ISPPlanet Cache Review Series - Squid 2.3

Tuning Cache Efficiency
Once you've stabilized Squid, you can then proceed to fine-tune its operating efficiency. The config file contains over 100 tuning knobs. Among other things, you can:

• modify listening ports, IP addresses, hostnames, and connect, select, request, and ident timeouts
• modify outgoing ports to spread response handling across multiple interfaces
• specify ICP ports, neighbor selection criteria (including weight and TTL), and cache digests
• set cache swap high and low water marks for cache object replacement
• limit the largest object size or prevent caching based on URL substrings
• determine the location, size, and index levels for cache storage configure the size and refresh behavior for the IP and FQDN (DNS) caches
• enable and configure memory pools to increase speed
• enable and configure delay pools to constrain bandwidth
• set maximum HTTP request and reply body and header sizes to protect against DOS attacks
• define min / max lifetimes for objects without TTL, identified by URL regular expression
• choose a replacement policy (see below)

Squid can't provide the patented adaptive or predictive refresh methods used by some commercial caching products, and doesn't include the ability to preload specified high-utilization sites. However, it is quite simple to write a script that uses wget to download sites, invoked on a scheduled basis by cron.

You'll find a tuning tips to increase hit rate, improve response time, and optimize cache performance in the Squid FAQ. The Cache Manager offers instantaneous, tabular stats. General Runtime Info summarizes HTTP, ICP, and DNS request rates, hit ratios, median service times, mean object size, CPU, memory, swap, and file descriptor usage.

Many stats are summarized over the past five minutes and hour. Further detail is provided for memory and cache utilization, DNS (IP and FQDN) cache content and stats, store directory stats (right), and objects that are in memory, in transit, or being swapped out. Peer selection algorithms, stats, and digest info monitor hierarchy performance. Header and refresh stats, traffic counters, and server-side histograms show how hard Squid is working to retrieve content.

 

The client list (left), client-side active requests, persistent connection utilization, and authenticator stats summarize request activity. It takes time to find what you're looking for and get comfortable with interpreting the voluminous data presented here.

Introduction/Open Source	ACLs and Authentication
Software Installation	Squid Resource Usage <
Managing Squid	Tuning Cache Efficiency
Deploying Squid	> Monitoring Squid
Maintenance and Support/Final Words