(Node.js) Large Persistent Hash Table Stored on Filesystem

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

Install Chilkat for Node.js and Electron using npm at Chilkat npm packages for Node.js Chilkat npm packages for Electron on Windows, Linux, MacOSX, and ARM

var os = require('os');
if (os.platform() == 'win32') {  
    if (os.arch() == 'ia32') {
        var chilkat = require('@chilkat/ck-node21-win-ia32');
    } else {
        var chilkat = require('@chilkat/ck-node21-win64'); 
    }
} else if (os.platform() == 'linux') {
    if (os.arch() == 'arm') {
        var chilkat = require('@chilkat/ck-node21-arm');
    } else if (os.arch() == 'x86') {
        var chilkat = require('@chilkat/ck-node21-linux32');
    } else {
        var chilkat = require('@chilkat/ck-node21-linux64');
    }
} else if (os.platform() == 'darwin') {
    if (os.arch() == 'arm64') {
        var chilkat = require('@chilkat/ck-node21-mac-m1');
    } else {
        var chilkat = require('@chilkat/ck-node21-macosx');
    }
}

function chilkatExample() {

    // 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";
    var 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();