So I had occasion to post an email that contained a data file, about 1M in size, averaging maybe 15 bytes/line (it was basically e-mail addresses from an extract, one per line). I hit 'send', and I'm watching gkrellm report 300K/sec going out my cable connection to our mail hub.. and after 3 seconds it's not done sending. After a minute it's still blasting at 300K/sec. 6 minutes or so later, it finally finishes. I found this piece of info: http://www.imperialviolet.org/2010/06/25/overclocking-ssl.html "Packets and records SSL/TLS packages the bytes of the application protocol (HTTP in our case) into records. Each record has a signature and a header. Records are packed into packets and each packet has headers. The overhead of a record is typically 25 to 40 bytes (based on common ciphersuites) and the overhead of a packet is around 52 bytes. So it's vitally important not to send lots of small packets with small records in them. I don't want to be seen to be picking on Bank Of America, it's honestly just the first site that I tried, but looking at their packets in Wireshark, we see many small records, often sent in a single packet. A quick sample of the record sizes: 638 bytes, 1363, 15628, 69, 182, 34, 18, \u2026 This is often caused because OpenSSL will build a record from each call to SSL_write and the kernel, with Nagle disabled, will send out packets to minimise latency. This can be fixed with a couple of tricks: buffer in front of OpenSSL and don't make SSL_write calls with small amounts of data if you have more coming. Also, if code limitations mean that you are building small records in some cases, then use TCP_CORK to pack several of them into a packet." I do some back-of-envelope math, and even at each 15 byte line becoming a one-record packet, that's still 15+40+50 bytes - call it 100, or a factor of around 10. So what would have taken 3 seconds at line speed would take 30 seconds. But mine took around 6 minutes. Are we sending packets that have single 1-byte records in them? 1+40+50 is about the only way I can come up with the bloat factor that I'm seeing...
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