Invalidating query cache entries
To keep the query results for possible re-use, we need to make sure that the results directory is not deleted as part of query cleanup.Note that the Driver Context cleans up not only the query results directory but the parent directories of the results directory, which may complicate trying to save the query results directory while also performing the rest of the query cleanup.Many of the existing DBMS results caching solutions seem to cache results based on the query string.Unqualified table references need to be taken into account - depending on the current database at the time of the query, 2 queries running the exact same query string may access tables from completely different databases.
Caching query results allows a previously computed query result to be re-used in the event that the same query is processed by Hive.It also uses a Change Monitor object to monitor the state of the source data (which is a file) on the file system. Add(New Host File Change Monitor(file Paths)) ' Fetch the file contents. Read All Text("c:\cache\example.txt") cache.[Set]("filecontents", file Contents, policy) End If Label1. For example, the Memory Cache class has no dependencies on the .Private Sub btn Get_Click(By Val sender As Object, By Val e As Event Args) Dim cache As Object Cache = Memory Cache.[Default] Dim file Contents As String = Try Cast(cache("filecontents"), String) If file Contents Is Nothing Then Dim policy As New Cache Item Policy() Dim file Paths As New List(Of String)() file Paths. Text = file Contents End Sub Note The Memory Cache class is similar to the ASP. The Memory Cache class has many properties and methods for accessing the cache that will be familiar to you if you have used the ASP. The main differences between the Cache and Memory Cache classes are that the Memory Cache class has been changed to make it usable by . Therefore, when you call Memory Cache methods that implement base methods that contain a parameter for regions, do not pass a value for the parameter.Hive will need to check if the results for an incoming query are already saved in the results cache.A simple way to match the query with results cache entries would be to compare the incoming query text with the query text of the results cache entry.
If results caching is enabled, then Hive will need to make sure that the cache lookup works correctly in this case, or else it will have to be disabled for masking/filtering.