Go

Large Persistent Hash Table Stored on Filesystem

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Demonstrates how to implement a large, persistent hash table that is stored on the filesystem and allows for quick retrieval using a hash key. Go

    success := false

    // Let's say we would like to implement a persistent hash table with approximately 200,000 entries.
    // We want something simple and straightforward.
    // 
    // The Chilkat Cache class is a solution that might fit.
    // 
    // Each hash table entry is a file.  Depending on the number of anticipated hash entries,
    // the files can be contained in a single directory, or a collection of 256 directories,
    // or a collection of 256x256 directories.

    // There are 3 options:
    // 
    // Level 0: All cache files are in a single directory (the cache root).
    // Level 1: Cache files are located in 256 sub-directories numbered 0 .. 255 directly under the cache root.
    // Level 2: There are two levels of sub-directories under the cache root. 
    //          The 1st level has 256 sub-directories numbered 0 .. 255 directly under the cache root. 
    //          The 2nd level allows for up to 256 sub-directories (0..255) under each level-1 directory. 
    //          Cache files are stored in the leaf directories. 

    // For this example, given that we anticipate a larger number of hash entries, we choose a "level 2" cache.
    cache := chilkat.NewCache()

    // We can also spread the cache among several root directories, but for this example we'll only use one root directory.
    // Call AddRoot once for each root directory.
    cache.AddRoot("c:/temp/myCache")
    cache.SetLevel(2)

    // Add some key/values to the persisted hash table (i.e. the cache).
    // The eTag is optional metadata.
    key := "apple"
    eTag := ""
    var itemValue *string = new(string)
    *itemValue = "macos"
    success = cache.SaveTextNoExpire(key,eTag,*itemValue)

    // Add more items..
    success = cache.SaveTextNoExpire("microsoft","","windows")
    success = cache.SaveTextNoExpire("google","","android")

    // Lookup items:
    key = "microsoft"
    itemValue = cache.FetchText(key)
    fmt.Println(key, ": ", *itemValue)

    key = "apple"
    itemValue = cache.FetchText(key)
    fmt.Println(key, ": ", *itemValue)

    cache.DisposeCache()