Squid and cache digest configuration in .NET Integrating QR Code JIS X 0510 in .NET Squid and cache digest configuration

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8. using none toincoporate none in web,windows application Bar code to 2D Code Squid and cache digest configuration To be able to use c ache digests, we must enable cache digests using the --enable-cachedigests option with the configure program before compiling Squid. Let"s have a look at the cache digest related directives available in the Squid configuration file..

Digest generation I none for none t makes sense to generate cache digests only when we plan to use cache digests for peer communication. Therefore, we can use the digest_generation directive in the configuration file to select whether the digest will be generated or not. The possible values for this directive can be on or off.

By default, this directive is set to on and Squid generates cache digests. Digest bits per entry The data structure, Bloom Filter, which is used to build cache digest, provides a lossy encoding and there may be false hits even in the cache digests. The directive digest_bits_ per_entry determines the number of bits that will be used for encoding one single entry or a cached object.

The larger value of bits per entry will result in higher accuracy and hence lesser false hits, but will this consume more space in the main memory and more bandwidth while transferring over the network. The default value of digest_bits_per_entry is 5 but we can safely push it to 7 for more accuracy if we have a large cache. Digest rebuild period We can use the directive digest_rebuild_period to set the time interval, after which the cache digest will be rebuilt.

One hour is the default, which will result in a not so up-todate cache digest, but rebuilding a cache digest is a CPU-intensive job and this time interval should be set depending on the hardware capabilities and load on the proxy server. We can safely set it to 10 or 15 minutes to keep things fresh..

Digest rebuild peri od implies the time after which the cache digest will be rebuilt in memory. This time doesn"t imply the time after which the cache digest will be written to disk..

Digest rebuild chun none none k percentage The directive digest_rebuild_chunk_percentage determines the percentage of the cache which will be added to the cache digest every time the rebuild routine is called on schedule. The default behavior is to add 10 percent of the cache to the cache digest every rebuild. Digest swapout chunk The amount or number of bytes of the cache digest that will be written to the disk at a time is determined by the directive digest_swapout_chunk.

The default behavior is to write 4096 bytes at a time.. [ 217 ]. Building a Hierarchy of Squid Caches Digest rewrite peri od The digest rewrite period is the time interval after which the cache digest is written to disk, which then can be served to other peers. We can configure this time interval using the digest_rewrite_period directive. Generally, it should be equal to digest the rebuild period.

. Hypertext Caching Protocol HTCP or Hypertext C aching Protocol is similar to ICP but has advanced features and generally results in better performance compared to the ICP protocol. Both the ICP and HTCP protocols use UDP for communication and TCP communication is optionally allowed for HTCP for protocol debugging. HTCP has the following advantages over the ICP protocol: ICP queries include only URI while HTCP queries include full HTTP headers.

HTCP also includes HTTP headers in a request, which helps the server avoid false hits, but would be true only for a URL key and would be false if more headers are known. HTCP allows third party replies, using which a peer can inform us about an alternate location of a cached object. ICP doesn"t have a similar provision.

HTCP supports monitoring of peers for cache additions or deletions while ICP doesn"t. HTCP uses a variable sized binary message format, which can be used for extending the protocol, while ICP uses a fixed size binary message format rendering ICP to be very difficult to extend. HTCP provides optional message authentication using shared secret keys while ICP doesn"t.

For more details on the HTCP protocol, please visit

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