laravel游标和laravel chunk方法有什么区别？

I would like to know what is the difference between laravel chunk and laravel cursor method. Which method is more suitable to use? What will be the use cases for both of them? I know that you should use cursor to save memory but how it actually works in the backend?

A detailed explanation with example would be useful because I have searched on stackoverflow and other sites but I didn't found much information.

Here is the code snippet's from the laravel documentation.

Chunking Results

Flight::chunk(200, function ($flights) {
    foreach ($flights as $flight) {
        //
    }
});

Using Cursors

foreach (Flight::where('foo', 'bar')->cursor() as $flight) {
    //
}

Indeed This question might attract some opinionated answer, however the simple answer is here in Laravel Docs

Just for reference:

This is chunk:

enter image description here

This is Cursor:

enter image description here

Chunk retrieves the records from the database, and load it into memory while setting a cursor on the last record retrieved so there is no clash.

So the advantage here is if you want to reformat the large record before they are sent out, or you want to perform an operation on an nth number of records per time then this is useful. An example is if you are building a view out/excel sheet, so you can take the record in counts till they are done so that all of them are not loaded into the memory at once and thereby hitting the memory limit.

Cursor uses PHP Generators, you can check the php generators page however here is an interesting caption:

enter image description here

While I cannot guarantee that I understand fully the concept of Cursor, but for Chunk, chunk runs the query at every record size, retrieving it, and passing it into the closure for further works on the records.

Hope this is useful.

chunk is based on pagination, it maintains a page number, and do the looping for you.

For example, DB::table('users')->select('*')->chunk(100, function($e) {}) will do multiple queries until the result set is smaller than the chunk size(100):

select * from `users` limit 100 offset 0;
select * from `users` limit 100 offset 100;
select * from `users` limit 100 offset 200;
select * from `users` limit 100 offset 300;
select * from `users` limit 100 offset 400;
...

cursor is based on PDOStatement::fetch and Generator.

$cursor = DB::table('users')->select('*')->cursor()
foreach ($cursor as $e) { }

will do issue a single query:

select * from `users`

But the driver doesn't fetch the result set at once.

I made some benchmark using cursor and where

foreach (\App\Models\Category::where('type','child')->get() as $res){

}

foreach (\App\Models\Category::where('type', 'child')->cursor() as $flight) {
    //
}

return view('welcome');

here is the result: chunk is faster thank using where

We have a comparison: chunk() vs cursor()

  • cursor(): High Speed
  • chunk(): Constant Memory Usage

10,000 records:

+-------------+-----------+------------+
|             | Time(sec) | Memory(MB) |
+-------------+-----------+------------+
| get()       |      0.17 |         22 |
| chunk(100)  |      0.38 |         10 |
| chunk(1000) |      0.17 |         12 |
| cursor()    |      0.16 |         14 |
+-------------+-----------+------------+

100,000 records:

+--------------+------------+------------+
|              | Time(sec)  | Memory(MB) |
+--------------+------------+------------+
| get()        |        0.8 |     132    |
| chunk(100)   |       19.9 |      10    |
| chunk(1000)  |        2.3 |      12    |
| chunk(10000) |        1.1 |      34    |
| cursor()     |        0.5 |      45    |
+--------------+------------+------------+
  • TestData: users table of Laravel default migration
  • Homestead 0.5.0
  • PHP 7.0.12
  • MySQL 5.7.16
  • Laravel 5.3.22