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When and why are database joins expensive?
...ires retrieval of only the keys. In practice, not even the key values are fetched: the key hash values are used for join comparisons, mitigating the cost of multi-column joins and radically reducing the cost of joins involving string comparisons. Not only will vastly more fit in cache, there's a lot...
What is the difference between concurrent programming and parallel programming?
...O bound but not always, e.g. concurrent garbage collectors are entirely on-CPU. The pedagogical example of a concurrent program is a web crawler. This program initiates requests for web pages and accepts the responses concurrently as the results of the downloads become available, accumulating a set ...
Why does JPA have a @Transient annotation?
...ystem uses tools to generate entities from database. (Hibernate has those, etc...)
Now, suppose that by your business logic you need a particular field NOT to be persisted. You have to "configure" your entity in a particular way.
While Transient keyword works on an object - as it behaves within a j...
Increasing the maximum number of TCP/IP connections in Linux
... eth0 txqueuelen 5000
echo "/sbin/ifconfig eth0 txqueuelen 5000" >> /etc/rc.local
Similarly bump up the values for net.core.netdev_max_backlog and net.ipv4.tcp_max_syn_backlog. Their default values are 1000 and 1024 respectively.
sysctl net.core.netdev_max_backlog=2000
sysctl net.ipv4.tcp_m...
Debug vs. Release performance
...oven to be invariants
code written under #debug directive is not included, etc.
The rest is up to the JIT.
Full list of optimizations here courtesy of Eric Lippert.
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C# DateTime.Now precision
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Why would DateTime.Now be made less precise than what most CPU clocks could handle?
A good clock should be both precise and accurate; those are different. As the old joke goes, a stopped clock is exactly accurate twice a day, a clock a minute slow is never accurate at any time. Bu...
How to check if a file is a valid image file?
...more about it than just the format, like bitmap dimensions, format version etc.. So you might see this as a superficial test for "validity".
For other definitions of "valid" you might have to write your own tests.
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What integer hash function are good that accepts an integer hash key?
...tegers that are divisible by a common factor (word-aligned memory adresses etc.). Now if your hash table happens to be divisible by the same factor, you end up with only half (or 1/4, 1/8, etc.) buckets used.
– Rafał Dowgird
Mar 20 '09 at 16:56
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Do on-demand Mac OS X cloud services exist, comparable to Amazon's EC2 on-demand instances? [closed]
... just a data storage service, rather than a service allowing remote login, etc.)
5 Answers
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Which is faster in Python: x**.5 or math.sqrt(x)?
... Took 0.157436 seconds Took 0.093905 seconds Target system: Ubuntu Linux CPU: Intel(R) Core(TM)2 Duo CPU T9600 @ 2.80GHz As you can see I got different results. According to this your answer is not generic.
– zoli2k
Apr 23 '10 at 3:37
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