[Dovecot] out of memory on dovecot alpha5

[Pavel Volkovitskiy]

Hello

Once a day i have these errors in doveecot.log:
===========================================
dovecot: Dec 16 14:06:04 Error: auth-worker(default): .Out of memory 
(Needed 52 bytes)
dovecot: Dec 16 14:06:04 Error: auth-worker(default): sql(login,<ip>): 
Password query failed: MySQL
 client ran out of memory
dovecot: Dec 16 14:06:06 Info: imap-login: Disconnected: user=<login>, 
method=PLAIN, rip=<ip>, lip=<ip2>
dovecot: Dec 16 14:06:06 Error: auth-worker(default): 
pool_system_malloc(): Out of memory
dovecot: Dec 16 14:06:06 Error: child 23022 (auth-worker) returned error 
83 (Out of memory)
============================================

And after that nobody can login

I do /etc/init.d/dovecot restart
and then it's working for a day

Before upgrade to alpha5 i was used 0.99.x series without eny errros on 
this server

What can i do to debug this?

-- 
Pavel