17. What is an exception log?
An exception log is a list of handled exceptions that occur while your
application is running. Reviewing the exception log periodically helps you
verify that exceptions are being handled correctly, are not occurring too
frequently, and are not preventing users from accomplishing tasks with your
application.
18. What is tracing and what are the advantages of using tracing
to log exceptions?
Tracing is a technique for recording events, such as exceptions, in an
application. There have always been ways to record errors in an application -
usually by opening a file and writing error messages to it. But tracing offers
the following significant advantages:
Standardization: Building tracing into the .NET Framework ensures
that programming techniques are the same across all the applications you
develop with the .NET Framework.
Built-in Web support:ASP.NET extends the .NET Framework
tools by including information related to the performance and behavior of Web
requests.
Configuration: You can turn tracing on and off using settings in your application’s
configuration file. You don’t have to recompile your application to enable or
disable tracing.
Performance:While disabled, tracing statements do not affect application
performance.
19. How do you turn tracing on and off for an ASP.NET web
application?
Tracing can be turned on or off for an entire Web application or for an
individual page in the application:
1. To turn tracing on for an entire application, in the application’s
Web.config file, set the trace element’s Enabled attribute to True.
Or
2. To turn tracing on for a single page, set the DOCUMENT object’s Trace
property to True in the Visual Studio .NET Properties window. This sets the @
Page directive’s Trace attribute to True in the Web form’s HTML.
20. Where is the trace output displayed by default?
By default, trace output is displayed at the end of each Web page. While
this is fine for debugging purposes, you’ll generally want to write trace
output to a log file when you start testing your completed application. To
write trace messages to a log file for an entire application, in the
application’s Web.config file, set the trace element’s PageOutput attribute
to False. ASP.NET then writes trace output to the Trace.axd file in your
application’s root folder.
21. How do you specify, how many page requets should be written
to the trace log?
The element's RequestLimit attribute can be used to specify how many
page requests to write to the trace log. For example, the following line from a
Web.config file turns on tracing for the application and writes the first 10
requests to the Trace.axd file.
22. How do you write trace messages to a log file for only
selected pages in an application?
To write trace messages to a log file for only selected pages in an application,
follow these steps: In the application’s Web.config file, set
the trace element’s Enabled attribute to True and PageOutput attribute
to False. For each Web page you want to exclude from tracing, set the @ Page
directive’s Trace attribute to False.
23. What is the difference between Trace.Write() and
Trace.Warn() methods of a trace object?
The Trace object provides the Write and Warn methods to allow you to
write messages to a request’s trace information. The two methods are identical
with one difference: messages written with Trace.Write are displayed in black,
whereas messages written with Trace.Warn are displayed in red.
24. How do you programmatically check if tracing is enabled?
The Trace object’s IsEnabled property can be used to programatically
check if tracing is enabled.
25. How do you prevent from trace output being written at the
bottom of the web page?
You can prevent from trace output being written at the bottom of the web
page by setting the trace element’s PageOutput attribute to False in the
Web.config file.
26. What is the name of the file to which trace log is written?
Trace.axd
27. Can you view Trace.axd from a remote machine?
No, by default, you can view Trace.axd only from the local server
running the application. If you want to view the trace log from a remote
machine, set the trace element’s LocalOnly attribute to False in the Web.config
file.
28. What is a transaction?
A transaction is a group of commands that change the data stored in a
database. The transaction, which is treated as a single unit, assures that the
commands are handled in an all-or-nothing fashion. if one of the commands
fails, all of the commands fail, and any data that was written to the database
by the commands is backed out. In this way, transactions maintain the integrity
of data in a database. ADO.NET lets you group database operations into
transactions.
29. What is the main purpose of database transactions?
The main purpose of database transactions is to maintain the integrity
of data in a database.
30. How do you determine which SQL commands are part of a
transaction?
You can determine what database commands belong in a transaction by
using the ACID test. Commands must be atomic, consistent, isolated, and
durable.
Commands belong in a transaction if they are:
Atomic: In other words, they make up a single unit of work. For example, if a
customer moves, you want your data entry operator to change all of the
customer’s address fields as a single unit, rather than changing street, then
city, then state, and so on.
Consistent: All the relationships between data in a database are maintained
correctly. For example, if customer information uses a tax rate from a state
tax table, the state entered for the customer must exist in the state tax
table.
Isolated: Changes made by other clients can’t affect the
current changes. For example, if two data entry operators try to make a change
to the same customer at the same time, one of two things occurs: either one
operator’s changes are accepted and the other is notified that the changes
weren’t made, or both operators are notified that their changes were not made.
In either case, the customer data is not left in an indeterminate state.
Durable: Once a change is made, it is permanent. If a system error or power
failure occurs before a set of commands is complete, those commands are undone
and the data is restored to its original state once the system begins running
again.
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