovecot: lda(u2 at example.com): msgid=<123 at aaa>: saved
mail to INBOX
Sep  4 08:43:26 dovecot: lda(u2 at example.com): msgid=<123 at bbb>: saved
mail to INBOX
Sep  4 08:43:26 dovecot: dict: Error: sql dict: commit failed: Not
connected to database
Sep  4 08:43:26 dovecot: lda(u2 at example.com): Error: dict quota: Quota
update failed, it's now desynced
Sep  4 08:46:14 dovecot: pop3-login: Login: user=<u2 at example.com>,...

This is happening on two different dovecot servers. The only thing they
share is the MySQL server, but it has a load of 0.5 at peak.

Is there something that can be tuned to keep this from happening?

Possibly relevant entries from `doveconf -n`. Any tuning regarding dict
can be assumed as default:

maildir_very_dirty_syncs = yes
mail_plugins = quota
plugin { quota = dict:user:%LTd-%LTn:proxy::quota }

Thanks!

David