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But the asynchronous, event-driven approach still has a problem. Or, as I like to think of it, an “enemy”. And the name of the enemy is: blocking. Unfortunately, many third-party modules use blocking calls, and users (and sometimes even the developers of the modules) aren’t aware of the drawbacks. Blocking operations can ruin NGINX performance and must be avoided at all costs.

Even in the current official NGINX code it’s not possible to avoid blocking operations in every case, and to solve this problem the new “thread pools” mechanism was implemented in NGINX version 1.7.11. What it is and how it supposed to be used, we will cover later. Now let’s meet face to face with our enemy.
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