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com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
...sing or wrong in JDBC URL.
DB server is down.
DB server doesn't accept TCP/IP connections.
DB server has run out of connections.
Something in between Java and DB is blocking connections, e.g. a firewall or proxy.
To solve the one or the other, follow the following advices:
...
What is the difference between AF_INET and PF_INET in socket programming?
...s Format, Internet = IP Addresses
PF_INET = Packet Format, Internet = IP, TCP/IP or UDP/IP
AF_INET is the address family that is used for the socket you're creating (in this case an Internet Protocol address). The Linux kernel, for example, supports 29 other address families such as UNIX sockets a...
What is the use of ByteBuffer in Java? [closed]
...enever you need to do fast low-level I/O. If you were going to implement a TCP/IP protocol or if you were writing a database (DBMS) this class would come in handy.
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Are GUID collisions possible?
...r than the chance of not detecting a corrupt TCP/IP packet (~1 in 10^10). http://wwwse.inf.tu-dresden.de/data/courses/SE1/SE1-2004-lec12.pdf, page 11. This is also true of disk drives, cd drives, etc...
GUIDs are statistically unique and the data you read from the db is only statistically correct...
Right query to get the current number of connections in a PostgreSQL DB
...eUploader: {
brandingHtml: "Powered by \u003ca href=\"https://imgur.com/\"\u003e\u003csvg class=\"svg-icon\" width=\"50\" height=\"18\" viewBox=\"0 0 50 18\" fill=\"none\" xmlns=\"http://www.w3.org/2000/svg\"\u003e\u003cpath d=\"M46.1709 9.17788C46.1709 8.26454 46.2665 7.94324 4...
Difference between declaring variables before or in loop?
...gt;: mov rbp,rsp
0x00000000004004ba <+4>: mov DWORD PTR [rbp-0x4],0x0
0x00000000004004c1 <+11>: jmp 0x4004cd <main+23>
0x00000000004004c3 <+13>: mov eax,DWORD PT
What is stack unwinding?
...- see RAII referred to by Nikolai, and the documentation for boost::scoped_ptr or this example of using boost::mutex::scoped_lock.
program consistency: the C++ specifications state that you should never throw an exception before any existing exception has been handled. This means that the stack unwi...
windows service vs scheduled task
...th lots of experts telling you how it is really bad programming practice:
http://msmvps.com/blogs/peterritchie/archive/2007/04/26/thread-sleep-is-a-sign-of-a-poorly-designed-program.aspx
So you'll scratch your head and think to yourself, WTF, Undo Pending Checkouts -> Yes, I'm sure -> Undo a...
Bitwise operation and usage
...pecific meaning, in terms of instructions, for that port (see for instance http://en.wikipedia.org/wiki/Parallel_port). If you want to build software that does something with that hardware you will need bitwise operations to translate the instructions you want to execute to the bytes that the port u...
How does free know how much to free?
...n array? Why wouldn't they make it possible to do something like blockSize(ptr) if they're storing the information anyway?
– corsiKa
Jun 14 '14 at 1:12
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