The Environment: Tuning for Performance in .NET Compose data matrix barcodes in .NET The Environment: Tuning for Performance

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The Environment: Tuning for Performance generate, create none none for none projects QR Codes Similarly, ret none none rieving long data such as large XML data, long varchar/text, long varbinary, Clobs, and Blobs can be problematic for memory. Suppose your application executes a query that retrieves hundreds of rows, and those rows happen to contain a Blob. If the database system does not support true LOBs, the database driver will probably emulate this functionality and retrieve the entire Blob across the network and place it in memory on the client.

See Data Retrieval, page 30, for more information. Avoid scrollable cursors unless you know your database system fully supports them Scrollable cursors let you go both forward and backward through a result set. Because of limited support for server-side scrollable cursors in many database systems, database drivers often emulate scrollable cursors, storing rows from a scrollable result set in memory on the client or application server.

Large scrollable result sets can easily consume memory. See Using Scrollable Cursors, page 36, for more information. If memory is a limiting factor on your database server, application server, or client, tune your database driver to compensate for that limiting factor Some database drivers provide tuning options that allow you to choose how and where some memory-intensive operations are performed.

For example, if your client excessively pages to disk because of large result sets, you may want to decrease the size of the fetch buffer, the amount of memory used by the driver to store results retrieved from the database server. Decreasing the fetch buffer size reduces memory consumption, but it means more network round trips, so you need to be aware of the trade-off. Disk When an operation reads or writes to disk, performance suffers because disk access is extremely slow.

The easiest way to avoid accessing the disk (or disk controller in the case of multiple disks) is to use memory. For example, consider the case of an application that retrieves large result sets. If your client or application server has ample memory and your database driver supports this tuning option, you could increase the size of the fetch buffer on the client to avoid the result set being written to disk.

However, remember that if you routinely stretch memory to its limit, paging to disk occurs more frequently. In addition to slowing performance, excessive paging can interfere with other processes that require the same disk, causing disk contention..

Hardware Disk contentio none for none n occurs when multiple processes or threads try to access the same disk simultaneously. The disk limits how many processes/threads can access it and how much data it can transfer. When these limits are reached, processes may have to wait to access the disk.

Often, CPU activity is suspended until disk access completes. If you suspect that disk access occurs more often than it should, the first thing you should do is rule out a memory bottleneck. Once you ve ruled out a memory bottleneck, make sure your application avoids unnecessary disk reads and writes so that disk contention rarely happens.

. Performance Ti p As a general rule, your application should only access the disk in the following cases: to retrieve database metadata into memory and to write changes to disk, such as in the case of committing transactions.. Table 4-5 lists some common causes for disk bottlenecks and their recommended solutions. Table 4-5 Cause Causes and Solutions of Disk Bottlenecks Solution Detect and res none for none olve the memory bottleneck. See Memory, page 107, for more information. Analyze and tune your application to avoid unnecessary disk reads or writes.

See Tuning Your Application to Avoid Unnecessary Disk Reads/Writes, page 112, for more information.. Excessive pagi ng caused by a memory bottleneck Excessive reads or writes to disk, possibly causing disk contention. Detecting Disk none for none Bottlenecks To detect a disk bottleneck, gather information about your system to answer the following questions: Is excessive paging occurring A memory bottleneck can resemble a disk bottleneck so it s important to rule out a memory problem before you make any disk improvements. See Detecting Memory Bottlenecks, page 108, for information about detecting memory bottlenecks..

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