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If I need to retrieve a large string from a DB, Is it faster to search for it using the string itself or would I gain by hashing the string and storing the hash in the DB as well and then search based on that?
If yes what hash algorithm should I use (security is not an issue, I am looking for performance)
If it matters: I am using C# and MSSQL2005
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Hashing is a cryptographic process that can be used to validate the authenticity and integrity of various types of input. It is widely used in authentication systems to avoid storing plaintext passwords in databases, but is also used to validate files, documents and other types of data.
Hashing is the process of transforming any given key or a string of characters into another value. This is usually represented by a shorter, fixed-length value or key that represents and makes it easier to find or employ the original string. The most popular use for hashing is the implementation of hash tables.
Hashing is one of the algorithms which calculates a string value from a file, which is of a fixed size. Basically, it contains blocks of data, which is transformed into a short fixed-length key or value from the original string. Usually, a summary of the information or data within that sent file.
NO! A hash code is not an id, and it doesn't return a unique value. This is kind of obvious, when you think about it: GetHashCode returns an Int32 , which has “only” about 4.2 billion possible values, and there's potentially an infinity of different objects, so some of them are bound to have the same hash code.
Are you doing an equality match, or a containment match? For an equality match, you should let the db handle this (but add a non-clustered index) and just test via WHERE table.Foo = @foo. For a containment match, you should perhaps look at full text index.
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