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I'm planning to use Node for my next project, because it seems to be a good fit for the problem I'm solving.
One thing I need to figure out is optimistic and pessimistic locking. http://guides.rubyonrails.org/active_record_querying.html#locking-records-for-update
Say, the user has a balance of 1. Two Node instances make requests concurrently to withdraw 1. The two requests could pass the check of sufficient balance at the same time, thus making two successful withdrawals resulting in a balance of -1.
Rails provides a wrapper around Postgres transactional and locking features. Does some kind of similar wrapper exist for Node?
How do you solve this in Node/Postgresql?
I know this is a database feature, but I wonder if Node or some library provides a abstraction away from writing raw SQL queries?
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I'm looking for a module - if it exists - that is an API for creating a traditional tree data structure (like a decision tree) and saving and loading it from a data source (like a MongoDB document). Ideally this API would allow splicing trees at any node and then resaving them to the DB and also retrieval of any node via an ID.
I've found the following:
decision-tree: too narrow a definition and no DB support.
simple-tree: no DB support
tree: no documentation
tree-kit: utilities but not a traditional tree data structure from what I can see.
tree-data: no documentation that I can find
None of these seem to be a full solution for my decision-tree needs. And it is quite possible that I'm approaching this the wrong way.
Suggestions?
EDIT:
Found tree-model and it seems promising, but still no API for interaction with a DB. Perhaps I will write one.
After looking into this and not finding a substantial solution for what I wanted, I wrote my own:
mongo-tree
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I was told once there is a book that shows you how to make a database from scratch using sed, awk, and the Linux filesystem. I thought I had the name, but now I cannot find it. What is this book called?
Edit:
My understanding is this book was meant for learning how databases work, and how to build your own entirely from scratch using awk and the filesystem. From how it was explained, you could build your own version of /rdb, then when you finished you could just use /rdb itself, but now you'd know how it was made.
So, at the end of the book, you'd have almost completely remade /rdb yourself.
Is it "Unix Relational Database Management: Application Development in the Unix Environment (/RDB)" http://www.amazon.com/exec/obidos/ISBN=013938622X/cbbrownecompu-20/ ?
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I would like to start writing lots of tiny "utility" NodeJS-based apps -- things like stream filters, generators, and the like, that might be 30-40LOC each. Each one would consume nearly zero CPU, RAM, or bandwidth (when the overhead of NodeJS and OS processes are factored out). The point is, I want a simple way to run thousands of them.
What do I need? Are there any PaaS's that can run thousands of NodeJS apps for a reasonable price ($10/mo)? Is there some kind of middleware that can give me thousands of sandboxed "partitions" on top of one Node process? Or is there some binary that's made for this that I could put on a VPS?
You can use vm module for sandboxing javascript code. It is still in works, be sure to read the caveats.
Functions that you can use:
runInThisContext: runs code in a separate context (but has access to global vars, not local).
runInNewContext: takes a seperate set of global var for context.
runInContext: takes a Context object(previously defined), for running the code.
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As I read through UML user guide chapter1, Principles of Modeling the First principle is
The choice of what models to create has a profound influence on how a
problem is attacked and how a solution is shaped In other words,
choose your models well. The right models will brilliantly illuminate
the most wicked development problems, offering insight that you simply
could not gain otherwise; the wrong models will mislead you, causing
you to focus on irrelevant issues.
1- I wonder if there is considerations I should take it into account while choosing UML models for a problem?
2- Where can I find this type of information?
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I'd like to improve my understanding of NTFS semantics; ideally, I'd like some kind of specification document(s).
I could (in theory) figure out the basics by experimentation, but there's always the possibility that I'd be ignoring some important variable.
For example, I'm having difficulty finding definitive information on the following:
(1) When do file times (created/modified/accessed) get set/updated? For example, does copying and/or moving a file affect any or all of these times? What about if the file is being copied/moved between volumes? What about alternate streams?
(2) How do sharing modes and read/write access interact?
(3) What happens to security information (SACL, DACL, ownership etc.) when a file is copied and/or moved?
As I said, I could probably "answer" these questions by writing some code, but that would only tell me how the specific operations I tested behaved across any machines that I ran the code on. I'd like to find a resource that can tell me how this stuff is supposed to behave, identifying all the variables that could affect the behaviour.
TIA!
Apparently there are no public non-NDA specifications. Projects such as NTFS-3G would greatly benefit from them, but they don't mention anything.
A predecessor of NTFS-3G, called linux-ntfs, has made some documentation on its own here. Maybe that's good enough for you, maybe not.