Author: Paul Fisher Date: To: Jeremy Harris CC: exim-dev Subject: Re: [exim-dev] [Bug 1292] New: Add option to back DKIM -K temp
files to POSIX shared memory
On 09/04/2012 03:39 PM, Jeremy Harris wrote: > Any performance numbers?
The change, by itself, shouldn't have a significant performance impact
for a reasonably sized Exim system. The main purpose of the change was
to shunt -K files off to tmpfs, so there's one less variable to
consider for performance tuning the spool filesystem.
Assuming no TLS, the outgoing path is roughly:
-H + -D (disk) -> -K (memory) -> DKIM header + sendfile -K (socket)
It would be interesting to see what benefits could be gained by
switching -D to be an SMTP on-the-wire representation of the data
portion. That would allow use of sendfile/splice further up the
outbound processing stack, DKIM signing could switch over to using
mmap, and there are perhaps optimizations for the inbound path in the
case of receiving SMTP data, queuing + header changes, and then
shipping the same data portion back out over SMTP.
