Varnish Caching System with Php
Varnish is an open source HTTP accelerator designed for content-heavy dynamic web sites. Varnish Cache is really, really fast. It typically speeds up delivery with a factor of 300 - 1000x, depending on your architecture. A high level overview of what Varnish does can be seen in the video attached to this web page.
Varnish stores data in virtual memory and leaves the task of deciding what is stored in memory and what gets paged out to disk to the operating system. This helps avoid the situation where the operating system starts caching data while they are moved to disk by the application.
The principal configuration mechanism is VCL (Varnish Configuration Language), a domain-specific language (DSL) used to write hooks which are called at critical points in the handling of each request. Most policy decisions are left to VCL code, making Varnish far more configurable and adaptable than most other HTTP accelerators. When a VCL script is loaded, it is translated to C, compiled to a shared object by the system compiler, and linked directly into the accelerator.
Varnish supports load balancing using both a round-robin and a random director, both with a per-backend weighting. Basic health-checking of backends is also available.
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Varnish Magento Extension