PowerBuilder

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. PowerBuilder

integer li_rc
long li_Success
oleobject loo_Cache
string ls_Key
string ls_ETag
string ls_ItemValue

li_Success = 0

//  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.
loo_Cache = create oleobject
li_rc = loo_Cache.ConnectToNewObject("Chilkat.Cache")
if li_rc < 0 then
    destroy loo_Cache
    MessageBox("Error","Connecting to COM object failed")
    return
end if

//  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.
loo_Cache.AddRoot("c:/temp/myCache")
loo_Cache.Level = 2

//  Add some key/values to the persisted hash table (i.e. the cache).
//  The eTag is optional metadata.
ls_Key = "apple"
ls_ETag = ""
ls_ItemValue = "macos"
li_Success = loo_Cache.SaveTextNoExpire(ls_Key,ls_ETag,ls_ItemValue)

//  Add more items..
li_Success = loo_Cache.SaveTextNoExpire("microsoft","","windows")
li_Success = loo_Cache.SaveTextNoExpire("google","","android")

//  Lookup items:
ls_Key = "microsoft"
ls_ItemValue = loo_Cache.FetchText(ls_Key)
Write-Debug ls_Key + ": " + ls_ItemValue

ls_Key = "apple"
ls_ItemValue = loo_Cache.FetchText(ls_Key)
Write-Debug ls_Key + ": " + ls_ItemValue


destroy loo_Cache