Zig

Large Persistent Hash Table Stored on Filesystem

See more Misc Examples

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

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // 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.
    const cache = try chilkat.Cache.init();
    defer cache.deinit();

    // 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.
    var key: [:0]const u8 = "apple";
    const e_tag = "";
    var item_value: [:0]const u8 = "macos";
    try cache.saveTextNoExpire(key, e_tag, item_value);

    // Add more items..
    try cache.saveTextNoExpire("microsoft", "", "windows");
    try cache.saveTextNoExpire("google", "", "android");

    // Lookup items:
    key = "microsoft";
    item_value = try cache.fetchText(alloc, key);
    std.debug.print("{s}: {s}\n", .{ key, item_value });

    key = "apple";
    item_value = try cache.fetchText(alloc, key);
    std.debug.print("{s}: {s}\n", .{ key, item_value });
}