 | | | Subject: Re: Issues with multi-queries | Subject: Re: Issues with multi-queries 2007-11-07 - By Paul Martin
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My point is not to debug my own code, but figure out why the server keeps
dropping the connection. I have been looking at the user manual and will
adopt the templates for some of my calls in the near future. I can also
make use of the transaction class, sure, change the getch (only a simple way
to exit the program). The con object is made global and the local one I
removed. The endl's are used because the original multiquery example used
them.
I've just modified a simple example to show it break. This is the type of
table etc. that I am using... if the structure is wrong please point it out.
I suppose I could use the sample db but that might not behave the same.
What I NEED to know is why when I send a bunch of queries using multiquery
the connection gets dropped and needs to be re-initialized. I have a
feeling the engine isn't ready for another call for a short time, and
re-sending another one so quick catches it in a bad state. That is what the
Sleep calls try to show. Without them the connection is dropped almost
every time. So I believe there is a problem either in the engine or the C++
wrapper.
It looks like there may be a memory leak issue as well, but I'd like to
figure out the first problem first.
Paul
-- -- Original Message -- --
From: "Warren Young" <mysqlpp@(protected)>
To: "MySQL++ Mailing List" <plusplus@(protected)>
Sent: Wednesday, November 07, 2007 4:39 PM
Subject: Re: Issues with multi-queries
> Paul Martin wrote:
>>
>> Sleep function...
>
> It's a bad sign when your program needs to call Sleep() to function
> correctly. Race conditions galore lie down that path.
>
>> note that you must add a 'dbtest' database and a user called 'TestApp'
>> using 'password' with rights to that db.
>
> Why make us create a special database and user for you, when you can
> modify your example to do its work in the MySQL++ example database? If
> the problem goes away or changes when making that conversion, you've
> learned something that may point you to a fix.
>
>> cout << "Connection fried... ";
>> Sleep(10);
>
> Tiny little delays like this are particularly suspect.
>
>> try {
>> // Execute query and print all result sets
>> Result res = query.store();
>> res.purge();
>
> You don't need to call purge() yourself. It's a cleanup function within
> ResUse and Result. It's not going to be public any more in v3.
>
> I'm also concerned about whether you've elided code in this area: is there
> actual work done between the store() and purge() calls? Also, if you're
> using res after the purge call, Bad Things (TM) will happen.
>
>> query << "BEGIN WORK;" << endl;
>
> All these newlines are garbage to MySQL's query parser. Maybe it happens
> to ignore them in all cases that matter to you, or maybe they're part of
> the problem.
>
> Also, you should be using MySQL++'s Transaction class here for exception
> safety instead of rolling your own SQL. See section 3.9 in the user
> manual.
>
>> query << "SET FOREIGN_KEY_CHECKS=0;" << endl;
>> query << "DROP DATABASE IF EXISTS dbtest;" << endl;
>
> You do know you don't have to do these insertions in separate C++
> statements, right? This works fine:
>
> query << "BEGIN WORK;" <<
> "SET FOREIGN_KEY_CHECKS=0;" <<
> "DROP DATABASE IF EXISTS dbtest;" <<
> ...
> ;
>
>> query << "INSERT INTO Status
>> VALUES(1,29,2,1,'20071106111629','20071106111629',DEFAULT,180,0);" <<
>> endl;
>
> Any reason you're not using either template queries or SSQLS here? MySQL++
> will generate a lot of the most repetitive sorts of SQL for you, if you
> let it.
>
>> for(;;)
>> {
>> Query query = con.query();
>
> This is hiding a variable of the same name outside the loop. You could
> just be reset()ting the query object at the top of the loop instead.
>
>> // 105 more UPDATEs with similar data
>
> Why so many? I realize there's an overhead to each transaction, so the
> more transactions you batch up in each query execution the better, but the
> point of diminishing returns has to be well before this.
>
>> if(kbhit())
>> {
>> cout << "Program halted by user\n";
>>
>> while(kbhit())
>> char a=getch();
>> exit(0);
>> }
>> }
>
> Instead of this unportable DOS-era crappery, please consider this instead:
>
> string s;
> cin >> s;
>
> It's not "Press any key", but it suffices. I say this not just because of
> style reasons, but also because you're cutting off a big chunk of your
> testing audience if you stick to these Windowsisms.
>
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>
>
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