dovecot 2 low TCP speed (fetching big mail)

[Robert Blayzor]

On Dec 31, 2014, at 1:23 PM, Wojciech Puchar <wojtek at puchar.net> wrote:
> 
> i use dovecot 2 under FreeBSD (dovecot2-2.2.15 compiled from ports).
> 
> tried both with kqueue enabled or not.
> 
> everything works very fast, EXCEPT fetching big mail.
> 
> tried multiple clients (thunderbird on windows, alpine on the same server, alpine on other unix server connected by 1Gb/s LAN)  and fetching peaks at 1MB/s. NO SSL!
> 
> could you please point me where to search for a problem.
> 
> hints:
> 
> writing over IMAP (eg. writing to Sent folder) works at full speed.
> 
> Doesn't seem like a problem with unix server, every other service goes at speed 70-100MB/s both directions (like samba, ftp).
> 
> tried to turn off "kqueue" compile time option, no difference.
> 
> Please give me a hint at least what to check. Does dovecot use other way to sent data over TCP socket than other programs?


Beat metal or VM?  Which NIC driver?  IPv4 or IPv6?

Is the mail spool on the local server or on a SAN like NFS or ISCSI?

How slow is "slow" ?  How big is "big" ?  Does it stall?  Does it start of fast and slow down?


-Robert