RE: Complete server lock

[Daniel]

MySQL and DNS can be such a fun issue because it comes
suddenly and leaves just as suddenly with --skip-name-resolve.

For in-depth info on how MySQL uses DNS, and info about
this potential DNS-related bug: http://codenode.com/mysql/dns

-Daniel

-Original Message-
From: Ben Clewett [mailto:[EMAIL PROTECTED] 
Sent: Friday, July 29, 2005 8:59 AM
To: JamesDR
Cc: mysql@lists.mysql.com
Subject: Re: Complete server lock



JamesDR wrote:
> I noticed, on my Linux server, that MySQL makes a DNS lookup anyway.
> Even if the IP is used or not. It normally digs on the PTR record. I
had 
> all of my perms IP based, however, it still looked at the PTR record.
At 
> the time I hadn't set any up in my DNS server. After I added all the
PTR 
> records of the clients that were connecting to the server, it was fast

> again.
> 
> ...Something to think about...

James, I think you've found the problem.  For the benefit of us novices,

what is the PTR record?  After which I can add this to my /etc/hosts, 
which should help.

If there is anybody who knows how to build a DNS clean MySQL, I would be

very interested in knowing.

Regards,

Ben Clewett.


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Re: Complete server lock

[Ben Clewett]

Michael,

Thank for the reference.  This is useful.

Ben.

Michael Stassen wrote:

Ben Clewett wrote:


JamesDR wrote:

I noticed, on my Linux server, that MySQL makes a DNS lookup anyway. 
Even if the IP is used or not. It normally digs on the PTR record. I 
had all of my perms IP based, however, it still looked at the PTR 
record. At the time I hadn't set any up in my DNS server. After I 
added all the PTR records of the clients that were connecting to the 
server, it was fast again.


...Something to think about...




James, I think you've found the problem.  For the benefit of us 
novices, what is the PTR record?  After which I can add this to my 
/etc/hosts, which should help.


If there is anybody who knows how to build a DNS clean MySQL, I would 
be very interested in knowing.


Regards,

Ben Clewett.



 From the manual , "You can 
disable DNS hostname lookups by starting mysqld with the 
--skip-name-resolve option. However, in this case, you can use only IP 
numbers in the MySQL grant tables."






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Re: Complete server lock

[Michael Stassen]

Ben Clewett wrote:


JamesDR wrote:

I noticed, on my Linux server, that MySQL makes a DNS lookup anyway. 
Even if the IP is used or not. It normally digs on the PTR record. I 
had all of my perms IP based, however, it still looked at the PTR 
record. At the time I hadn't set any up in my DNS server. After I 
added all the PTR records of the clients that were connecting to the 
server, it was fast again.


...Something to think about...



James, I think you've found the problem.  For the benefit of us novices, 
what is the PTR record?  After which I can add this to my /etc/hosts, 
which should help.


If there is anybody who knows how to build a DNS clean MySQL, I would be 
very interested in knowing.


Regards,

Ben Clewett.


From the manual , "You can 
disable DNS hostname lookups by starting mysqld with the --skip-name-resolve 
option. However, in this case, you can use only IP numbers in the MySQL grant 
tables."



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Re: Complete server lock

[Ben Clewett]

JamesDR wrote:
I noticed, on my Linux server, that MySQL makes a DNS lookup anyway. 
Even if the IP is used or not. It normally digs on the PTR record. I had 
all of my perms IP based, however, it still looked at the PTR record. At 
the time I hadn't set any up in my DNS server. After I added all the PTR 
records of the clients that were connecting to the server, it was fast 
again.


...Something to think about...


James, I think you've found the problem.  For the benefit of us novices, 
what is the PTR record?  After which I can add this to my /etc/hosts, 
which should help.


If there is anybody who knows how to build a DNS clean MySQL, I would be 
very interested in knowing.


Regards,

Ben Clewett.


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Re: Complete server lock

[JamesDR]

Ben Clewett wrote:

Jigal,

Thanks.

I can confirm that there were no domains used for our permissions.  All 
IP based.  Although this may have been the cause, I don't think it was 
in this case.  I think as well that DNS timeouts are in the region of 20 
seconds to 2 minutes.


Would any person know if there is any other part of MySQL which uses DNS 
lookups?  For instance, logging of some kind?


Or any other reason a MySQL daemon would not respond to a kill?

Thank for the ideas,

Ben Clewett.


Jigal van Hemert wrote:


Ben Clewett wrote:

It had been suggested that our DNS failed prior to this event.  I 
don't think MySQL uses DNS, but I am not entirely sure.




If the db, user, etc. tables in the mysql system database (containing 
privileges, etc.) contain host names instead of IP-addresses I suspect 
it needs a DNS to resolve these...


If I get a state where a 'kill' will not cause MySQL to exit.  Is 
there any other know way to ask MySQL to exit cleanly?




MySQL server was probably waiting for a bunch of DNS requests? Until a 
timeout occurs it will probably keep the connection waiting. This can 
cause a lot of connections to occur until you reach max_connections at 
which point it will not accept new connections anymore.


Regards, Jigal.




I noticed, on my Linux server, that MySQL makes a DNS lookup anyway. 
Even if the IP is used or not. It normally digs on the PTR record. I had 
all of my perms IP based, however, it still looked at the PTR record. At 
the time I hadn't set any up in my DNS server. After I added all the PTR 
records of the clients that were connecting to the server, it was fast 
again.


...Something to think about...

--
Thanks,
James

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Re: Complete server lock

[Ben Clewett]

Jigal,

Thanks.

I can confirm that there were no domains used for our permissions.  All 
IP based.  Although this may have been the cause, I don't think it was 
in this case.  I think as well that DNS timeouts are in the region of 20 
seconds to 2 minutes.


Would any person know if there is any other part of MySQL which uses DNS 
lookups?  For instance, logging of some kind?


Or any other reason a MySQL daemon would not respond to a kill?

Thank for the ideas,

Ben Clewett.


Jigal van Hemert wrote:

Ben Clewett wrote:

It had been suggested that our DNS failed prior to this event.  I 
don't think MySQL uses DNS, but I am not entirely sure.



If the db, user, etc. tables in the mysql system database (containing 
privileges, etc.) contain host names instead of IP-addresses I suspect 
it needs a DNS to resolve these...


If I get a state where a 'kill' will not cause MySQL to exit.  Is 
there any other know way to ask MySQL to exit cleanly?



MySQL server was probably waiting for a bunch of DNS requests? Until a 
timeout occurs it will probably keep the connection waiting. This can 
cause a lot of connections to occur until you reach max_connections at 
which point it will not accept new connections anymore.


Regards, Jigal.




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Re: Complete server lock

[Jigal van Hemert]

Ben Clewett wrote:
It had been suggested that our DNS failed prior to this event.  I don't 
think MySQL uses DNS, but I am not entirely sure.


If the db, user, etc. tables in the mysql system database (containing 
privileges, etc.) contain host names instead of IP-addresses I suspect 
it needs a DNS to resolve these...


If I get a state where a 'kill' will not cause MySQL to exit.  Is there 
any other know way to ask MySQL to exit cleanly?


MySQL server was probably waiting for a bunch of DNS requests? Until a 
timeout occurs it will probably keep the connection waiting. This can 
cause a lot of connections to occur until you reach max_connections at 
which point it will not accept new connections anymore.


Regards, Jigal.

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