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Posts Tagged ‘php’

Caching SQL results with PHP

Monday, May 12th, 2008

I’ve been looking around lately on the best way to cache SQL results in PHP. I found some interesting articles posted in lots of places, but I didn’t find any that exactly matches my needs. The problem I have on hand is basically the same every growing website faces: decreasing mean resource usage per page request.

Now – this is my plan A to keep up with the website’s growth without a lot of hardware upgrades. There is a plan B, but I will keep that to a later post.

Creating a tar gz on the fly using PHP

Thursday, March 27th, 2008

A while ago, I thought about creating a tar.gz file for every download, so that if someone runs a search, he/she then can download all the images in the results. After a little bit of research, I found that PHP has a function for gzip. I also knew that the tar format just sticks files after one another, so if I can implement the tar format in PHP then I can gzip all images in the results.

I found this LGPL code that implemented the tar format. I used it (and modified it a little bit) to produce the online tar.gz functions:

  1. // Computes the unsigned Checksum of a file’s header
  2. // to try to ensure valid file
  4. function __computeUnsignedChecksum($bytestring)
  5. {
  6.   for($i=0; $i<512; $i++)
  7.     $unsigned_chksum += ord($bytestring[$i]);
  8.   for($i=0; $i<8; $i++)
  9.     $unsigned_chksum -= ord($bytestring[148 + $i]);
  10.   $unsigned_chksum += ord(" ") * 8;
  12.   return $unsigned_chksum;
  13. }
  15. // Generates a TAR file from the processed data
  17. function tarSection($Name, $Data, $information=NULL)
  18. {
  19.   // Generate the TAR header for this file
  21.   $header .= str_pad($Name,100,chr(0));
  22.   $header .= str_pad("777",7,"0",STR_PAD_LEFT) . chr(0);
  23.   $header .= str_pad(decoct($information["user_id"]),7,"0",STR_PAD_LEFT) . chr(0);
  24.   $header .= str_pad(decoct($information["group_id"]),7,"0",STR_PAD_LEFT) . chr(0);
  25.   $header .= str_pad(decoct(strlen($Data)),11,"0",STR_PAD_LEFT) . chr(0);
  26.   $header .= str_pad(decoct(time(0)),11,"0",STR_PAD_LEFT) . chr(0);
  27.   $header .= str_repeat(" ",8);
  28.   $header .= "0";
  29.   $header .= str_repeat(chr(0),100);
  30.   $header .= str_pad("ustar",6,chr(32));
  31.   $header .= chr(32) . chr(0);
  32.   $header .= str_pad($information["user_name"],32,chr(0));
  33.   $header .= str_pad($information["group_name"],32,chr(0));
  34.   $header .= str_repeat(chr(0),8);
  35.   $header .= str_repeat(chr(0),8);
  36.   $header .= str_repeat(chr(0),155);
  37.   $header .= str_repeat(chr(0),12);
  39.   // Compute header checksum
  40.   $checksum = str_pad(decoct(__computeUnsignedChecksum($header)),6,"0",STR_PAD_LEFT);
  41.   for($i=0; $i<6; $i++) {
  42.     $header[(148 + $i)] = substr($checksum,$i,1);
  43.   }
  44.   $header[154] = chr(0);
  45.   $header[155] = chr(32);
  47.   // Pad file contents to byte count divisible by 512
  48.   $file_contents = str_pad($Data,(ceil(strlen($Data) / 512) * 512),chr(0));
  50.   // Add new tar formatted data to tar file contents
  51.   $tar_file = $header . $file_contents;
  53.   return $tar_file;
  54. }
  56. function targz($Name, $Data)
  57. {
  58.   return gzencode(tarSection($Name,$Data),9);
  59. }

To use those functions all you have to do is send a header with the mime type for the tar gz ( application/x-gzip ) using the php header function. To add a tar/gz section for a file, read the file in an array using filegetcontents and pass the filename and data to the targz function. Echo what is returned. That’s it!

So why is it not active on clker.com website? I actually tried it and found that compression consumes a lot of CPU. In the first 20 minute I had more than one hundred connections for different users downloading their results and the CPU was saturated. This basically left no CPU for searching. So use it carefully, and only if you really need that functionality.

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Hardware problems – the mystery solved

Tuesday, December 11th, 2007

I previously wrote about hardware problems that were puzzling me, and I finally found the answer. I installed sensors on ubuntu and ran ksensors and just watched what’s going on. The old server that was shutting down suddenly had an opteron dual core processor, which ran at 50 degrees Celsius at no load. I had three websites running there, the most recent addition is clker.com . Due to the large number of people that were trying to access the website, the CPU was loaded and overheated, which inturn lead to it shutting down.

Of course the solution is to put the server in a very cold room, which I don’t have. I resorted to buying a new board and CPU, which does not heat as much as the old ones and transfered the database and pictures to it. Currently the no load temperature is 11 degrees, which I think is great. This new board is a special sale from microcenter, both the board and CPU were for $94 with $15 rebate Sempron 64! I added 1GB of RAM. It really worked much better than my expectations, as I had very very low performance expectations from that CPU

Currently this server is running clker.com only, and will run mibrahim.net today. The CPU load as shown in top does not pass 2% except in spikes. People are still digging as well as search engine robots. So that’s a good value if someone wants to run his/her own starter website.

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