Hi,
There is a test that I am doing with FreeBSD and Linux. This test involves
qmail and postfix comparison. Both FreeBSD and Linux seems to have 1024 File
Descriptor limit. (FD_SETSIZE in select.h in FreeBSD) .
To have a better concurrency in qmail on smtp level. I have used a patch named
big-todo patch also used big-concurrency patch. These patches helps me to
increase concurrency in operating system. I set concurrent connection to
500(tcpserver -c 500). There is no problem until around 400-500 active smtp
connection. But if the total smtp connection exceeds 500, load average
increases to ~40-50 but cpu system time arises to %50-60. The strange issue is
that, this load increases when the connection is limited to accept 500
connections but the tool I use is configured to 700 (more than 500)
connections. Normally ucspi-tcp software limits connection to 500 ( -c 500) I
suspect it is something to do with Operating system level.
Additionally I have also patched FreeBSD kernel with 4096 FD_SETSIZE in
select.h in kernel and booted with that kernel. I have also compiled qmail from
scratch to accept 2040 connections (in conf-spawn) but there is no change I
mean I still can't get more than decent 500 connections with acceptable load
average.
I have also used postfix on both Linux FreeBSD:
default_process_limit = 500
smtpd_client_connection_count_limit = 500
but I still get strange load when connection raises more than 500
I suspect something is missing or need to be configured on the operating system
level (both Linux and FreeBSD)
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