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Re: How do I handle a DB error when a SQL statement must not fail?

by sundialsvc4 (Abbot)
on Mar 31, 2014 at 13:46 UTC ( #1080397=note: print w/replies, xml ) Need Help??

in reply to How do I handle a DB error when a SQL statement must not fail?

I’m sure that there will very-shortly be some recommends from other people about what sort of service you might use ... but ... given what you have just said about the activity for this table in your most-recent post, great big bells are going off in my head right now to the effect that I can see no plausible reason why you should be encountering deadlocks in this situation, other than that there is an as-yet undiscovered bug in your program.   I would take a very close look at your SQL server's logs and/or administrative console.   There is something wrong with this picture.

If you are doing simple inserts of reasonable volumes of data, each one enclosed in a transaction with a reasonable isolation-level, and there is no other competing activity except at 1 AM, then I simply cannot fathom why you would ever be encountering deadlocks.   I was skeptical about this earlier, thinking it could be something else in a very-unusual situation, but now I’m sayin’ that line from Men In Black:   “Zed, we got a bug!”   Therefore, my advice to you now shifts back to considering what the bug might be – and I hope that other Monks will now chime-in on that, as I expect they will.

And, okay, you’ve really piqued my curiosity now.   What is it that your competitor takes twenty(!!) seconds (seconds, not microseconds) to do with a database?

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Re^2: How do I handle a DB error when a SQL statement must not fail?
by ted.byers (Monk) on Mar 31, 2014 at 19:26 UTC

    That, too, was my gut reaction, but the MySQL gurus I talked with suggested it may be a deadlock, so I started to test for that, as, not being a true expert with MySQL, I had no concrete evidence that it wasn't a deadlock.

    But, neither can I fathom what kind of bug can be in my code that would allow it to work 99.99% of the time, and give apparently random failures.

    I wonder if it is a question of resource exhaustion, as suggested here by Anonymous Monk on Mar 29, 2014 at 00:21 UTC. That is something I am presently investigating. I finally found a resource monitor that will log resource use to a file for CPU cycles, memory, disk IO and network traffic. And, I have beefed up the logging done by MySQL. Hopefully, between those logs, and whatever you and other monks suggest is worth examination regarding whatever kind of bug I may have, I will get to the bottom of this RSN.

    I am still interested in learning about these servers you mentioned (particularly FastCGI and XML::RPC, and how they can serialize insertions into a DB with reqeuests coming from multiple CGI processes, along with how much traffic will make such infrastructure mandatory

    As for what my competition is doing, I have no idea. I watch industry reports, particularly those that report average response times for services like mine, response time being measured as the time the client software makes a request to the time it gets a response time back. Being competitors, I doubt they'll let me look at their code or the architecture they use. ;-) Back when I developed desktop applications in Java and C++ (I preferred C++ because it was, and still is, blindingly fast relative to Java, or any other language I can use), I found in some cases, it was just a case of using a compiled language rather than an interpreted language, and in a great many more cases, it was a question of using the wrong algorithm to complete the task (e.g. using a linear search through an enormous dataset, rather than the more sensible binary search). Now, if I can learn how to use C++ to handle requests using FastCGI, and could have a good library to add FastCGI support to my C++ projects, then I may well resort to that, at least if and when the traffic grows to a point where Perl could have trouble handling it (or use profiling information to find out where the bottlenecks are, and see if a package written in C++ can improve things). In what ways my competitors make their systems so slow, I can make educated guesses, but can not really know because I can't see their code.

    BTW, perhaps you might had paraphrased Men in Black, rather than quoting it, to say, "Ted, We have a bug." ;-)



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