Node.js

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. Node.js

NODEJS_PRELUDE

function chilkatExample() {

    var 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.
    var cache = new chilkat.Cache();

    //  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.Level = 2;

    //  Add some key/values to the persisted hash table (i.e. the cache).
    //  The eTag is optional metadata.
    var key = "apple";
    var eTag = "";
    var 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);
    console.log(key + ": " + itemValue);

    key = "apple";
    itemValue = cache.FetchText(key);
    console.log(key + ": " + itemValue);

}

chilkatExample();