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ASP CGI And PHP Scripts And Record Locking What Every Webmaster Needs To Know
any of us install
server-side (ASP, CGI or 1. Follow-up autoresponders
PHP) scripts on our web typically store the list of
sites, and many of this scripts subscribers to the autoresponder,
store data on the server. as well where in the sequence of
However, poorly designed scripts messages, each subscriber is.
can experience performance Examples of autoresponder
problems and sometimes even data scripts:
corruption on busy (and not so http://www.scriptcavern.com/scr_e
busy) web sites. mail_auto.php
If you're not a programmer, why 2. Classified ad scripts store
should this matter to you? (at least) a list of all the
classified ads placed by
Answer: Even if you're just visitors. Examples of this type
installing and using server-side of script:
scripts, you'll want to make sure http://www.scriptcavern.com/scr_c
that the scripts that you choose lassified.php
don't randomly break or corrupt
your data. 3. Free for all links scripts
store a list of all links posted
First, some examples of the types by visitors. See some example
of scripts which store data on scripts listed at:
web servers include: http://www.scriptcavern.com/scr_f
fa.php
(Of course, many scripts in each
of these (and other) categories 4. Top site scripts usually store
are well-designed, and run a list of the members of the top
perfectly well even on very busy site as well as information about
web sites). the number of "votes" that each
has received. For examples of and does an update before the
this type of script, see first copy of the script has
http://www.scriptcavern.com/scr_t finished, a second copy of the
opsite.php script starts running at the same
time.
So what kind of scripts have
problems? And what sort of 3. There are a number of ways
problems am I talking about? things can now go wrong, for
example:
Well the principle problems all
relate to what happens when bits (a) What if the first copy of the
of data from multiple users needs script reads in the data, then
to be stored on updated at the the second copy reads the same
same time. Some scripts handle data, then the first copy updates
these situations well, but others the data, then the second copy
don't... updates the data? Answer: any
changes made by the first copy of
DATA CORRUPTION the script can get lost.
Here's a common data corruption (b) What if the first and second
problem that can occur with many copy of scripts are both adding
scripts: multiple bits of new data to the
store at the same time? For
1. When some bit of data needs to example, imagine each needs to
be updated, a copy of the store the headline, description
server-side script starts and the name of the person
running, and then starts updating posting a classified ad. Well,
it. what can happen (with some
scripts) is the two classified
2. If another user comes along ads can get intermingled, so you
might get (for example) solution by itself (in
HEADLINE-1, DESCRIPTION-1, particular, a script which just
HEADLINE-2, PERSON-1, does this could still have
DESCRIPTION-2, PERSON-2. Or worse problems if multiple copies of a
yet, you might get bits of each script update the same file at
part of each classified ad, mixed the same time), but it does make
with the bits of the other. This data corruption less likely, and
type of thing is usually really if corruption does occur, at
bad news, as your data may least it won't corrupt the entire
consequently becoming unusable data store in one go.
from that point on.
2. They can use file-locking.
Does this sound too unlikely a This means that if one copy of a
problem to worry about? Don't script is working with a file,
bank on it... even if it happens another copy of the script is
only 1 time in 1,000, or 1 in prevented from working on that
10,000, eventually it will file, until the first copy has
happen: You need a solution. finished. File-locking works if
done correctly, but programming
So the real question is: is it it into a script needs to be done
possible for programmers to very carefully and precisely, for
create scripts without these every single possible case...
kinds of problems? Fortunately even a tiny bug or omission can
the answer is yes, and there are allow the possibility of
a number of ways that programmers data-corruption in through the
can address it: backdoor!
1. They can store each bit of 3. They can use a database (such
data in a separate file. This as MySQL) to store the data.
isn't necessarily a total Provided the data is properly
structured in the database, the (or all the links on your top
database handles the locking site, or all the subscribers to
automatically. And, as the your autoresponder, etc.).
programmer doesn't have to write
their own special locking What would happen?
routines, the possibility of bugs
and omissions are much reduced. Answer: Because each update can
only be performed after the
PERFORMANCE PROBLEMS previous update has been
completely finished, your site
Of course, avoiding having your may be slow, or even unable to
data corrupted should be the handle all your users' requests.
paramount consideration in
choosing a script, but is there So what's the solution?
anything else we need to be
concerned about? There's two options that
programmers can use:
Answer: Performance
1. They can use lots of small
Of course, all webmasters are files and file-lock each
aiming to build busy high traffic individually (for example, one
web sites... but will your per classified, one per top site
scripts be able to handle the listing, etc.). Of course, this
load? needs to be handled very
carefully...
Go back and re-read the paragraph
on file-locking. Now think about 2. They can use a database (like
what would happen if all the MySQL), as databases allow any
classified ads on your classified one individual record ("row") to
page were stored in a single file be updated, even when another is
also being updated.
And one additional point:
IN CONCLUSION
3. Even the best script is not
Now, let's summarise: immune to hard-disk hardware
failures, your web host being
1. Scripts that store data in struck by lightning, and all the
files need to use file-locking to other snafus that can happen. So,
avoid data-corruption, and they do take regular back-ups of any
also need to break the data into data that you can't afford to
separately updateable chunks to lose!
avoid performance problems on
busy web sites. In short, even if you're not a
script programmer, you need to be
2. Scripts that store data in aware of data storage issues. In
databases (like MySQL), provided future, when considering a script
of course that they have been for your web site, don't be
properly coded, are usually less afraid to ask some hard questions
likely to suffer from about how it stores data and how
data-corruption or performance well it handles multiple users.
problems.
About the Author:
This article was written by Sunil Tanna of Answers 2000. For a
directory of ASP, CGI, PHP and Remotely hosted scripts, please
visit http://www.scriptcavern.com - and for scripts written by
Answers 2000 please visit http://www.scriptrocket.com
Read more articles by: Sunil Tanna
Article Source: www.iSnare.com
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