2019-01-12 14:06:22 | 作者: 敬曦 | 标签: | 浏览: 2317
Every cursor uses temporary resources to hold its data. These resources can be memory, a disk paging file, temporary disk files, or even temporary storage in the database. The cursor is called a client-side cursor when these resources are located on the client machine. The cursor is called a server-side cursor when these resources are located on the server machine.Client-Side Cursors
With a non-keyset client-side cursor, the server sends the entire result set across the network to the client machine. The client machine provides and manages the temporary resources needed by the cursor and result set. The client-side application can browse through the entire result set to determine which rows it requires.
Static and keyset-driven client-side cursors may place a significant load on your workstation if they include too many rows. While all of the cursor libraries are capable of building cursors with thousands of rows, applications designed to fetch such large rowsets may perform poorly. There are exceptions, of course. For some applications, a large client-side cursor may be perfectly appropriate and performance may not be an issue.
One obvious benefit of the client-side cursor is quick response. After the result set has been downloaded to the client machine, browsing through the rows is very fast. Your application is generally more scalable with client-side cursors because the cursors resource requirements are placed on each separate client and not on the server.Server-Side Cursors
With a server-side cursor, the server manages the result set using resources provided by the server machine. The server-side cursor returns only the requested data over the network. This type of cursor can sometimes provide better performance than the client-side cursor, especially in situations where excessive network traffic is a problem.
Server-side cursors also permit more than one operation on the connection. That is, once you create the cursor, you can use the same connection to make changes to the rows — without having to establish an additional connection to handle the underlying update queries.
However, its important to point out that a server-side cursor is — at least temporarily — consuming precious server resources for every active client. You must plan accordingly to ensure that your server hardware is capable of managing all of the server-side cursors requested by active clients. Also, a server-side cursor can be slow because it provides only single row access — there is no batch cursor available.
Server-side cursors are useful when inserting, updating, or deleting records. With server-side cursors, you can have multiple active statements on the same connection. With SQL Server, you can have pending results in multiple statement handles.
Advantages to using server-side cursors include those in the following list.