From: Dave Crooke <dcrooke@gmail.com>
To: Craig Ringer <craig@postnewspapers.com.au>
Cc: Dmitri Girski <mitek17@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: pg_connect takes 3.0 seconds
Date: Thu, 7 Jan 2010 14:13:08 -0600
Message-ID: <ca24673e1001071213y57e6fd73q757bffd98ef39baa@mail.gmail.com> (raw)
In-Reply-To: <4B458FD0.8020205@postnewspapers.com.au>
References: <daed64561001041812s602a3098l686f630d6448835f@mail.gmail.com>
<daed64561001061844q528adafeke89b78adb868b15a@mail.gmail.com>
<4B458FD0.8020205@postnewspapers.com.au>
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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To: pgsql-performance@postgresql.org
Cc: dcrooke@gmail.com, craig@postnewspapers.com.au, mitek17@gmail.com
Subject: Re: pg_connect takes 3.0 seconds
In-Reply-To: <ca24673e1001071213y57e6fd73q757bffd98ef39baa@mail.gmail.com>
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