From: Dmitri Girski <mitek17@gmail.com>
To: Dave Crooke <dcrooke@gmail.com>
Cc: Craig Ringer <craig@postnewspapers.com.au>
Cc: pgsql-performance@postgresql.org
Subject: Re: pg_connect takes 3.0 seconds
Date: Sun, 10 Jan 2010 03:36:50 +1100
Message-ID: <daed64561001090836l2aadd92awb1e4413e3cf27066@mail.gmail.com> (raw)
In-Reply-To: <ca24673e1001071213y57e6fd73q757bffd98ef39baa@mail.gmail.com>
References: <daed64561001041812s602a3098l686f630d6448835f@mail.gmail.com>
<daed64561001061844q528adafeke89b78adb868b15a@mail.gmail.com>
<4B458FD0.8020205@postnewspapers.com.au>
<ca24673e1001071213y57e6fd73q757bffd98ef39baa@mail.gmail.com>
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@gmail.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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To: pgsql-performance@postgresql.org
Cc: mitek17@gmail.com, dcrooke@gmail.com, craig@postnewspapers.com.au
Subject: Re: pg_connect takes 3.0 seconds
In-Reply-To: <daed64561001090836l2aadd92awb1e4413e3cf27066@mail.gmail.com>
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