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CHAPTER 10 MANAGED PROVIDERS OF DATA ACCESS
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cn.Open(); gvAuthors.DataSource = cm.ExecuteReader(); gvAuthors.DataBind(); cn.Close(); } This method bears about 110 requests per second. This improvement isn t much, and you may expect more because you ve moved away from dynamically generated SQL and are using stored procedures. However, the statements are not that complex, and the lion s share of the work is the actual sorting of the data. With this in mind, an improvement this size is almost surprising. This method is not very maintainable. Each of these stored procedures now has to be maintained. In a real application, the logic retrieving the data is going to be more complex than select * from a table. Any change to this logic will have to be propagated across all of these stored procedures. This is probably just not a reasonable, realistic solution. The real way to help this situation is to index all of the columns you re sorting by. Here, though, you re allowing the user to sort by all of the columns, and this many indexes is probably not a reasonable option. This is something to consider when designing an interface that enables users to pick what they sort by. It may be better to pick a subset of the columns that are most common to sort by and add indexes to those. The best thing to increase the performance of this page is going to be to cache the data in the memory of the web server, instead of going back to the database for it on each request. You already know that a data reader cannot be sorted, and you ve examined several strategies for doing the sorting at the database. Take a look at what happens when you move the data to the client. First, you ll pull that data access out into a helper method, centralizing the command and caching logic (see SortIE.aspx in Web10). private DataSet GetAuthors() { DataSet ds; ds = (DataSet)Cache["AuthorData"]; if (ds == null) { ds = new DataSet(); SqlConnection cn = new SqlConnection ("server=.;database=pubs;uid=sa;pwd=123123"); SqlCommand cm = new SqlCommand("select * from authors", cn); new SqlDataAdapter(cm).Fill(ds); Cache.Insert("AuthorData", ds); } return ds; }
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CHAPTER 10 MANAGED PROVIDERS OF DATA ACCESS
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Then you ll modify BindGrid to use the cached data from the DataSet instead of a data reader. You ll use the construction semantics of the DataView to apply the sort the user has requested (see SortIE.aspx in Web10). private void BindGrid(string sortExpr) { gvAuthors.DataSource = new DataView( GetAuthors().Tables[0], "", sortExpr, DataViewRowState.CurrentRows); gvAuthors.DataBind(); } This method yields an average of about 126 requests per second, but from the chart displayed in Figure 10-3, you can see this processing is really erratic. The server can handle about 145 requests per second; there are just consistent drops in the processing.
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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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