Will the Java JRE close database connections if an applications crashes or exits without closing its active connections? If not is it the responsibility of the database to time out these connections?
I understand that if Java crashes then the database will need to time out all open connections as there is nothing else to do the job.
EDIT
Additional thought. If a WAR deployed in Tomcat crashes, will the Tomcat server cleanup the open connections?
That really depends.
If your JRE itself crashes, it might not be able to close all the connections. If just your application crashes, it might be able to close connections when it frees the resources. This seems to be the case most of the time, in my experience, as long as the JRE itself does not die. The best defence is of course proper error handling and making sure you do not have more connections open than required.
From my experience, it's better to set up a data source in Tomcat, that way, even if your application crashes, it's not an issue with open resources. I'm a rather big fan of making my application server handle as much resource management as possible, that way I am protected a bit more from my sometimes adventurous code.
Most times your application should close the connections in any proper errorhandlers. I prefer to set up the data source in Tomcat, like Ewald mentioned. There you can define a maximum of connections, and a timeout in your context.xml. When your application stacks too much connections it will release it.
Related
We have a MVC 3 application which has been deployed onto a newly built Windows 2008 R2 Web Edition server which is performing badly.
This application has been through development, quality assurance and user acceptance testing cycles on the same operating system (different boxes) with no performance issues.
The only difference we can see with the server is that it sits in the DMZ and as such has two network adapters configured, one for the internet, and one to punch through the firewall.
We have put all sorts of logging into the application and confirmed that up until the 'return ActionResult' everything is working correctly (ie ~500ms). It then takes 15 seconds to render the page.
We have tried turning on debug=false in the config file, i'm not sure what else to look for here, it seems like an environment issue.
Any suggestions please ? I am about to investigate if the thread pool size could be causing problems.
Also, if it helps the page is using multiple partial views, i have read others having problems with them.
Thanks,
Matt
Since the application performs ok in other environments I would suggest you investigate following:
Database - are you running against different database? How long the queries execute? If you have non-optimized database with million records on production, and only few records in test you want find performance problems soon enough.
Network - what is the latency between web box and database? If you loose 100ms for each database query just because of network than if your page triggers 50 queries you've lost 5secs. I've seen poorly configured routers / load balancers that were doing just that.
Try profiling each component of your system (db, network, web box) in order to find out where you're wasting all that time. Try http://code.google.com/p/mvc-mini-profiler/.
PS. You MUST have debug=false in your prod env.
I have a rails app which is now hosted on dedicated server. Today something happened: app doesn't respond and I have no ssh access, restarting doesn't help and I am waiting for tech support to respond. But this is not a question, I just need this app to be online even if server fails. Which is the easiest option? Can I create second server on different hosting and serve from there in case of failure, if so, how to sync db and files? Application is not heavily loaded, I just need it to be available.
Difficult problem to solve. There's no one proven way to make this happen, but in general you need "No Single Point of Failure"
There's an entire science devoted to reliability in web applications -- no way can you get that answered in a SO question.
You can take frequent backups of your database, store them on S3 (and/or somewhere else). You can then
have an image of your applications server at your host
spin it up when your server dies
restore the database
Have the new application server take over responsibility (easiest way: assume the old server's IP address)
I have written several services in Delphi now, but I want to add the facility of auto updating the service either from a LAN unc path or from a http server. I have been pondering this and I am interested to hear peoples ideas. I can create a thread that will check for the update periodically, but how do I go about stopping the service uninstalling and installing automatically. My initial thoughts where to write a console app to do this and start it using create process, then let the service stop and the console app do the work, starting the new version of the service before it exits. Is this a good stratergy or shoul I consider something else. Thanks in advance
I do as you suggest. A thread checks occasionally for an update. If it is present, it downloads it and puts it into an appropriate place. It then verifies that it is wholesome (don't want it to be broken!). Finally, the thread then launches another app with parameters to tell it what to do, specifically, the name of the service, the location of the file to replace, and the file to replace it with. Then the service just waits.
When the updater app starts, it pauses a moment to make sure that the service is all stable, and then it uses the service control API to stop the service. It then monitors it until it is gone. Finally, it pauses a little to ensure that Windows has really finished with the file. Then it starts the process of renaming the old file to move it out of the way (if still in use, it retries a few times), and then copying the new file into place. And finally, it starts the service up again. Then the updater quits.
This has worked quite reliably for my services, and also standalone apps too (with different parameters for the updater app to know which mode). And if you are careful, you can update the updater using the exact same system, which is nice to watch.
I would have the service be a shell that only updates another executable or DLL file where the real code is at.
Have some communication method between the shell and the child process to force a shutdown and then have the shell perform the upgrade and relaunch the child.
As a side note, this makes debugging the service much easier as well as you'll be able to run the child process directly without having to worry about the extra efforts required to debug windows services.
your idea seems very good to me, however take this into consideration aswell:
- add module(the main core) to the service that will be unloaded and will load the updated module(*.dll file) when an update is available -- in this time the service should put the "tasks" in a queue or something...
additionally you can use plugins and/or scripts like Pascal script or DWScript
Last versions of Windows (I think since windows 10) does not allow a service to start other programs. So you will need an other program to run the update. It could be an other service.
Windows Services cannot start additional applications because they are
not running in the context of any particular user. Unlike regular
Windows applications, services are now run in an isolated session and
are prohibited from interacting with a user or the desktop.
I have a website that is hanging every 5 or 10 requests. When it works, it works fast, but if you leave the browser sit for a couple minutes and then click a link, it just hangs without responding. The user has to push refresh a few times in the browser and then it runs fast again.
I'm running .NET 3.5, ASP.NET MVC 1.0 on IIS 7.0 (Windows Server 2008). The web app connects to a SQLServer 2005 DB that is running locally on the same instance. The DB has about 300 Megs of RAM and the rest is free for web requests I presume.
It's hosted on GoGrid's cloud servers, and this instance has 1GB of RAM and 1 Core. I realize that's not much, but currently I'm the only one using the site, and I still receive these hangs.
I know it's a difficult thing to troubleshoot, but I was hoping that someone could point me in the right direction as to possible IIS configuration problems, or what the "rough" average hardware requirements would be using these technologies per 1000 users, etc. Maybe for a webserver the minimum I should have is 2 cores so that if it's busy you still get a response. Or maybe the slashdot people are right and I'm an idiot for using Windows period, lol. In my experience though, it's usually MY algorithm/configuration error and not the underlying technology's fault.
Any insights are appreciated.
What diagnistics are available to you? Can you tell what happens when the user first hits the button? Does your application see that request, and then take ages to process it, or is there a delay and then your app gets going and works as quickly as ever? Or does that first request just get lost completely?
My guess is that there's some kind of paging going on, I beleive that Windows tends to have a habit of putting non-recently used apps out of the way and then paging them back in. Is that happening to your app, or the DB, or both?
As an experiment - what happens if you have a sneekly little "howAreYou" page in your app. Does the tiniest possible amount of work, such as getting a use count from the db and displaying it. Have a little monitor client hit that page every minute or so. Measure Performance over time. Spikes? Consistency? Does the very presence of activity maintain your applicaition's presence and prevent paging?
Another idea: do you rely on any caching? Do you have any kind of aging on that cache?
Your application pool may be shutting down because of inactivity. There is an Idle Time-out setting per pool, in minutes (it's under the pool's Advanced Settings - Process Model). It will take some time for the application to start again once it shuts down.
Of course, it might just be the virtualization like others suggested, but this is worth a shot.
Is the site getting significant traffic? If so I'd look for poorly-optimized queries or queries that are being looped.
Your configuration sounds fine assuming your overall traffic is relatively low.
To many data base connections without being release?
Connecting some service/component that is causing timeout?
Bad resource release?
Network traffic?
Looping queries or in code logic?
I have a simple Rails app deployed on a 500 MB Slicehost VPN. I'm the only one who uses the app. When I run it on my laptop, it's fast enough. But the deployed version is insanely slow. It take 6 to 10 seconds to load the login screen.
I would like to find out why it's so slow. Is it my code? (Don't think so because it's much faster locally, but maybe.) Is it Slicehost's server being overloaded? Is it the Internet?
Can someone suggest a technique or set of steps I can take to help narrow down the cause of this problem?
Update:
Sorry forgot to mention. I'm running it under CentOS 5 using Phusion Passenger (AKA mod_rails or mod_rack).
If it is just slow on the first time you load it is probably because of passenger killing the process due to inactivity. I don't remember all the details but I do recall reading people who used cron jobs to keep at least one process alive to avoid this lag that can occur with passenger needed to reload the environment.
Edit: more details here
Specifically - pool idle time defaults to 2 minutes which means after two minutes of idling passenger would have to reload the environment to serve the next request.
First, find out if there's a particularly slow response from the server. Use Firefox and the Firebug plugin to see how long each component (including JavaScript and graphics) takes to download. Assuming the main page itself is what is taking all the time, you can start profiling the application. You'll need to find a good profiler, and as I don't actually work in Ruby on Rails, I can't suggest any: google "profile ruby on rails" for some options.
As YenTheFirst points out, the server software and config you're using may contribute to a slowdown, but A) slicehost doesn't choose that, you do, as Slicehost just provides very raw server "slices" that you can treat as dedicated machines. B) you're unlikely to see a script that runs instantly suddenly take 6 seconds just because it's running as CGI. Something else must be going on. Check how much RAM you're using: have you gone into swap? Is the login slow only the first time it's hit indicating some startup issue, or is it always that slow? Is static content served slow? That'd tend to mean some network issue (either on the Slicehost side, or your local network) is slowing things down, assuming you're not in swap.
When you say "fast enough" you're being vague: does the laptop version take 1 second to the Slicehost 6? That wouldn't be entirely surprising, if the laptop is decent: after all, the reason slices are cheap is because they're a fraction of a full server. You're using probably 1/32 of an 8 core machine at Slicehost, as opposed to both cores of a modern laptop. The Slicehost cores are quick, but your laptop could be a screamer compared to 1/4 of core. :)
Try to pint point where the slowness lies
1/ application is slow, or infrastructure (network + web server)
put a static file on your web server, and access it through your browser
2/ If it is fast, it is probable a problem with application + server configuration.
database access is slow
try a page with a simpel loop: is it slow?
3/ If it slow, it is probably your infrastructure. You can check:
bad network connection: do a packet capture (with Wireshark for example) and look for retransmissions, duplicate packets, etc.
DNS resolution is slow?
server is misconfigured?
etc.
What is Slicehost using to serve it?
Fast options are things like: Mongrel, or apache's mod_rails (also called passenger phusion or
something like that)
These are dedicated servers (or plugins to servers) which run an instance of your rails app.
If your host isn't using that, then it's probably defaulting to CGI. Rails comes with a simple CGI script that will serve the page, but it reloads the app for every page.
(edit: I suspect that this is the most likely case, that your app is running off of the CGI in /webapp_directory/public/dispatch.cgi, which would explain the slowness. This tends to be a default deployment on many hosts, since it doesn't require extra configuration on their part, but it doesn't give good performance)
If your host supports "Fast CGI", rails supports that too. Fast CGI will open a CGI session, and keep it open for multiple pages, so you get much better performance, but it's not nearly as good as Mongrel or mod_rails.
Secondly, is it in 'production' or 'development' mode? The easy way to tell is to go to a page in your app that gives an error. If it shows you a stack trace, it's in development mode, which is slower than production mode. Mongrel and mod_rails have startup options to determine whether to run the app in production or development mode.
Finally, if your database is slow for whatever reason, that will be a big bottleneck as well. If you do have a good deployment (Mongrel/mod_rails/etc.) in production mode, try looking into that.
Do you have a lot of data in your DB? I would double check that you have indexed all the appropriate columns- because this can make a huge difference. On your local dev system, you probably have a lot more memory than on your 500 mb slice, which would result in the DB running a lot slower if you have big, un indexed tables. You can also run the slow queries logger in MySql to pinpoint columns without indexes.
Other than that, yes- passenger will need to spool up a process for you if you have not been using the site recently. If this is the case, you should see a significant speed increase on second, and especially third and later page loads.
You might want to run a local virtual machine with 500 MB. Are you doing a lot of client-server interaction? Delays over the WAN are significant
You might want to check out RPM (there's a free "lite" version too) and/or New Relic's Tune Up.
Your CPU time is guaranteed by Slicehost using the Xen virtualization system, so it's not that. Don't have the other answers for you, sorry! Might try 'top' on a console while you're trying to access the page.
If you are using FireFox and doing localhost testing (or maybe even on LAN) you may want to try editing the network.dns.disableIPv6 setting.
Type about:config in the address bar and filter for network.dns.disableIPv6 and double-click to set to true.
This bug has been reported mainly from Vista OS's, but some others as well.
You could try running 'top' when you SSH in to see which process is heavy. If you also have problems logging you, perhaps you may try getting Statistics in the Slicehost manager.
If you discover it is MySQL's fault, consider decreasing the number of servers it can spawn.
512 seems decent for Rails application, you might have to check if you misconfigured too.