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I learned something new today

Funny code comments

I read this on a website and just took some that appeared really funny to me.
* For the brave souls who get this far: You are the chosen ones,
* the valiant knights of programming who toil away, without rest,
* fixing our most awful code. To you, true saviors, kings of men,
* I say this: never gonna give you up, never gonna let you down,
* never gonna run around and desert you. Never gonna make you cry,
* never gonna say goodbye. Never gonna tell a lie and hurt you.

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Author: Prit -  Date: 22 Sep 2010 10:44
Tags: programming -  Visits: 93243 -  No Comments

Fossil SCM for Pritlog

SCM stands for Software Configuration Management.

I have been maintaining Pritlog versions using manual versioning. Recently, I started looking into moving Pritlog into a proper version control system for easier development and sharing

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Author: Prit -  Date: 02 Sep 2010 14:32
Tags: scm,programming -  Visits: 5597 -  No Comments

MongoDB - GridFS

Intro from the MongoDB website:

GridFS is a storage specification for large objects in MongoDB. It works by splitting large object into small chunks, usually 256k in size. Each chunk is stored as a separate document in a chunks collection. Metadata about the file, including the filename, content type, and any optional information needed by the developer, is stored as a document in a files collection.

So for any given file stored using GridFS, there will exist one document in files collection and one or more documents in the chunks collection.

GridFS links from the MongoDB website:


PHP MongoGridGS Class


I tested this out in PHP and following are some sample codes that may help.

1. PHP code to store uploaded file into the MongoDB GridFS.

if (isset($_POST["PHPSESSID"])) {

$conn = new Mongo(""); // Connect
$db = $conn->uniform_server; // Select DB
$db->authenticate("user","password"); // Authenticate to MongoDB
$grid = $db->getGridFS(); // Initialize GridFS
$name = $_FILES['Filedata']['name']; // Get Uploaded file name
$type = $_FILES['Filedata']['type']; // Try to get file extension
$id = $grid->storeUpload('Filedata',$name); // Store uploaded file to GridFS

/* Mime types did not work properly on my setup, hence the following logic */
$ext = substr($name,-3);
switch($ext) {
case "jpg": $type = "image/jpeg"; break;
case "gif": $type = "image/gif"; break;
case "png": $type = "image/png"; break;
case "txt": $type = "text/plain"; break;
case "pdf": $type = "application/pdf"; break;
case "zip": $type = "application/x-zip"; break;

/* Add additional metadata related to the file if required */
$files = $db->fs->files;
$files->update(array("filename" => $name), array('$set' => array("contentType" => $type, "aliases" => null, "metadata" => null)));

$conn->close(); // Close connection


2. PHP code to list all the files in the GridFS (in a particular database)

$conn = new Mongo(""); // Connect
$db = $conn->uniform_server; // Select DB
$db->authenticate("user","password"); // Authenticate to MongoDB
$grid = $db->getGridFS(); // Initialize GridFS

$cursor = $grid->find();

foreach ($cursor as $obj) { // iterate through the results
echo 'Filename: '.$obj->getFilename().' Size: '.$obj->getSize().'

$conn->close(); // Disconnect from Server

3. PHP code to download files stored in GridFS

$conn = new Mongo(""); // Connect
$db = $conn->uniform_server; // Select DB
$db->authenticate("user","password"); // Authenticate to MongoDB
$grid = $db->getGridFS(); // Initialize GridFS

$ask = $_REQUEST['file']; // Get filename requested

$file = $grid->findOne(array('filename' => $ask));
$files = $db->fs->files;
$file1 = $files->findOne(array('filename' => $ask));
$id = $file->file['_id'];

if ( (substr($ask,-3) == 'zip') || (substr($ask,-3) == 'pdf') ) {
/* Any file types you want to be downloaded can be listed in this */
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.$ask);
header('Content-Transfer-Encoding: binary');
$cursor = $db->fs->chunks->find(array("files_id" => $id))->sort(array("n" => 1));
foreach($cursor as $chunk) {
echo $chunk['data']->bin;
else {
header('Content-Type: '.$file1["contentType"]);
echo $file->getBytes();

$conn->close(); // Disconnect from Server

4. PHP code to delete a file from GridFS

$conn = new Mongo(""); // Connect
$db = $conn->uniform_server; // Select DB
$db->authenticate("user","password"); // Authenticate to MongoDB
$grid = $db->getGridFS(); // Initialize GridFS

$filename = $_REQUEST["file"]; // Get requested filename

$file = $grid->findOne($filename); // Find file in GridFS
$id = $file->file['_id']; // Get the files ID
$grid->delete($id); // Delete the file

$conn->close(); // Disconnect from Server

Author: Prit -  Date: 22 Jul 2010 12:13
Tags: mongodb,programming -  Visits: 55131 -  No Comments

MongoDB - Replica Pair

Intro from the MongoDB website:

Mongo supports a concept of replica pairs. These databases automatically coordinate which is the master and which is the slave at a given point in time.

At startup, the databases will negotiate which is master and which is slave. Upon an outage of one database server, the other will automatically take over and become master from that point on. In the event of another failure in the future, master status would transfer back to the other server. The databases manage this themselves internally.

You can read about the replica pair from the MongoDB website at the below link:

Following is an example of how to run a replica pair. A replica pair is different from the master-slave configuration. In a master slave config, the slave is read-only and acts like a backup database. In a replica pair, if any of the databases go down, then the other takes over as master.
./mongod --pairwith localhost:27018 --arbiter localhost:27019 --dbpath ~/data1
./mongod --port 27018 --pairwith localhost:27017 --arbiter localhost:27019 --dbpath ~/data2
./mongod --port 27019 #arbiter

The arbiter is a mongodb server that runs on a third machine that helps negitiate between the paired servers to determine which one should be master.

Following is the PHP example code to connect when using a replica pair:
$m = new Mongo("mongodb://localhost:27017,localhost:27018");

I tested this by stopping one server at a time and the other took over as master and the application continued to work without any failures or unavailability.
Author: Prit -  Date: 22 Jul 2010 12:07
Tags: mongodb,programming -  Visits: 5104 -  No Comments

MongoDB - Master Slave Setup

You can read more about the master-slave configuration at the MongoDB website:

Following commands to start a master slave setup in Ubuntu and monitor outputs if the logs are the same.
Start the master:
sudo /usr/bin/mongod --master --rest --config /etc/mongodb.conf

Start the slave:
sudo /usr/bin/mongod --rest --slave --source --dbpath /data/slavedb/ --fastsync --autoresync --config /etc/mongodb2.conf

Monitor logs from command line:
tail -f /var/log/mongodb/mongodb.log

Also, when I had authentication issues, the following webpage helped resolve:

In auth mode, for replication to work, you need to add the following kind of similar users to the "local" db of both the master and the slave.

Author: Prit -  Date: 22 Jul 2010 12:06
Tags: mongodb,programming -  Visits: 6160 -  No Comments

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