Norbert, Answers are inline.
On Monday, April 15, 2013 8:29:34 AM Madarasz, Norbert wrote: > Hi all, > > This is the first time to write you. As part of my master's thesis at > Budapest University I should simulate the key functions of VCL with > CloudSim. > > For that the allocating logic is very important part means how a computer > is assigned to a reservation. I checked the cwiki page of VCL but the exact > procedure is not published. I've started to look inside the code and found > the predictive levels in PERL modules and it was understandable thanks to > vcld.log file which helped me to backtrace when, how and who called thoose > functions. > > Unfortunately this is not enough because the logic is missing how a > computer will be assigned to an image/reservation. As I saw this allocating > happens in Request.php (fn newReservation()) and maybe the main logic is in > Utils.php (fn allocComputer). You need to look at the isAvailable function in utils.php. That's where a computer is selected for any given reservation. > My problem is that there is no log that I can > use to backtrace what and when happening and I don't understand how this > allocating works. Correct - there is no log of how the computers are allocated. You can use the php function "error_log" to add your own logging to the isAvailable function to see what is happening. > Some questions: Is it random which available computer > will be used? If a computer is preloaded with the same image that a user > chose too then where and how will be taken this into account and filter > that computers which are preloaded with that image? By default, it is not random. Available computers are ordered first by whether or not they are currently loaded with the requested image, then by the specs of the computer with computers having the highest specs ranked first (however, that will be reversed in the next major release so that computers with the lowest specs will be ranked first). There is a config option in the conf.php file that will change the behavior so that computers are randomly assigned rather than being ranked by specs (they are still separated by preloaded/not preloaded). > What happens if a user > requests such an image that is not preloaded on any computer, is it problem > or only the provisioning time period will last a bit more? If a computer is not preloaded, it just makes the provisioning time longer. > Can someone explain the logic behind the allocating procedure and tell me > how the "computer-id" value of reservations table is calculated? See above. > Can you recommend me some technique to trace the "happenings" in php > scripts? I tried to use Zend Server instead of php5 server but there is > something wrong. Have you tried to use it with Zend Server, any > documentation or it shouldn't be problem? I've never used Zend Server. I'd recommend using the error_log function as described above. > Thank you in advance! You're welcome. > Best regards, > Norbert Josh > My advisor is Imre Kocsis and he suggested to mail here: > "Hi all, > > I am Norbert's advisor. Norbert, I think you should have posted this to the > 'dev' list rather than 'user'. Anyways, back in the summer when we started > getting our feet wet with VCL I managed to find only a short and incomplete > thread on the mailing list explaining the (largely undocumented) machine > allocation and preparation scheduling logic - so any help is greatly > appreciated. (Although based on our experience with the code base so far I > think the necessary information can be traced back from the source with > manageable effort.) > > To offer a bit of context to Norbert's questions: the larger goal is to > have a simple discrete event simulator for a hybrid VCL setup in order to > be able to play around with various reservation arrival processes, cost and > possibly fault models. (I know that 'hybrid' VCL setups - as in mixing an > in-house data center e.g. with EC2 - is not a technical reality for VCL > yet, but we are very interested in how it could work from the long-term > cost optimization and risk mitigation point of view for 'hardware budget > conscious' VCL setups.) > > After understanding the necessary parts of VCL, hopefully we will be able > to contribute some sort of documentation on (our understanding of) the > internals back to the community. > > Best regards > Imre" -- ------------------------------- Josh Thompson Systems Programmer Advanced Computing | VCL Developer North Carolina State University [email protected] 919-515-5323 my GPG/PGP key can be found at pgp.mit.edu All electronic mail messages in connection with State business which are sent to or received by this account are subject to the NC Public Records Law and may be disclosed to third parties.
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