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#1 (**permalink**) 02-28-2008, 08:33 AM

I'd like to write CGI-BIN compiled 'C' programs that use the MySQL 'C' API.

However, I'm concerned about dying processes. If a process segfaults or
otherwise dies unexpectedly:

a)Does the MySQL connection close automatically?

b)Do table locks release automatically?

Thanks, Dave.

#2 (**permalink**) 02-28-2008, 08:33 AM

"David T. Ashley" <dta@e3ft.com> wrote:
> I'd like to write CGI-BIN compiled 'C' programs that use the MySQL 'C' API.
>
> However, I'm concerned about dying processes. If a process segfaults or
> otherwise dies unexpectedly:
>
> a)Does the MySQL connection close automatically?
>
> b)Do table locks release automatically?

Table locks are released automatically if the connection terminates.

A client connection will be terminated by the following events:

1. when the client closes the connection explicitly
2. when the TCP connection to the server is closed
3. after connect_timeout seconds without any client action
(connect_timeout is configurable in my.cnf, default: 12 hours)
4. when somebody explicitly kills the thread in the MySQL server

In *most* cases the operating system will close the TCP connection(s)
for dying processes. In fact I haven't witnessed other behaviour.
But this may be pure luck.

XL
--
Axel Schwenke, Senior Software Developer, MySQL AB

Online User Manual: http://dev.mysql.com/doc/refman/5.0/en/
MySQL User Forums: http://forums.mysql.com/

#3 (**permalink**) 02-28-2008, 08:34 AM

"Axel Schwenke" <axel.schwenke@gmx.de> wrote in message
news:gjt7je.ulj.ln@xl.homelinux.org...
>
> Table locks are released automatically if the connection terminates.
>
> A client connection will be terminated by the following events:
>
> 1. when the client closes the connection explicitly
> 2. when the TCP connection to the server is closed
> 3. after connect_timeout seconds without any client action
> (connect_timeout is configurable in my.cnf, default: 12 hours)
> 4. when somebody explicitly kills the thread in the MySQL server
>
> In *most* cases the operating system will close the TCP connection(s)
> for dying processes. In fact I haven't witnessed other behaviour.
> But this may be pure luck.

Thanks.

My experimentation seems to hint at the same behavior.

Just one more question ...

In reading the MySQL documentation, it isn't clear to me what the difference
between the standard library and the "embedded" library are.

<BEGIN QUESTION>
What is the "embedded" library?
<END QUESTION>

An "embedded" (no server) library would seem to be impossible because only
the MySQL daemon can get at the MySQL database files involved.

I'm thinking the standard library is what I want because if the process
dies, the TCP connection closes, and the MySQL daemon cleans up everything.

Thanks.

#4 (**permalink**) 02-28-2008, 08:34 AM

"David T. Ashley" <dta@e3ft.com> wrote:

> In reading the MySQL documentation, it isn't clear to me what the difference
> between the standard library and the "embedded" library are.
>
> <BEGIN QUESTION>
> What is the "embedded" library?
> <END QUESTION>

I guess you mean the embedded server. This is the MySQL server in form
of a library. You link you programm against libmysqld. Soon after your
program starts, you call mysql_server_init() to start the embedded
server (running as subthread of your program now). You can access this
embedded server just like the external server (the API functions are
overloaded in libmysqld).

However this does not work if you have several instances of your
program running at the same time; i.e. if your program is a CGI app.

XL
--
Axel Schwenke, Senior Software Developer, MySQL AB

Online User Manual: http://dev.mysql.com/doc/refman/5.0/en/
MySQL User Forums: http://forums.mysql.com/

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C-Language MySQL API and Dying Processes