Integer problems and countermeasures when operating MongoDB with PHP_PHP tutorial

MongoDB itself has two integer types: 32-bit integers and 64-bit integers. However, the old version of the PHP driver treats all integers as 32-bit integers regardless of whether the operating system is 32-bit or 64-bit. As a result, 64-bit integers are processed Truncated. In order to solve this problem while maintaining compatibility as much as possible, the new version of PHP driver has added the mongo.native-long option, in order to treat integers as 64-bit in 64-bit operating systems. Interested Please refer to: 64-bit integers in MongoDB.

So does the PHP driver really completely solve the integer problem? NO! There are BUG when processing group operations:

To illustrate the problem, let’s first generate some test data:

Copy the code The code is as follows:

ini_set('mongo.native_long', 1);
$instance = new Mongo();
$instance = $instance->selectCollection('test', 'test');
for ($i = 0; $i < 10; $i++) {
$instance->insert(array(
'group_id' => rand(1, 5),
' count' => rand(1, 5),
));
}
?>

Let us use the group operation to group according to group_id and perform summary calculations count:

Copy code The code is as follows:

ini_set('mongo.native_long', 1 );
$instance = new Mongo();
$instance = $instance->selectCollection('test', 'test');
$keys = array('group_id' => 1 );
$initial = array('count' => 0);
$reduce = '
function(obj, prev) {
prev.count += obj.count;
}
';
$result = $instance->group($keys, $initial, $reduce);
var_dump($result);
?>

The result is different from what was expected. The count did not accumulate, but became [object Object]. Currently, if the group operation must be used, there are two methods to alleviate this problem:

Copy code The code is as follows:

ini_set('mongo.native_long', 0);
$initial = array('count' => ; (float)0);

These two methods are expedient measures that treat the symptoms rather than the root cause. Since there are problems with the implementation of group in the current PHP driver, then we will bypass it and use other To achieve the same function, this method is MapReduce:

Copy the code The code is as follows:

ini_set('mongo.native_long', 1);
$instance = new Mongo();
$instance = $instance->selectDB('test');
$map = '
function() {
emit(this.group_id, this.count);
}
';
$reduce = '
function(key, values) {
var sum = 0;
for (var index in values) {
sum += values[index];
}
return sum;
}
';
$result = $instance->command(array(
'mapreduce' => 'test',
'map' => $map,
'reduce' => $ reduce
));
$result = iterator_to_array($instance->{$result['result']}->find());
var_dump($result);
? >

It takes three steps to put an elephant in the refrigerator, but using MapReduce only requires two steps, Map and Reduce. Here is a PDF document that vividly illustrates the corresponding relationship between GROUP BY in MySQL and MapReduce in MongoDB:

SQL to MongoDB

In addition, there are many materials for reference, such as: MongoDB Aggregation III: Map-Reduce Basics.

Note: The software version is MongoDB (1.6.5), PECL Mongo (1.1.4). The conclusions may be different in different versions.

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