Sets or returns the number of records retrieved from an ODBC data source that will be cached locally. Read/write Long.
Syntax
expression .CacheSize
expression A variable that represents a Recordset object.
Remarks
The value of the CacheSize property must be between 5 and 1200, but not greater than available memory will allow. A typical value is 100. A setting of 0 turns off caching.
Data caching improves performance if you use Recordset objects to retrieve data from a remote server. A cache is a space in local memory that holds the data most recently retrieved from the server; this is useful if users request the data again while the application is running. When users request data, the Microsoft Access database engine checks the cache for the requested data first rather than retrieving it from the server, which takes more time. The cache only saves data that comes from an ODBC data source.
Any Microsoft Access database engine-connected ODBC data source, such as a linked table, can have a local cache. To create the cache, open a
Recordset object from the remote data source, set the
CacheSize and
CacheStart properties, and then use the
FillCache method, or step through the records by using the
Move methods.
You can base the CacheSize property setting on the number of records your application can handle at one time. For example, if you're using a Recordset object as the source of the data to be displayed on screen, you could set its CacheSize property to 20 to display 20 records at one time.
The Microsoft Access database engine requests records within the cache range from the cache, and it requests records outside the cache range from the server.
Records retrieved from the cache don't reflect concurrent changes that other users made to the source data.
To force an update of all the cached data, set the CacheSize property of the Recordset object to 0, re-set it to the size of the cache you originally requested, and then use the FillCache method.
Example
This example uses the CreateTableDef and FillCache methods and the CacheSize, CacheStart and SourceTableName properties to enumerate the records in a linked table twice. Then it enumerates the records twice with a 50-record cache. The example then displays the performance statistics for the uncached and cached runs through the linked table.
Sub ClientServerX3()
Dim dbsCurrent As Database
Dim tdfRoyalties As TableDef
Dim rstRemote As Recordset
Dim sngStart As Single
Dim sngEnd As Single
Dim sngNoCache As Single
Dim sngCache As Single
Dim intLoop As Integer
Dim strTemp As String
Dim intRecords As Integer
' Open a database to which a linked table can be
' appended.
Set dbsCurrent = OpenDatabase("DB1.mdb")
' Create a linked table that connects to a Microsoft SQL
' Server database.
Set tdfRoyalties = _
dbsCurrent.CreateTableDef("Royalties")
' Note: The DSN referenced below must be set to
' use Microsoft Windows NT Authentication Mode to
' authorize user access to the Microsoft SQL Server.
tdfRoyalties.Connect = _
"ODBC;DATABASE=pubs;DSN=Publishers"
tdfRoyalties.SourceTableName = "roysched"
dbsCurrent.TableDefs.Append tdfRoyalties
Set rstRemote = _
dbsCurrent.OpenRecordset("Royalties")
With rstRemote
' Enumerate the Recordset object twice and record
' the elapsed time.
sngStart = Timer
For intLoop = 1 To 2
.MoveFirst
Do While Not .EOF
' Execute a simple operation for the
' performance test.
strTemp = !title_id
.MoveNext
Loop
Next intLoop
sngEnd = Timer
sngNoCache = sngEnd - sngStart
' Cache the first 50 records.
.MoveFirst
.CacheSize = 50
.FillCache
sngStart = Timer
' Enumerate the Recordset object twice and record
' the elapsed time.
For intLoop = 1 To 2
intRecords = 0
.MoveFirst
Do While Not .EOF
' Execute a simple operation for the
' performance test.
strTemp = !title_id
' Count the records. If the end of the
' cache is reached, reset the cache to the
' next 50 records.
intRecords = intRecords + 1
.MoveNext
If intRecords Mod 50 = 0 Then
.CacheStart = .Bookmark
.FillCache
End If
Loop
Next intLoop
sngEnd = Timer
sngCache = sngEnd - sngStart
' Display performance results.
MsgBox "Caching Performance Results:" & vbCr & _
" No cache: " & Format(sngNoCache, _
"##0.000") & " seconds" & vbCr & _
" 50-record cache: " & Format(sngCache, _
"##0.000") & " seconds"
.Close
End With
' Delete linked table because this is a demonstration.
dbsCurrent.TableDefs.Delete tdfRoyalties.Name
dbsCurrent.Close
End Sub