AutoIt

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. AutoIt

Local $bSuccess = 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.
$oCache = ObjCreate("Chilkat.Cache")

; 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.
$oCache.AddRoot "c:/temp/myCache"
$oCache.Level = 2

; Add some key/values to the persisted hash table (i.e. the cache).
; The eTag is optional metadata.
Local $sKey = "apple"
Local $sETag = ""
Local $sItemValue = "macos"
$bSuccess = $oCache.SaveTextNoExpire($sKey,$sETag,$sItemValue)

; Add more items..
$bSuccess = $oCache.SaveTextNoExpire("microsoft","","windows")
$bSuccess = $oCache.SaveTextNoExpire("google","","android")

; Lookup items:
$sKey = "microsoft"
$sItemValue = $oCache.FetchText($sKey)
ConsoleWrite($sKey & ": " & $sItemValue & @CRLF)

$sKey = "apple"
$sItemValue = $oCache.FetchText($sKey)
ConsoleWrite($sKey & ": " & $sItemValue & @CRLF)