Re: Connections with bad DNS cause lockups

[Gleb Paharenko]

Hello.


To make the suggestions, we should have enough amount of information.
If your MySQL server isn't heavy loaded, create a trace file and find
out the place where the new connections hang. See:
  http://dev.mysql.com/doc/mysql/en/making-trace-files.html



Tuc at T-B-O-H <ml@stripped> wrote:
>> 
>> Hello.
>> 
>> In my opinion, we're a little kinked in this issue. Let's start over.
>>
>        :( Sorry. I've been told by the GF that I have a habit of
> doing it to her too. 
>>
>> In one of your posts you mentioned that the server runs lots
>> of other services besides the database. 
>>
>        Yes, according to my runbook, the server :
> 
>        1) Is an NFS server to 4 other servers for web traffic
> and logging. 
>        2) Is the primary MX server for 7 domains (About 100
> emails a day)
>        3) Runs a Listproc for 4 mailing lists (About 5 messages
> a day to 60 people)
>        4) Runs MySQL (Approx 98 queries per hour)
>        5) Runs Seti@Home (2 processes)
>        6) Runs an IMAP Server for 1 user who logs on 5-10 
> minutes a day
> 
>        The server pushes about 120kb/s a second 
> according to MRTG for all that.
>>
>> Why do you think that
>> the cause of the server's weird behavior is MySQL?
>>
>        Maybe I wasn't clear about it. The server is running
> perfectly. I'm running SETI on it since its normally bored out
> of its ever loving mind. When someone with a missing or bad
> reverse DNS (PTR) record attempts to connect to the MySQL
> server, any other connection via either the socket or the
> TCP socket ends up blocking and waiting. Every other service
> on the machine is fine, but MySQL becomes completely
> unresponsive. When I said "DOS", I meant only against MySQL.
> The rest of the machine is fine to process anything it wants.
>>
>> Is server still
>> working, but you are unable to reach it through the network, or it
>> is completely hung?
>>
>        No other services are affected, only attempts to connect
> to MySQL via the socket or TCP. This makes what little access there
> is to the database (A searchable orchid database) stop, and monitoring
> detects it down and pages out. 
> 
> 
>                Thanks, Tuc 
>> 
>> >> 
>> >> 
>> >        So if thats the way (FreeBSD ports), then besides the already
> suggested
>> > changing to pure IP, is there any other ways to stop the DOS?
>> > 
>> >                Thanks, Tuc
>> > 
>> 
>> 
>> 

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