Objective-C

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. Objective-C

#import <CkoCache.h>
#import <NSString.h>

BOOL success = NO;

//  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.
CkoCache *cache = [[CkoCache alloc] init];

//  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 = [NSNumber numberWithInt:2];

//  Add some key/values to the persisted hash table (i.e. the cache).
//  The eTag is optional metadata.
NSString *key = @"apple";
NSString *eTag = @"";
NSString *itemValue = @"macos";
success = [cache SaveTextNoExpire: key eTag: eTag strData: itemValue];

//  Add more items..
success = [cache SaveTextNoExpire: @"microsoft" eTag: @"" strData: @"windows"];
success = [cache SaveTextNoExpire: @"google" eTag: @"" strData: @"android"];

//  Lookup items:
key = @"microsoft";
itemValue = [cache FetchText: key];
NSLog(@"%@%@%@",key,@": ",itemValue);

key = @"apple";
itemValue = [cache FetchText: key];
NSLog(@"%@%@%@",key,@": ",itemValue);