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• SQL server virtual memory usage and perofrmance

  - by user365035

  Hello, I have a very large DB used mostly for analytics. The performance overall is very sluggish. I just noticed that when running the query below, the amount of virtual memory used greatly exceed the amount of physical memory available. Currently, phsycial memory is 10GB (10238 bytes) where as the virtual memory returns significantly more 8388607 bytes. That seems really wrong, but I'm at a bit of a loss on how to proceed. USE [master]; GO select cpu_count , hyperthread_ratio , physical_memory_in_bytes / 1048576 as 'mem_MB' , virtual_memory_in_bytes / 1048576 as 'virtual_mem_MB' , max_workers_count , os_error_mode , os_priority_class from sys.dm_os_sys_info

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• For what purpose does java have a float primitive type?

  - by Roman

  I heard plenty times different claims about float type in java. The most popular issues typicaly regard to converting float value to double and vice versa. I read (rather long time ago and not sure that it's actual now with new JVM) that float gives much worse performance then double. And it's also not recommended to use float in scientific applications which should have certain accuracy. I also remember that when I worked with AWT and Swing I had some problems with using float or double (like using Point2D.Float or Point2D.Double). So, I see only 2 advantages of float over double: it needs only 4 bytes while double needs 8 bytes JMM garantees that assignment operation is atomic with float variables while it's not atomic with double's. Are there any other cases where float is better then double? Do you use float's in your applications? It seems to me that the only valuable reason java has float is backward compatibility.

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• Does malloc() allocate a contiguous block of memory?

  - by user66854

  I have a piece of code written by a very old school programmer :-) . it goes something like this typedef struct ts_request { ts_request_buffer_header_def header; char package[1]; } ts_request_def; ts_request_buffer_def* request_buffer = malloc(sizeof(ts_request_def) + (2 * 1024 * 1024)); the programmer basically is working on a buffer overflow concept. I know the code looks dodgy. so my questions are: Does malloc always allocate contiguous block of memory ?. because in this code if the blocks are not contiguous , the code will fail big time Doing free(request_buffer) , will it free all the bytes allocated by malloc i.e sizeof(ts_request_def) + (2 * 1024 * 1024), or only the bytes of the size of the structure sizeof(ts_request_def) Do you see any evident problems with this approach , i need to discuss this with my boss and would like to point out any loopholes with this approach

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• Embedded "Smart" character LCD driver. Is this a good idea?

  - by chris12892

  I have an embedded project that I am working on, and I am currently coding the character LCD driver. At the moment, the LCD driver only supports "dumb" writing. For example, let's say line 1 has some text on it, and I make a call to the function that writes to the line. The function will simply seek to the beginning of the line and write the text (plus enough whitespace to erase whatever was last written). This is well and good, but I get the feeling it is horribly inefficient sometimes, since some lines are simply: "Some-reading: some-Value" Rather than "brute force" replacing the entire line, I wanted to develop some code that would figure out the best way to update the information on the LCD. (just as background, it takes 2 bytes to seek to any char position. I can then begin writing the string) My idea was to first have a loop. This loop would compare the input to the last write, and in doing so, it would cover two things: A: Collect all the differences between the last write and the input. For every contiguous segment (be it same or different) add two bytes to the byte count. This is referenced in B to determine if we are wasting serial bandwidth. B: The loop would determine if this is really a smart thing to do. If we end up using more bytes to update the line than to "brute force" the line, then we should just return and let the brute force method take over. We should exit the smart write function as soon as this condition is met to avoid wasting time. The next part of the function would take all the differences, seek to the required char on the LCD, and write them. Thus, if we have a string like this already on the LCD: "Current Temp: 80F" and we want to update it to "Current Temp: 79F" The function will go through and see that it would take less bandwidth to simply seek to the "8" and write "79". The "7" will cover the "8" and the "9" will cover the "0". That way, we don't waste time writing out the entire string. Does this seem like a practical idea?

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• IEnumerable<T> ToArray usage, is it a copy or a pointer?

  - by Daniel

  I am parsing an arbitrary length byte array that is going to be passed around to a few different layers of parsing. Each parser creates a Header and a Packet payload just like any ordinary encapsulation. And my problem lies in how the encapsulation holds its packet byte array payload. Say i have a 100 byte array, and it has 3 levels of encapsulation. 3 packet objects will be created and i want to set the payload of these packets to the corresponding position in the byte array of the packet. For example lets say the payload size is 20 for all levels, then imagine it has a public byte[] Payload on each object. However the problem is that this byte[] Payload is a copy of the original 100 bytes. So i'm going to end up with 160 bytes in memory instead of 100. If it were in c++ i could just easily use a pointer however i'm writing this in c#. So i created the following class: public class PayloadSegment<T> : IEnumerable<T> { public readonly T[] Array; public readonly int Offset; public readonly int Count; public PayloadSegment(T[] array, int offset, int count) { this.Array = array; this.Offset = offset; this.Count = count; } public T this[int index] { get { if (index < 0 || index >= this.Count) throw new IndexOutOfRangeException(); else return Array[Offset + index]; } set { if (index < 0 || index >= this.Count) throw new IndexOutOfRangeException(); else Array[Offset + index] = value; } } public IEnumerator<T> GetEnumerator() { for (int i = Offset; i < Offset + Count; i++) yield return Array[i]; } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { IEnumerator<T> enumerator = this.GetEnumerator(); while (enumerator.MoveNext()) { yield return enumerator.Current; } } } This way i can simply reference a position inside the original byte array but use positional indexing. However if i do something like: PayloadSegment<byte> something = new PayloadSegment<byte>(someArray, 5, 10); byte[] somethingArray = something.ToArray(); Will the somethingArray be a copy of the bytes, or a reference to the original PayloadSegment which in turn is a reference to the original byte array? Sorry it was hard to word this lol _<

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• What's the difference between unsigned long/long/int in c/c++?

  - by user198729

  It seems all of them take 4 bytes of space, so what's the difference?

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• What is the magic behind perl read() function and buffer which is not a ref ?

  - by alex8657

  I do not get to understand how the Perl read($buf) function is able to modify the content of the $buf variable. $buf is not a reference, so the parameter is given by copy (from my c/c++ knowledge). So how come the $buf variable is modified in the caller ? Is it a tie variable or something ? The C documentation about setbuf is also quite elusive and unclear to me # Example 1 $buf=''; # It is a scalar, not a ref $bytes = $fh->read($buf); print $buf; # $buf was modified, what is the magic ? # Example 2 sub read_it { my $buf = shift; return $fh->read($buf); } my $buf; $bytes = read_it($buf); print $buf; # As expected, this scope $buf was not modified

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• C# implementation of PushbackInputStream

  - by Mark Heath

  I need a C# implementation of Java's PushbackInputStream. I have made my own very basic one, but I wondered if there was a well tested and decently performing version already available somewhere. As it happens I always push back the same bytes I read so really it just needs to be able to reposition backwards, buffering up to a number of bytes I specify. (like Java's BufferedInputStream with the mark and reset methods). Update: I should add that I can't simply reposition the stream as CanSeek may be false. (e.g. when the input steam is a NetworkStream)

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• Is webserver bandwith the entire HTTP Request/Responce?

  - by Lienau

  Just a quick question. I'm making a web application where C++ communicates with a php script over HTTP Requests/Response. The data being set back and forth is quite small ~36 bytes. But I plan to have many computers connected, contacting the server quite often. I did the math, and I could potentially have gigabytes of data transfer a month. This isn't too much of problem, but it would be if the bandwidth included the request/response headers the request size would be about ~560 bytes. That's about 16x more bandwidth than I was planning... That would be a lot. If if any one knew how host determine bandwidth and could share, that'd be great. Thanks.

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• Discovering maximum packet size

  - by ereOn

  I'm working on a network-related project and I am using DTLS (TLS/UDP) to secure communications. Reading the specifications for DTLS, I've noted that DTLS requires the DF flag (Don't Fragment) to be set. On my local network if I try to send a message bigger than 1500 bytes, nothing is sent. That makes perfect sense. On Windows the sendto() reports a success but nothing is sent. I obviously cannot unset the DF flag manually since it is mandatory for DTLS and i'm not sure whether the 1500 bytes limit (MTU ?) could change in some situations. I guess it can. So, my question is : "Is there a way to discover this limit ?" If not, what would be the lowest possible value ? My software runs under UNIX (Linux/MAC OSX) and Windows OSes so different solutions for each OS are welcome ;) Many thanks.

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• grdb not working variables

  - by stupid_idiot

  hi, i know this is kinda retarded but I just can't figure it out. I'm debugging this: xor eax,eax mov ah,[var1] mov al,[var2] call addition stop: jmp stop var1: db 5 var2: db 6 addition: add ah,al ret the numbers that I find on addresses var1 and var2 are 0x0E and 0x07. I know it's not segmented, but that ain't reason for it to do such escapades, because the addition call works just fine. Could you please explain to me where is my mistake? I see the problem, dunno how to fix it yet though. The thing is, for some reason the instruction pointer starts at 0x100 and all the segment registers at 0x1628. To address the instruction the used combination is i guess [cs:ip] (one of the segment registers and the instruction pointer for sure). The offset to var1 is 0x10 (probably because from the begining of the code it's the 0x10th byte in order), i tried to examine the memory and what i got was: 1628:100 8 bytes 1628:108 8 bytes 1628:110 <- wtf? (assume another 8 bytes) 1628:118 ... whatever tricks are there in the memory [cs:var1] points somewhere else than in my code, which is probably where the label .data would usually address ds.... probably.. i don't know what is supposed to be at 1628:10 ok, i found out what caused the assness and wasted me whole fuckin day. the behaviour described above is just correct, the code is fully functional. what i didn't know is that grdb debugger for some reason sets the begining address to 0x100... the sollution is to insert the directive ORG 0x100 on the first line and that's the whole thing. the code was working because instruction pointer has the right address to first instruction and goes one by one, but your assembler doesn't know what effective address will be your program stored at so it pretty much remains relative to first line of the code which means all the variables (if not using label for data section) will remain pointing as if it started at 0x0. which of course wouldn't work with DOS. and grdb apparently emulates some DOS features... sry for the language, thx everyone for effort, hope this will spare someone's time if having the same problem... heheh.. at least now i know the reason why to use .data section :))))

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• how to set 'utf-8' enable on my site..using django

  - by zjm1126

  my error: UnicodeDecodeError at /mytest/write/ 'utf8' codec can't decode bytes in position 137-138: invalid data

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• Analyzing Python Code: Modulus Operator

  - by Bhubhu Hbuhdbus

  I was looking at some code in Python (I know nothing about Python) and I came across this portion: def do_req(body): global host, req data = "" s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((host, 80)) s.sendall(req % (len(body), body)) tmpdata = s.recv(8192) while len(tmpdata) > 0: data += tmpdata tmpdata = s.recv(8192) s.close() return data This is then called later on with body of huge size, as in over 500,000 bytes. This is sent to an Apache server that has the max request size on the default 8190 bytes. My question is what is happening at the "s.sendall()" part? Obviously the entire body cannot be sent at once and I'm guessing it is reduced by way of the modulus operator. I don't know how it works in Python, though. Can anyone explain? Thanks.

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• Ruby TCPSocket doesn't notice it when server is killed

  - by user303308

  I've this ruby code that connects to a TCP server (namely, netcat). It loops 20 times, and sends "ABCD ". If I kill netcat, it takes TWO iterations of the loop for an exception to be triggered. On the first loop after netcat is killed, no exception is triggered, and "send" reports that 5 bytes have been correctly written... Which in the end is not true, since of course the server never received them. Is there a way to work around this issue ? Right now I'm losing data : since I think it's been correctly transfered, I'm not replaying it. #!/usr/bin/env ruby require 'rubygems' require 'socket' sock = TCPSocket.new('192.168.0.10', 5443) sock.sync = true 20.times do sleep 2 begin count = sock.write("ABCD ") puts "Wrote #{count} bytes" rescue Exception => myException puts "Exception rescued : #{myException}" end end

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• Delays in .net app when connecting to oracle db using Oracle.DataAccess

  - by chris

  I have a .net desktop app that connects to an oracle database. At times, there are very noticable delays. I ran a trace on the code, and it was always in the DataReader.Read(). I turned on sql tracing, and found the following, which corresponds to the delays I'm seeing: (2128) [23-MAR-2010 13:00:07:310] nsprecv: reading from transport... (2128) [23-MAR-2010 13:00:07:310] nttrd: entry (2128) [23-MAR-2010 13:00:24:655] nttrd: socket 676 had bytes read=2047 (2128) [23-MAR-2010 13:00:24:655] nttrd: exit (2128) [23-MAR-2010 13:00:24:655] nsprecv: 2047 bytes from transport There's about a 14 second pause in there. I'm pretty sure that there's not a problem in the code, but not sure where to look at next. Is there anyone out there with experience with oracle trace that can explain what's going on?

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• android java.lang.OutOfMemoryError

  - by xiangdream

  hi, all, when i download large data from website, i got this error information: I/global (20094): Default buffer size used in BufferedInputStream constructor. It would be better to be explicit if an 8k buffer is required. D/dalvikvm(20094): GC freed 6153 objects / 3650840 bytes in 335ms I/dalvikvm-heap(20094): Forcing collection of SoftReferences for 3599051-byte al location D/dalvikvm(20094): GC freed 320 objects / 11400 bytes in 144ms E/dalvikvm-heap(20094): Out of memory on a 3599051-byte allocation. I/dalvikvm(20094): "Thread-9" prio=5 tid=17 RUNNABLE I/dalvikvm(20094): | group="main" sCount=0 dsCount=0 s=0 obj=0x439b9480 I/dalvikvm(20094): | sysTid=25762 nice=0 sched=0/0 handle=4065496 anyone can help me?

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• Haskell optimization of the following function

  - by me2

  Profiling of some code of mine showed that about 65% of the time I was running the following code. What it does is use the Data.Binary.Get monad to walk through a bytestring looking for the terminator. If it detects 0xff, it checks if the next byte is 0x00. If it is, it drops the 0x00 and continues. If it is not 0x00, then it drops both bytes and the resulting list of bytes is converted to a bytestring and returned. Any obvious ways to optimize this code? I can't see it. parseECS = f [] False where f acc ff = do b <- getWord8 if ff then if b == 0x00 then f (0xff:acc) False else return $ L.pack (reverse acc) else if b == 0xff then f acc True else f (b:acc) False

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• View returned file from Webservice method

  - by gafda

  I already have a method in my webservice that returns a byte[] containing only the bytes of the file downloading. The invocation is something like: http://www.mysite.com/myWebservice.asmx with: string fileId = "123"; bytes[] fileContent = myWebservice.Download(fileId); What I wanted to do is be able to invoke this method or other (to be made) on a aspx webpage and be able to open a browser window containing the real content of the file. i.e. Most files are TXT and PDF. (Assuming the client has the PDF plugin that alows him\her to view PDF's on the browser.)

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• Hyper-V monitor virtual machine disk activity

  - by iulianchira

  How can I get the number of bytes read from/written into the physical disk of the host system by Hyper-V virtual machines?

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• Python - network buffer handling question...

  - by Patrick Moriarty

  Hi, I want to design a game server in python. The game will mostly just be passing small packets filled with ints, strings, and bytes stuffed into one message. As I'm using a different language to write the game, a normal packet would be sent like so: Writebyte(buffer, 5); // Delimit type of message Writestring(buffer, "Hello"); Sendmessage(buffer, socket); As you can see, it writes the bytes to the buffer, and sends the buffer. Is there any way to read something like this in python? I am aware of the struct module, and I've used it to pack things, but I've never used it to actually read something with mixed types stuck into one message. Thanks for the help.

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• MySQL: Efficient Blobbing?

  - by feklee

  I'm dealing with blobs of up to - I estimate - about 100 kilo bytes in size. The data is compressed already. Storage engine: InnoDB on MySQL 5.1 Frontend: PHP (Symfony with Propel ORM) Some questions: I've read somewhere that it's not good to update blobs, because it leads to reallocation, fragmentation, and thus bad performance. Is that true? Any reference on this? Initially the blobs get constructed by appending data chunks. Each chunk is up to 16 kilo bytes in size. Is it more efficient to use a separate chunk table instead, for example with fields as below? parent_id, position, chunk Then, to get the entire blob, one would do something like: SELECT GROUP_CONCAT(chunk ORDER BY position) FROM chunks WHERE parent_id = 187 The result would be used in a PHP script. Is there any difference between the types of blobs, aside from the size needed for meta data, which should be negligible.

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• While saving a PNG image using NSData writetofile saves corrupted data on the iphone disk

  - by jAmi

  I have a number of images (PNG,GIF and JPG) in my Application Resource Bundle. I want some images to be saved in my Documents Directory so i use : imgPath=[documentsDirectoryPath stringByAppendingPathComponent:@"myImage.png"]; if (![fileMgr fileExistsAtPath:imgPath]) { [[fileMgr contentsAtPath:[[NSBundle mainBundle] pathForResource:@"myImage"ofType:@"png"]] writeToFile:imgPath atomically:NO]; } This saves an Image file on my desired Path but this file has an Extra 300 bytes (of maybe junk data) in it which results in a corrupted image... Am i doing something wrong here? This works in the simulator but on the real device the image has some extra 300 bytes. Also a GIF image gets copied nicely and works but this problem occurs for PNG image.

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• Efficiently display file status when using background thread

  - by schmoopy

  How can i efficiently display the status of a file when using a background thread? For instance, lets say i have a 100MB file: when i do the code below via a thread (just as an example) it runs in about 1 min: foreach(byte b in file.bytes) { WriteByte(b, xxx); } But... if i want to update the user i have to use a delegate to update the UI from the main thread, the code below takes - FOREVER - literally i don't know how long im still waiting, ive created this post and its not even 30% done. int total = file.length; int current = 0; foreach(byte b in file.bytes) { current++; UpdateCurrentFileStatus(current, total); WriteByte(b, xxx); } public delegate void UpdateCurrentFileStatus(int cur, int total); public void UpdateCurrentFileStatus(int cur, int total) { // Check if invoke required, if so create instance of delegate // the update the UI if(this.InvokeRequired) { } else { UpdateUI(...) } }

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• Change HttpContext.Request.InputStream

  - by user320478

  I am getting lot of errors for HttpRequestValidationException in my event log. Is it possible to HTMLEncode all the inputs from override of ProcessRequest on web page. I have tried this but it gives context.Request.InputStream.CanWrite == false always. Is there any way to HTMLEncode all the feilds when request is made? public override void ProcessRequest(HttpContext context) { if (context.Request.InputStream.CanRead) { IEnumerator en = HttpContext.Current.Request.Form.GetEnumerator(); while (en.MoveNext()) { //Response.Write(Server.HtmlEncode(en.Current + " = " + //HttpContext.Current.Request.Form[(string)en.Current])); } long nLen = context.Request.InputStream.Length; if (nLen > 0) { string strInputStream = string.Empty; context.Request.InputStream.Position = 0; byte[] bytes = new byte[nLen]; context.Request.InputStream.Read(bytes, 0, Convert.ToInt32(nLen)); strInputStream = Encoding.Default.GetString(bytes); if (!string.IsNullOrEmpty(strInputStream)) { List<string> stream = strInputStream.Split('&').ToList<string>(); Dictionary<int, string> data = new Dictionary<int, string>(); if (stream != null && stream.Count > 0) { int index = 0; foreach (string str in stream) { if (str.Length > 3 && str.Substring(0, 3) == "txt") { string textBoxData = str; string temp = Server.HtmlEncode(str); //stream[index] = temp; data.Add(index, temp); index++; } } if (data.Count > 0) { List<string> streamNew = stream; foreach (KeyValuePair<int, string> kvp in data) { streamNew[kvp.Key] = kvp.Value; } string newStream = string.Join("", streamNew.ToArray()); byte[] bytesNew = Encoding.Default.GetBytes(newStream); if (context.Request.InputStream.CanWrite) { context.Request.InputStream.Flush(); context.Request.InputStream.Position = 0; context.Request.InputStream.Write(bytesNew, 0, bytesNew.Length); //Request.InputStream.Close(); //Request.InputStream.Dispose(); } } } } } } base.ProcessRequest(context); }

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• C socket programming: recv / select not seeing sent messages

  - by Fantastic Fourier

  Hey guys, I had some questions, about socket programming for client-server using TCP/IP. I am using select() to recv(), which works fine when client send() messages to server, but not the other way around. The send() returns positive (and reasonable) numbers of bytes sent by server but I know that the nubmer of bytes "sent" really means "sent out of the socket", not "sent and was received by the client." The select() function seems to work fine. So given that, my guess is that it's the send() function that is giving me the problem. Probably the address of client in send() is not correct. But when I compared address.sin_addr.s_addrmember (it's an unsigned long int) of struct sockaddr_in from recv() and send() of server, they are identical. So I am kind of lost as to what could be wrong?

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