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(Unicode C) Large Persistent Hash Table Stored on FilesystemDemonstrates how to implement a large, persistent hash table that is stored on the filesystem and allows for quick retrieval using a hash key.
#include <C_CkCacheW.h> void ChilkatSample(void) { HCkCacheW cache; const wchar_t *key; const wchar_t *eTag; const wchar_t *itemValue; BOOL success; // 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); } |
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