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Figure 10-3. Results per second when caching data and sorting with a DataView The problem is the number of allocations you re making to the managed heap. Every time a request occurs, you re allocating a DataView to the heap. With all the requests coming in, this forces the garbage collector to do frequent sweeps and reclaim the memory you ve used for previous requests. This leads to the up and down peak load the server can handle. Instead of creating a view for each user, you ll want to get more aggressive in the use of the cache. In this version, you ll cache each DataView; thus, all users will share the same instance of the DataView, and there will only be one per sort in the cache (see SortIE.aspx in Web10). private void BindGrid(string sortExpr) { DataView dv; string sCacheEntry = string.Format("Author_Sort_{0}", sortExpr); dv = (DataView)Cache[sCacheEntry];

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eval : Map<Var,bool> -> Prop -> bool support : Prop -> Set<Var> cases : 'a list -> seq<Map<'a,bool>> truthTable : Prop -> seq<Map<Var,bool> * bool> satisfiable : Prop -> bool tautology : Prop -> bool tautologyWithCounterExample : Prop -> Map<Var,bool> option printCounterExample : #seq<'a> option -> unit

In this chapter, you ll learn what LOBs (large objects) are and how they re stored in Oracle. You ll then examine how to retrieve and manipulate them. You ll also compare various alternatives when manipulating LOBs through the JDBC API.

The function eval computes the value of a formula given assignments for each of the variables that occurs in the formula. support simply computes the set of variables that occurs in the formula. You can now use these functions to examine truth tables for some simple formulae, though first you may want to define the following functions to display truth tables neatly in F# Interactive: let stringOfBit b = (if b then "T" else "F") let stringOfEnv env = Map.fold(fun k v acc -> sprintf "%s=%s;" k (stringOfBit v)+acc) env "" let stringOfLine (env,res) = sprintf "%20s %s" (stringOfEnv env) (stringOfBit res) let stringOfTruthTable tt = "\n" + (tt |> Seq.to_list |> List.map stringOfLine |> String.concat "\n") Here are the truth tables for x, x AND y, and x OR NOT(x) : > fsi.AddPrinter(fun tt -> tt |> Seq.truncate 20 |> stringOfTruthTable);; > truthTable (var "x");; > val it : seq<Map<Var,bool> * bool> = x=F; F x=T; T > truthTable (var "x" &&& var "y");; > val it : seq<Map<Var,bool> * bool> = x=F;y=F; F x=F;y=T; F x=T;y=F; F x=T;y=T; T > truthTable (var "x" ||| ~~~(var "x"));; > val it : seq<Map<Var,bool> * bool> = x=F; T x=T; T

In this chapter, you ll learn about statement caching, its different flavors in JDBC, and how it improves the performance of JDBC programs. As a background to the statement-caching concept, you ll also examine cursors and ref cursors in detail. In addition, you ll look at two other related caches Oracle provides you with: the PL/SQL cursor cache (which is the PL/SQL equivalent of the JDBC statement cache) and session cached cursors.

if (dv == null) { dv = new DataView( GetAuthors().Tables[0], "", sortExpr, DataViewRowState.CurrentRows); Cache.Insert(sCacheEntry, dv); } gvAuthors.DataSource = dv; gvAuthors.DataBind(); } Here, you get 136 requests per second, making this the best performing option. This also consumes fewer resources than the previous example, as you only have one DataView per sort instead of one per request. In-memory filtering of the data is another example of a task that the DataSet and DataViews are particularly suited for. Again, you could implement this at the database tier, but if you re giving the user control over the column they re querying on, once again you re looking at having to use dynamic SQL generation. Sorting on a column using a DataView causes the DataView to index that column under the hood, so you get an optimized structure for applying the filter. For this example, you ll display a list of states, and when the user selects one, display a grid of the authors from that state. You ll once again use a DropDownList and a GridView (the code for this demo can be found in Filtering.aspx of the Web10 project). <asp:DropDownList Runat=server ID=ddlState AutoPostBack="True" OnSelectedIndexChanged="ddlState_SelectedIndexChanged" /> <asp:GridView Runat=server ID=gvAuthors EnableViewState=False BorderWidth="1px" BackColor="LightGoldenrodYellow" GridLines="None" CellPadding="2" BorderColor="Tan" ForeColor="Black"> <FooterStyle BackColor="Tan" /> <PagerStyle ForeColor="DarkSlateBlue" HorizontalAlign="Center" BackColor="PaleGoldenrod" /> <HeaderStyle Font-Bold="True" BackColor="Tan" /> <AlternatingRowStyle BackColor="PaleGoldenrod" /> <SelectedRowStyle ForeColor="GhostWhite" BackColor="DarkSlateBlue" /> </asp:GridView>

We invoke the procedure to add an e-mail address to the department number 10: benchmark@ORA10G> exec add_email_address( 10, 'new_contact@mycompany.com') PL/SQL procedure successfully completed. We run a query to verify that the update went through successfully: benchmark@ORA10G> select a.column_value 2 from dep_email_addresses c, TABLE(c.email_addresses) a 3 where dep_no=10; king@mycompany.com joe@mycompany.com john@mycompany.com new_contact@mycompany.com Next, we ll take a quick peek at how Oracle internally stores a varray column.

From this you can see that x OR NOT(x) is a tautology, since it always evaluates to TRUE regardless of the value of the variable x.