Log File

[Peter J. Holzer]

On 2023-05-31 00:22:11 -0700, ahsan iqbal wrote:
> Why we need a log file ?

A log file contains information about what your program was doing. You
use it to check that your program was performing as intended after the
fact. This is especially useful for tracking down problems with programs
which are either long-running or are running unattended.

For example, if a user tells me that they were having a problem
yesterday evening I can read the log file to see what my program was
doing at the time which will help me to pin down the problem.

The important part to remember is that a log file will only contain
information the program writes. If you didn't think to log some
information then it won't be in the log file and you can't look it up
afterwards. On the other hand you don't want to log too much information
because that might cause performance problems, it might fill up your
disks and it will be a chore to find the relevant information in a sea
of irrelevant details. So deciding what to log is a bit of an art.

> If i read a large text file than how log file help me in this regard?

It won't help you with reading the file.

However, you might want to log some information about operation, e.g.
when you started (log files usually contain time stamps), when you
ended, how large the file was, etc. That way you can compare different
runs (has the file increased in size over the last month? Was reading
especially slow yesterday?). You could also log a status message every
once in a while (e.g. every 100 MB or every 100000 lines). That will
give you reassurance that the program is working and a rough estimate
when it will be finished. Or you can log any other information you think
might be useful.

        hp

-- 
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | hjp at hjp.at         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"
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