Francesco Altomare
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10967 Berlin (Germany)
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Website Performance: Meet Squid

Welcome back my advanced caching Reader,

Today we’ll present you the Squid. Squid is a very fast caching proxy program. Basically, it acts as an agent, accepting requests from clients (for example, browsers) and directing them to the fitting Internet Server. It keeps a copy of the returned data in an on-disk Cache. The genuine advantage of Squid emerges when the same information is requested multiple times, since a copy of the on-disk information is returned to the client, accelerating Internet access and saving bandwidth. A small amount of disk space can have a huge effect on bandwidth usage as well as browsing speed.
Internet Firewalls (which are usually used to protect Company or Personal Networks) often have a proxy component. So, what exactly makes Squid proxy different from a ordinary Firewall Proxy? To begin with, most Firewall Proxies don’t keep copies of the returned data, but rather they re-fetch requested data from the remote Server every time.
Squid is different from Firewall Proxies in other ways as well:
– Numerous Protocols are supported (Firewalls frequently have particular Proxies for particular Protocols making it hard to guarantee code security of a extensive program)
– Hierarchies of Proxies, arranged in complex connections are possible.
The Web consists of elements like HTML pages, graphics, sound files, etc. Since just a small piece of the Web is comprised of text, referring to all cached data as pages is wrong. Caches store objects, not pages.
Numerous Internet Servers support multiple Protocols. Per example, a Web Server utilizes the Hyper Text Transfer Protocol (HTTP) to serve data. An older protocol, the File Transfer Protocol (FTP) very frequently runs on the Servers, too. Muddling them up would be really bad. Per example, caching an FTP response and returning it to the client on a subsequent HTTP request would cause an error. Squid utilizes the whole URL to recognize everything kept in the cache.
To avoid returning outdated data to Clients, objects must be expired. Naturally, Squid has a way for dealing with this sort of things. It allows you to set refresh times for objects, thus ensuring that the outdated data isn’t returned to Clients.
Squid is based on Software created for the Harvest Project, which developed their “cached” as a side project. National Laboratory of Network Research (NLANR) has received funds for Squid development from the National Science Foundation (NSF). Squid is created as an Open Source Software, and in spite of the fact that development is done for the most part with NSF funding, features are added and bugs fixed by a team of online collaborators and enthusiasts.

“Why do we use Caches?”, he asked the Squid

Small Internet Service Providers (ISPs) cache to lessen their line costs, since a big part of their operating costs are related to Infrastructure, instead of being related to the Staff.
Companies and Content Providers (for example, AOL) have recently started to cache. These Companies are not having problems with shortage of bandwidth (without a doubt, they frequently have as much bandwidth as a small country), yet their Clients sometimes see slow responses or experience poor performance.
There are various reasons for this:

Origin Server Load
Raw bandwidth is nowadays expanding faster than overall Computer performance. Nowadays, numerous Servers act as a Back-end for one Site, load adjusting incoming requests. Where this is not conducted, the result is slow response. On the off chance that you have ever gotten a call complaining about slow response, you will know the advantage of caching – in numerous cases the User’s mind is already made up: it’s your shortcoming.

Quick Abort
Squid can be configured to keep fetching Objects (within certain size limits) even in spite of the fact that somebody who starts a download aborts it. Since there is a possibility of more than one individual wanting the same data, it’s useful to have an Object’s copy in your cache, even if the first User aborts his/her download. Where you have a lot of bandwidth, this continued-fetching ensures that there will be a local copy of the Object available, just on the off chance someone else needs it. This can drastically decrease latency, at the cost of higher bandwidth usage.

Peer Congestion
As bandwidth expands, Router speed needs to increase at the same rate. Numerous Peering Points (where enormous volumes of Traffic are exchanged) frequently don’t have the Router horsepower to support their perpetually increasing load. You can invest tremendous sums of money to upkeep the Network that stays in front of the growth curve, just to have all your efforts rendered useless the moment packets get off your network onto a big Peering Point, or onto another Service Provider’s Network.

Traffic spikes
Large sporting, television and political occasions can bring in a lot of Internet Traffic. Events like The Olympics, the Soccer World Cup, and the Starr report on the Clinton-Lewinsky issue create large Traffic spikes.
You can arrange everything before the sports events, but it’s hard to estimate the load that they will inevitably cause. If you are a local ISP, and a local team gets to the finals, you are prone to get an enormous peak in Traffic. Organizations can likewise be affected by Traffic spikes, with mass exchange of vast Databases or presentations flooding lines at random times. Though caching can’t totally take care of this problem, it can decrease the effect.

Inaccessible Sites
In the event that Squid tries to connect to an Origin Server, just to learn that it is down, it will log an error and return the Object (regardless of the possibility that there is a chance of sending out-of-date information to the Client) from disk. This decreases the effect of a large-scale Internet blackout, and can help when a backhoe digs up an important part of your Network backbone.

Districts with limited bandwidth
In many regions, bandwidth is expensive and latency is high, because of the very long haul links.

In numerous countries, or even in rural parts of industrialized countries, bandwidth may be expensive. Saving bandwidth decreases Internet infrastructural expenses significantly. Due to the fact that Internet connectivity is so costly, ISPs and their Customers diminish their bandwidth needs with caches.

In spite of the fact that reduction of latency is not regularly the real explanation behind introduction of caching in these areas, the issues experienced in the high bandwidth regions are exacerbated by the high latency and lower speed of the lines to those regions. Squid acts just as a HTTP-type proxy – it will act as a proxy for Browser-type Applications. As a rule, however, it won’t act as a Proxy for Applications other than Browsers. Squid is based on the HTTP/1.1 specification. Squid can only be a Proxy for programs that utilize this Protocol for Internet access. Browsers, for instance, use this specification; their primary function is the showcase of retrieved Web data, using the HTTP Protocol. FTP clients, then again, quite often support Proxy Servers, but don’t communicate with them using the HTTP Protocol. This means that these Clients won’t have the ability to understand the answers that Squid sends.

Inter-Cache Communication Protocols
Squid gives you the ability to share data between caches, but why would it be a good idea for you to do so?
Pretty much like there are benefits in connecting individual PCs to a Network, and that Network to the Internet, there are benefits in linking your cache to other individuals’ Networks of caches. So, the bigger your Client base, the more Objects requested, the higher chance of an Object being requested twice. To build up your hit rate, include more Clients.
On the other hand, quite often the size of your User base is limited – it’s limited by the number of Staff members or Clients. Co-operative Peering with different caches makes the size of your User base bigger, and viably increases your hit rate. If you peer with a large cache, you will find that the Objects’ rates your Clients are requesting are already available there. Many individuals can increase their hit rate by around 5% by peering with other caches. In the event that you own a large Network, one cache may not be able to handle all incoming requests. As opposed to needing to persistently upgrade one Machine, it makes sense to split the load between multiple Servers. This diminishes individual Server load, while increasing the overall number of queries your cache framework can deal with.


Thousands of Websites around the Internet use Squid to hugely enhance their content delivery and to keep original Servers safe for DDoS Attacks. Squid is likewise used for worldwide content delivery – copying only the content that is being requested, rather than copying everything from the original Server. Also, you can use Squid to route the traffic and balance requests by the Network of Webservers.

Local Proxies are very useful and help cope with the Technology growth by effectively quadrupling the capacity of the Servers behind them. What do you think about caching Proxies like Squid? Tell us all about it in the comments.

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