Re: pg_connect takes 3.0 seconds

Thanks for advice, Dave!

This saga ended in an unexpected way: the firewall died.
Since the replacement firewall installed I have not seen any 3 seconds
connects. Well, there was no real load so far, but I will keep checking.

Thanks to everyone replied, it was very helpful.

Cheers,
Dmitri.

On Fri, Jan 8, 2010 at 7:13 AM, Dave Crooke <dcrooke(at)gmail(dot)com> wrote:

> Oops, I meant to mention this too .... virtually all GigE and/or server
> class NICs do TCP checksum offload.
>
> Dimitri - it's unlikely that you have a hardware issue on the NIC, it's
> more likely to be a cable problem or network congestion. What you want to
> look for in the tcpdump capture is things like SYN retries.
>
> A good way to test for cable issues is to use a ping flood with a large
> packet size.
>
> Cheers
> Dave
>
> Hang on a sec. You need to ignore bad checksums on *outbound* packets,
>> because many (most?) Ethernet drivers implement some level of TCP
>> offloading, and this will result in packet sniffers seeing invalid checksums
>> for transmitted packets - the checksums haven't been generated by the NIC
>> yet.
>>
>> Unless you know for sure that your NIC doesn't do TSO, ignore bad
>> checksums on outbound packets from the local interface.
>>
>> --
>> Craig Ringer
>>
>>
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>

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