Firewall issues continue.
Once again if anyone had similar problem please help.
We did various tests and found out the following:
LIMIT 10 , 100, 1000 works fine. On 2000 it breaks. I checked queries
of different type against the same table and different tables. It
works the same with intermittent errors even on such simple commands
as 'show tables' (see below).
show tables;
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id:30
or
ERROR 2013 (HY000): Lost connection to MySQL server during query
There is absolutely nothing in the log or error log except last query
run.
The actual size of queries that break is not that big - 3000
records. It all works fine when the client is outside the firewall.
Also it does not matter if the database is on AIX or OS X. We see
same behavior on both.
We do see bad checksums on TCP dump and (as confirmed by Cisco) their
firewall sees all the interfaces coming into it as VLAN's , and thus
does VLAN tagging. VLAN tagging reduces the MTU size by about 20 to
30. That is the only difference we can determine so far.
Thanks,
Peter
On Oct 5, 2006, at 2:23 PM, Christian Hammers wrote:
Hello Peter
On 2006-10-05 Peter Gershkovich wrote:
Problem:
When we run a large query (returns 4000 records) on a firewalled
XServe (OS X 10.4) against Mysql database (outside firewall) on an
AIX (Version 5.2) machine the database server intermittently
generates the following errors:
ERROR 2006 (HY000): MySQL server has gone away
If the result is large, check if max_allowed_packet is set to at least
16MB or so in both, the client and the serve (see docs how to
configure
variables best).
Also, a gone away server normally means a crash of mysqld for which
some
debugging output is written on stderr by mysqld. In Debian Linux
this is
sent to syslog, check where your output has gone to.
Third, try experimenting if the same problem occurs if you use
LIMIT 10
or if the query takes a very long time *before* the output is sent
to the
client. That helps identifying which limit or timeout you've hit.
A firewall normally only lead to trouble if either the query takes
say 5min
before the first result row comes and the firewall things that the
connection is timed out or if you have an enormous number of
simultaneous
connections and some connection tracking table runs full.
bye,
-christian-
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Peter Gershkovich M.D.
Associate Research Scientist
Senior Manager, Information Technology
Yale University School of Medicine
Department of Pathology
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