ajp_cache_lock
The ajp_cache_lock directive prevents multiple simultaneous requests for the same URI from being proxied to the AJP server, reducing load and duplicative processing.
Description
The ajp_cache_lock directive is utilized within the AJP (Apache Jserv Protocol) module of NGINX to coordinate requests made to the AJP backend. When enabled, if a request for a specific URI is currently being processed, subsequent identical requests will be held until the first request is completed. This locking mechanism helps to prevent excessive load on the AJP server that can occur when many concurrent requests are made for the same resource, which could lead to redundant processing and increased latency. The directive is particularly useful in scenarios with high traffic where cache misses may prompt numerous requests simultaneously, ensuring that the backend is not overwhelmed by processing duplicate requests.
The directive accepts a flag as its argument. It is typically set to either on or off, where turning it on enables the locking behavior and off disables it. When ajp_cache_lock is set to on, NGINX will ensure that only one request for the same cache key is passed to the backend server while simultaneous requests are queued, improving efficiency and reducing resource contention on the backend servers. Furthermore, if a request is completed and a successful response is received, subsequent requests will be able to utilize the cached response immediately, lowering response times for users requesting the same resource after the cache is populated.
Config Example
http {
upstream my_backend {
server 127.0.0.1:8009;
}
server {
listen 80;
location / {
ajp_pass my_backend;
ajp_cache_lock on;
}
}
}Ensure that enabling ajp_cache_lock does not result in high request queuing leading to increased latency for end users.
Verify that your backend AJP server is capable of handling request locks properly and does not timeout before the first request completes.