Unicode C

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. Unicode C

#include <C_CkCacheW.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkCacheW cache;
    const wchar_t *key;
    const wchar_t *eTag;
    const wchar_t *itemValue;

    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.
    cache = CkCacheW_Create();

    //  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.
    CkCacheW_AddRoot(cache,L"c:/temp/myCache");
    CkCacheW_putLevel(cache,2);

    //  Add some key/values to the persisted hash table (i.e. the cache).
    //  The eTag is optional metadata.
    key = L"apple";
    eTag = L"";
    itemValue = L"macos";
    success = CkCacheW_SaveTextNoExpire(cache,key,eTag,itemValue);

    //  Add more items..
    success = CkCacheW_SaveTextNoExpire(cache,L"microsoft",L"",L"windows");
    success = CkCacheW_SaveTextNoExpire(cache,L"google",L"",L"android");

    //  Lookup items:
    key = L"microsoft";
    itemValue = CkCacheW_fetchText(cache,key);
    wprintf(L"%s: %s\n",key,itemValue);

    key = L"apple";
    itemValue = CkCacheW_fetchText(cache,key);
    wprintf(L"%s: %s\n",key,itemValue);


    CkCacheW_Dispose(cache);

    }