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Excessive DB connections. [message #613915] Tue, 13 May 2014 09:35
Roachcoach
Messages: 1510
Registered: May 2010
Location: UK
Senior Member
No, there are no ora errors here. It's not what you think!

Firstly and apologies up front for the video link, it explains it better than I.

Oracle Real World OLTP Performance Video

It's 11 minutes and gives context to my question/rant.

Time and again I am seeing database with horrendous connection management - there are FAR too many connections into the database.

99% of the time these sit idle and do nothing, then the application/middleware decides something, somewhere is "slow" and promptly tries go active with these connections thereby killing the database (and sometimes even the host). It only happens when the system is busy and manifests to the untrained eye as a "bad database" issue. The wait events are horrible - concurrency, mutexes, config. All that bad stuff you never usually see and you're tasked with "fixing". Unfortunately the fix is sorting out the application you dont own and cant control.

Of course the idea that a machine with 64-128 cores is able to simultaneously process a few thousand things at the same time is utter nonsense, but I'm singularly unable to get that message across - something not helped by the symptoms of this particular problem appearing DB side, app logs showing connections all maxed out and the DB going slow etc.


So - has anyone run into this in the past? How did you manage to convince people? I've sent the video onto various people but the trouble seems to be that I'm battling against everything these guys have ever known and it's never easy to be told you're just doing it wrong and the few who are willing to listen can't really do much about it.

Now then, what I'm hoping is that a) I'm not alone and b) people have found some decent sources/white papers I can quote from (videos aren't as snappy) as to why this is a terrible idea and the damage it can do. However my google isnt any use and the major issue I have here is convincing people that less connections can get through more work and it's (essentially) their fault that the databases are tipping over. It's posed to us that the DBs aren't scaling and that we somehow need to "fix" this.

Frankly it seems to be endemic to connection pools that they have far more than a system could ever support and to quote Graham Wood - It's just a big cannon pointed at the server waiting to kill you at the worst possible time - because this only ever happens when you're busy.


I've put this under server admin because it's the poor DBAs that get lumbered with it and we can't fix it. If mods feel its better under networking, fair play Smile
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