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Transaction isolation levels relation with locks on table
...y use: MVCC or Two Phase Locking.
CUBRID (open source RDBMS) explains the idea of this two algorithms:
Two-phase locking (2PL)
The first one is when the T2 transaction tries to change the A record,
it knows that the T1 transaction has already changed the A record and
waits until ...
Best explanation for languages without null
...ave to ask yourself "can this be null? Do I need to check for null here?"
Ideally, in the many cases where null doesn't make sense, it shouldn't be allowed.
That's tricky to achieve in .NET, where nearly everything can be null. You have to rely on the author of the code you're calling to be 100% d...
How to explain callbacks in plain english? How are they different from calling one function from ano
...y to user interaction events (like mouse clicks). In this case, the whole idea is to wait for a contingent event to occur before executing the custom functionality. This is obvious in the case of user interaction, but is also important in i/o (input/output) processes that can take time, like readin...
How do CDI and EJB compare? interact?
...llows you to inject implementation into your service or whatever. The main idea is that class, where you inject, should be managed by EJB container.
Seems that CDI does understand what EJB is, so in Java EE 6 compliant server, in your servlet you can write both
@EJB EJBService ejbService;
and
@Inje...
How do I create a simple 'Hello World' module in Magento?
... experienced programmer or don't have access to an experienced programmer (ideally in PHP and Java), pick another cart. Magento is well engineered, but it was engineered to be a shopping cart solution that other programmers can build modules on top of. It was not engineered to be easily understood b...
Cookie blocked/not saved in IFRAME in Internet Explorer
...wants you to define a P3P header if you are using cookies.
This is a nice idea, and luckily most of the time not providing this header won't cause any issues (read browser warnings). Unless your website/web application is loaded into an other website using an (i)Frame. This is where IE becomes a ma...
Referring to the null object in Python
... pass
You need to understand the implications and why it's often a good idea to be explicit.
Case 1: testing if a value is None
Why do
value is None
rather than
value==None
?
The first is equivalent to:
id(value)==id(None)
Whereas the expression value==None is in fact applied like this
value._...
How do JavaScript closures work?
...er may now seem incredibly silly & out of place. Hopefully the general idea of the story remains fun for some.
I'm a big fan of analogy and metaphor when explaining difficult concepts, so let me try my hand with a story.
Once upon a time:
There was a princess...
function princess() {
She...
Flags to enable thorough and verbose g++ warnings
...ver,
turning on this warning can enforce something that is probably a good
idea. For cases where you explicitly want to ignore everything except
the listed possibilities (but other numbers are possible), then put
in default: break; to make it explicit. If you explicitly enumerate
all possibilities, ...
How does Google Instant work?
Any ideas on exactly how the new google instant search works? It seems to just be AJAX calls to the old search, but it's pretty hard to simplify Google that much. Anybody have speculations?
...