I'm building a student schedule generator and I need a way of producing more than one solution. Is there some way to save off feasible scores or scores of Xhard/Ysoft?
I need to be able to output more than one potential schedule, that way the student will have a choice for one schedule over the other if for whatever reason they don't want the "best" schedule (maybe they don't like one of the professors, maybe they don't want an 8am class, whatever)
My original idea was to save off all feasible solutions using the bestSolutionChanged event listener. The problem with this, is that once it finds a 0hard/0soft score, it ignores all scores after that, including scores that are equal.
Ideally I'd like to save off all scores of 0hard/-3soft or better, but just being able to save any feasible scores or force optaplanner to look for a new best score would be useful as well.
This is not a solution, but an analysis of the problem:
Hacking the BestSolutionRecaller is obviously not just a big pain, it's also behaviour we don't want to encourage as it makes upgrading to newer version an even bigger pain. So don't expect us to solve this by adding an easy way to configure that in the solver config any time soon. That being said, a solution for this common problem is clearly needed.
When a new best solution is found, it is planning cloned (see docs for definition) from the working solution (the internal solution in OptaPlanner). This allow us to remember that new best solution as the working solution solution changes. That also means the BestSolutionChangedEvents gets a plannng clone and can safely ship it to another thread, for example to marshal it to a client (presuming any ProblemFactChanges you create do copies instead of alterations), without being corrupted by the solver thread that modifies the working solution.
New best solution imply that workingScore > bestScore. The moment it instead does workingScore >= bestScore, we need far more planning clones (which are a bit CPU expensive), but we could then just send out BestSolutionChangedEvents for that too, if and only if a flag is enabled of course, because most users (unlike yourself) don't want this behaviour.
One proposal is to create a separate BestSolutionChangedOrSameEvent, next to the BestSolutionChangedEvent. This might not be ideal, because we need to be able to detect whether or not someone needs those extra planning clones.
Another proposal is to just have a flag in the <solver> config that switches from > to >= behavior for BestSolutionChangedEvent.
Please create a jira (see "get help" on webpage) and link it it here, or create a support ticket (also see "get help" on webpage).
Related
I'm using Optaplanner to automatically solve school timetables. After a timetable has been solved the user will manually change some lessons and will get feedback on how this affects the score via the following call:
scoreManager.updateScore(timetable);
This call takes some 200ms and will, I assume, do a complete evaluation. Im trying to optimize this and want to only pass in a Move object so that Optaplanner only has to recalculate the delta, like:
scoreManager.updateScore(previousTimetable,changeMove);
Is there a way to do this?
There really is no way how to do just a single move. You don't do moves - the solver does moves. You can only make external problem changes to the solution. You should look into the ProblemChange interface and its use in the SolverManager.
However, the problem change will likely reset the entire working solution anyway. And after the external change is done, you're not guaranteed that the solution will still make sense. (What if it breaks hard constraints now?) You simply need to expect and account for the fact that, after users submit their changes, the solver will need to run; possibly even for a prolonged period of time.
My solution is for VRPTW and I've created a Custom Move.
After a custom move has been tried (prior to being accepted), I would like to see a score breakdown of it (not just the score itself).
Where is a good location to use ScoreExplanation to see the detailed score breakdown? Eg. in my AbstractMove implementation somewhere?
I have TRACE mode on and can see the score. I've tried pulling it up upon the next custom move being run and it seemed to be working since it was retrieving the correct score from the previous custom move, but when I looked at the ScoreExplanation, it looks completely off (it doesn't add up to the score).
Score explanations are not designed to be used inside of a step, they are far too slow for that. You are free to use the ScoreManager API any time you like, but you will pay a heavy performance penalty if you do that on the solver thread or the move threads.
In the change and swap move selector, I would like to only consider moves that involve entities in conflict as they are more likely to improve the heuristic score.
How should this be done? What classes and interfaces do I have to reuse/extend? I looked at ScoreDirector and PhaseLifecycleListener.
A MoveFilter might do that (if it's not in phase or solver cached as it changes ever step). See the course scheduling example and docs for how to use a filter.
I wouldn't recommend it though, as you still want to move non-conflicting entities at times. You might just want to focus more on those conflicting lectures. So I would keep a vanilla move selector in the mix.
The move filter isn't perfect either - the Guided Local Search feature (not yet available) is a better way to deal with this.
However, given the other question about the model and similar cases I 've seen, I 'd say moves are not your problem. A better model will make all these kinds of move tweaking obsolete.
Lately I need to do an impact analysis on changing a DB column definition of a widely used table (like PRODUCT, USER, etc). I find it is a very time consuming, boring and difficult task. I would like to ask if there is any known methodology to do so?
The question also apply to changes on application, file system, search engine, etc. At first, I thought this kind of functional relationship should be pre-documented or some how keep tracked, but then I realize that everything can have changes, it would be impossible to do so.
I don't even know what should be tagged to this question, please help.
Sorry for my poor English.
Sure. One can technically at least know what code touches the DB column (reads or writes it), by determining program slices.
Methodology: Find all SQL code elements in your sources. Determine which ones touch the column in question. (Careful: SELECT ALL may touch your column, so you need to know the schema). Determine which variables read or write that column. Follow those variables wherever they go, and determine the code and variables they affect; follow all those variables too. (This amounts to computing a forward slice). Likewise, find the sources of the variables used to fill the column; follow them back to their code and sources, and follow those variables too. (This amounts to computing a backward slice).
All the elements of the slice are potentially affecting/affected by a change. There may be conditions in the slice-selected code that are clearly outside the conditions expected by your new use case, and you can eliminate that code from consideration. Everything else in the slices you may have inspect/modify to make your change.
Now, your change may affect some other code (e.g., a new place to use the DB column, or combine the value from the DB column with some other value). You'll want to inspect up and downstream slices on the code you change too.
You can apply this process for any change you might make to the code base, not just DB columns.
Manually this is not easy to do in a big code base, and it certainly isn't quick. There is some automation to do for C and C++ code, but not much for other languages.
You can get a bad approximation by running test cases that involve you desired variable or action, and inspecting the test coverage. (Your approximation gets better if you run test cases you are sure does NOT cover your desired variable or action, and eliminating all the code it covers).
Eventually this task cannot be automated or reduced to an algorithm, otherwise there would be a tool to preview refactored changes. The better you wrote code in the beginning, the easier the task.
Let me explain how to reach the answer: isolation is the key. Mapping everything to object properties can help you automate your review.
I can give you an example. If you can manage to map your specific case to the below, it will save your life.
The OR/M change pattern
Like Hibernate or Entity Framework...
A change to a database column may be simply previewed by analysing what code uses a certain object's property. Since all DB columns are mapped to object properties, and assuming no code uses pure SQL, you are good to go for your estimations
This is a very simple pattern for change management.
In order to reduce a file system/network or data file issue to the above pattern you need other software patterns implemented. I mean, if you can reduce a complex scenario to a change in your objects' properties, you can leverage your IDE to detect the changes for you, including code that needs a slight modification to compile or needs to be rewritten at all.
If you want to manage a change in a remote service when you initially write your software, wrap that service in an interface. So you will only have to modify its implementation
If you want to manage a possible change in a data file format (e.g. length of field change in positional format, column reordering), write a service that maps that file to object (like using BeanIO parser)
If you want to manage a possible change in file system paths, design your application to use more runtime variables
If you want to manage a possible change in cryptography algorithms, wrap them in services (e.g. HashService, CryptoService, SignService)
If you do the above, your manual requirements review will be easier. Because the overall task is manual, but can be aided with automated tools. You can try to change the name of a class's property and see its side effects in the compiler
Worst case
Obviously if you need to change the name, type and length of a specific column in a database in a software with plain SQL hardcoded and shattered in multiple places around the code, and worse many tables present similar column namings, plus without project documentation (did I write worst case, right?) of a total of 10000+ classes, you have no other way than manually exploring your project, using find tools but not relying on them.
And if you don't have a test plan, which is the document from which you can hope to originate a software test suite, it will be time to make one.
Just adding my 2 cents. I'm assuming you're working in a production environment so there's got to be some form of unit tests, integration tests and system tests already written.
If yes, then a good way to validate your changes is to run all these tests again and create any new tests which might be necessary.
And to state the obvious, do not integrate your code changes into the main production code base without running these tests.
Yet again changes which worked fine in a test environment may not work in a production environment.
Have some form of source code configuration management system like Subversion, GitHub, CVS etc.
This enables you to roll back your changes
An interesting problem occured recently, and I've been thinking of the "best" way (for a given value of "best") to implement this.
In essence, it's one of tracking notes against source code. The example that flagged this was getting a problem fixed in live within SLAs, and how to best achieve this. Without going into all the details, it came down to finding a function that's used in a number of places which may or may not be buggy, yet the problem was being reporting only in a single location.
The fix to meet the SLAs was simply to add a check into the location where the problem was reported, rather than tweaking the common code and having to test everything that touches that function.
The interesting issue is then for upstreaming. The "correct" method would then be to go back and check the original function, validate it's correct for everywhere it's called and then make the change "properly" if its determined the library function is wrong.
The problem is this takes time, so upstreaming may simply take the workaround, etc. However if the problem occurs again (say six months later) in another location calling the same library function, there isn't an easy way to link the two problems together. You can search the bug tracking database, but this isn't guranteed to help - it depends if a note's been added saying something along the lines of "this library function needs more thorough checking, but no time to investigate now".
So the question is this: within a large team of developers (30 plus, split into teams of both support and on-going development), what methods do you use to manage (what are effectively) "sticky notes" against source code, short of adding a comment to the suspicious function's source code saying "this might be a bit dodgy"?
The problem with the commiting a comment is one of process: a change is a change, so committing a zero-change change (i.e., one where just comments are added) is not ideal; developers can make mistakes even adding a comment (hit a stray key or something) so it's always (IMO) better to commit only where actual changes are made.
Now a wiki could be used to track per-file notes, but we've got a minimum of four branches and inexcess of a few hundred files (SQL objects, source code, XML files, etc), so a wiki will get unmangable quite quickly.
This is the sort of thing that it would be nice if SCM's could support - bits of metadata against files that are simply notes, but don't add to the SCM's version history - that can be displayed when doing (say) an svn update, or manually viewed.
There may already be solutions out there -- so how do you manage this type of knowledge sharing?
Well we're now using this method: in each folder checked into SVN, we've created a .url shortcut (this is Windows we're dev'ing on) that links to a page on our development wiki about that folder. Thus we can update the Wiki info freely, and on checkout/update everyone gets a link that will take them to the appropriate Wiki page for that folder/module.
We've not long instigated it so we'll have to see how well it works long term -- but it's better than what we had before (i.e., nothing :-) ).