Why do replace() before set() in Memcache?

Question

symfony

Understanding the Memcache library for PHP, I came across an interesting comment : before doing set() of a value that could already exist, you need to do replace() , because ostensibly when working with a cluster of memcached servers, set() can set several values ​​​​with the same keys (on different nodes, I guess), and then get can return any of these values.
In order to avoid problems, the author suggests using the following code:

$result = $memcache->replace($key, $var); <br>
if( $result == false ) <br>
{ <br>
    $result = $memcache->set($key, $var); <br>
} <br>

This approach is widely used, for example, it can be found in the memcached wrapper in symfony .
I can imagine how values ​​\u200b\u200bwith the same keys can appear in different nodes, but why set () is to blame for this duplication of keys and how replace () can save from this - at least kill I don’t understand.
How do you think this can happen? What is the fundamental difference between set() and replace() in this context?

Answer 1

Are you talking about Memcache or Memcache d ? These are different libraries and Memcache really has some kind of glitch with setters. Try memcached.

Answer 2

clack clack