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• How to store data on a machine whose power gets cut at random

  - by Sevas

  I have a virtual machine (Debian) running on a physical machine host. The virtual machine acts as a buffer for data that it frequently receives over the local network (the period for this data is 0.5s, so a fairly high throughput). Any data received is stored on the virtual machine and repeatedly forwarded to an external server over UDP. Once the external server acknowledges (over UDP) that it has received a data packet, the original data is deleted from the virtual machine and not sent to the external server again. The internet connection that connects the VM and the external server is unreliable, meaning it could be down for days at a time. The physical machine that hosts the VM gets its power cut several times per day at random. There is no way to tell when this is about to happen and it is not possible to add a UPS, a battery, or a similar solution to the system. Originally, the data was stored on a file-based HSQLDB database on the virtual machine. However, the frequent power cuts eventually cause the database script file to become corrupted (not at the file system level, i.e. it is readable, but HSQLDB can't make sense of it), which leads to my question: How should data be stored in an environment where power cuts can and do happen frequently? One option I can think of is using flat files, saving each packet of data as a file on the file system. This way if a file is corrupted due to loss of power, it can be ignored and the rest of the data remains intact. This poses a few issues however, mainly related to the amount of data likely being stored on the virtual machine. At 0.5s between each piece of data, 1,728,000 files will be generated in 10 days. This at least means using a file system with an increased number of inodes to store this data (the current file system setup ran out of inodes at ~250,000 messages and 30% disk space used). Also, it is hard (not impossible) to manage. Are there any other options? Are there database engines that run on Debian that would not get corrupted by power cuts? Also, what file system should be used for this? ext3 is what is used at the moment. The software that runs on the virtual machine is written using Java 6, so hopefully the solution would not be incompatible.

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• Why would an ext3 filsystem be rolled back on a Debian VM running in VirtualBox after loss of power to the host

  - by Sevas

  A Debian Virtual machine runs as a Guest VirtualBox VM. It's filesystem is EXT3. The host system loses power and after booting up the host system and guest VM, I find that the VM's filesystem has been rolled back to a previous state, losing changes made to the filesystem some time before losing power. The operations that were rolled back had been fully completed before the loss of power (files fully copied, file handles closed, etc.), but it's possible and even likely that other write operations were occuring on the VM at the point of the crash. So I am trying to figure out if it's the filesystem recovery process that rolls back filesystem operations after encountering corruption post power loss, or is it possibly related to VirtualBox and the way it ignores flush requests for performance gains by default (discussed here) Are there any other factors that would result in the filesystem being rolled back after losing power?

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• Configuring the fetch attempt duration when EHCache attempts to connect to a Terracotta server that

  - by Sevas

  Hey, if I try to connect to a Terracotta server that is currently down by calling net.sf.ehcache.CacheManager.create();, EHCache keeps retrying connection attempts for a full 300 seconds before throwing an exception with this message: Could not fetch configuration data from the server at 'terracottahost:9510'. Fetch attempt duration: 300 seconds. Is there any way to modify this time to be maybe 30 or 60 seconds? Thank you!

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• How to create an MSI package that installs no files and only executes some commands using Wix

  - by Sevas

  I am trying to create an MSI package that uses the AppCmd application to configure IIS7. It only has to execute some commands that call AppCmd. Some commands need to be called when installing, other commands need to be called when uninstalling. Here is what I have now: I have a property that points to AppCmd: <Property Id="APPCMD" Value="C:\Windows\system32\inetsrv\appcmd.exe" /> I have my custom actions: <CustomAction Id="UnlockHandlerSection" Return="check" Property="APPCMD" ExeCommand="unlock config /section:system.webServer/handlers" /> I have Custom elements that call the actions: <InstallExecuteSequence> <Custom Action="UnlockHandlerSection" After="InstallFiles">NOT Installed AND NOT PATCH</Custom> <InstallExecuteSequence> The problem with this is is that the commands are not called when I try to install the resulting MSI package. Could anyone please advise me on what I am doing wrong? Thank you!

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