[squid-users] Meaning of "HTTP I/O number of reads"

[Amos Jeffries]

On 26/08/2016 2:58 a.m., Peter Viskup wrote:
> Hello all,
> we do experience some connection issues with SFTP and clear HTTP
> clients on Squid 3.4 version built with SSL split.

What is this "SSL split" you speak of?

Squid does not support SFTP as far as I am aware except by CONNECT
tunnelling done by the client. Which is difficult since (S)FTP has
several TCP connections going in different directions at once.

> We occasionally see ERR_CONNECT_FAIL with SYSERR=110.

TCP connection setup failed. Whatever your operating system means by the
"110" message is the reason why.

> 
> Just discovered higher value of "HTTP I/O number of reads" at the time
> the issue occur.

If you mean the SNMP  OID *.1.3.1.2.0 (aka cacheSysNumReads). Which is
described as "HTTP I/O number of reads".

It is the counter of how many system read(2) I/O operations that have
been done for HTTP traffic. Being a counter, it will only ever go up.

> I am not able to understand this value - what it points to. Sometimes
> the value of HTTP I/O number of reads jump from tenths to 6000 or even
> higher.
> 


Since you imply that you are proxying CONNECT tunnels containing entire
SFTP transactions. It would be reasonable to expect a lot of read
operations to happen for them. Both the 'S' and the 'FTP' layers each
have a lot of small messages going back and forth through the tunnel.


You might also be having bug 2907. Which is fixed in Squid-3.5. Please
try an upgrade.

Amos