Perl

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. Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

# 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.
my $cache = Chilkat2::Cache->new;

# 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.
my $key = 'apple';
my $eTag = '';
my $itemValue = 'macos';
my $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);
print $key, ': ', $itemValue, "\n";

$key = 'apple';
$itemValue = $cache->FetchText($key);
print $key, ': ', $itemValue, "\n";