Post by JohnHi
I have an access 97 frontend/backend app. I need to upgrade backend to sql
server with necessary coding changes to then frontend. I have two questions;
1. Am I better off converting the app to a more recent version of Access
before upgrading backend to sql server?
The above is not a large requirement. It really depends much on the hardware
and the machines you have. Remember, each new version of a product takes
more memory and uses up more resources. So, if you not using the new
features
then you suffer a slow down. I am not aware that the "connection" to sql
server is going to be any better then the a97 version you are using.
What is improved in later versions of access is the up-sizing tools that
allow you to
upsize that back end data to sql server. Each version since 97 has improved
a bit in this area. On the other hand, you can use the sql server tools to
import that back end file, so it not that you have to use the up-sizing
wizard in ms-access to move up the data. You can certainly give the upsizing
wizard in a97 a try. I not used the a97 one (can't even recall if there is
one).
Keep in mind that after upgrading your back end to sql server you should
find
that about 99% of your vba code and everything else should work as before.
(you front end simply now has linked tables to sql server in place of links
to that back end.
Post by John2. Are their any documentations/pointers that I can use to guide me
through upgrading from Access to sql server process?
there is almost "too" much material in this regards...here is a few links
http://support.microsoft.com/default.aspx?scid=kb;en-us;175619&Product=acc
ACC2000: "Access 2000 Upsizing Tools" White Paper Available in Download
Center
http://support.microsoft.com/?id=241743
ACC2002: "Access 2002 Upsizing Tools" White Paper Available in Download
Center
http://support.microsoft.com/?id=294407
ACC2000: Optimizing for Client/Server Performance (odbc)
http://support.microsoft.com/?id=208858
ACC: "Upsizing to Microsoft SQL Server" White Paper Available in Download
Center (a95, and a97)
http://support.microsoft.com/?id=175619
HOW TO: Convert an Access Database to SQL Server (a97,a2000)
http://support.microsoft.com/?id=237980
ACC: Tips for Optimizing Queries on Attached SQL Tables
http://support.microsoft.com/?id=99321
====
I add my tips here:
SQL server is indeed a high performance system, and also a system that can
scale to many many users.
If you write your application in c++, or VB or in your case with ms-access,
in GENERAL the performance of all of these tools will BE THE SAME.
In other words...sql server is rather nice, and is a standard system used in
the IT industry.
However, before you convert..how well does your application run now?
We often see posts here that a application is too slow with one user. If the
application is too slow with one user..then what can one expect when they
try and run 10 users. That is now 10 times the requirements..
The other issue is how well is the database setup?
Further..how well are the forms designed?
How well does the application work with 5 users..and then when you jump to
10 users...how much a slow down to you notice?
A few things:
Having a table with 75k records is quite small. Lets assume you have 12
users. With a just a 100% file base system (jet), and no sql server, then
the performance of that system should really have screamed.
Before Microsoft started "really" selling sql server, they rated JET could
handle easily 50 users. We have credible reports here of people
running 100 users. however, in those cases everything must be
"perfect".
I have some applications out there with 50, or 60 HIGHLY related tables.
With 5 to 10 users on a network, response time is instant. I don't think any
form load takes more then one second. Many of those 60+ tables are highly
relational..and in the 50 to 75k records range.
So, with my 5 users..I see no reason why I cant scale to 15 users with
such small tables in the 75,000 record range.
If the application did not perform with such small tables of only 75k
records..then upsizing to sql server will do absolute nothing to fix
performance issues. In fact, in the sql server newsgroups you see weekly
posts by people who find that upgrading to sql actually slowed things down.
I even seem some very cool numbers showing that some queries where actually
MORE EFFICIENT in terms of network use by JET then sql server.
So, keep in mind that moving to sql sever will likely result is LESS
performance then what you have now *unless* your designs limit records
transferred to the front end.
My point here is that technology will NOT solve performance problems.
However, good designs that make careful use of limited bandwidth resources
is the key here. So, if the application was not written with good
performance in mind..then you kind are stuck with a poor design!
I mean, when using a JET file share, you grab a invoice from the 75k record
table..only the one record is transferred down the network with a file share
(and, sql server will also only transfer one record). So, at this point, you
really will NOT notice any performance difference by upgrading to sql
server. There is no magic here.
Sql server is a robust and more scalable product then is JET. And, security,
backup and host of other reasons make sql server a good choice.
However, sql server will NOT solve a performance problem with dealing
with such small tables as 75k records
Of course, when efforts are made to utilize sql server, then
significant advances in performance can be realized.
I will give a few tips...these apply when using ms-access as a file
share (without a server), or even odbc to sql server:
** Ask the user what they need before you load a form!
The above is so simple, but so often I see the above concept ignored.
For example, when you walk up to a instant teller machine, does it
download every account number and THEN ASK YOU what you want to do? In
access, it is downright silly to open up form attached to a table WITHOUT
FIRST asking the user what they want! So, if it is a customer invoice, get
the invoice number, and then load up the form with the ONE record (how can
one record be slow!). When done editing the record...the form is closed, and
you are back to the prompt ready to do battle with the next customer. You
can read up on how this "flow" of a good user interface works here (and this
applies to both JET, or sql server applications):
http://www.members.shaw.ca/AlbertKallal/Search/index.html
My only point here is restrict the form to only the ONE record the user
needs. Of course, sub-forms, and details records don't apply to this rule,
but I am always dismayed how often a developer builds a nice form, attaches
it to a large table, and then opens it..and the throws this form attached to
some huge table..and then tells the users to go have at and have fun. Don't
we have any kind of concern for those poor users? Often, the user will not
even know how to search for something ! (so, prompt, and asking the user
also makes a HUGE leap forward in usability. And, the big bonus is reduced
network traffic too!...Gosh...better and faster, and less network
traffic....what more do we want!).
** Don't use quires that require more then one linked table
(this ONLY applies to odbc to sql server...you CAN and are FREE to do this
with a mdb JET file share..and also with ADP projects to sql server).
When you use
ODBC, one table could be on the corporate server, and the other ODBC might
be a FoxPro table link 3 computers from the left of you. As a result..JET
has a real difficult time joining these tables together..and JET can not
assume that the two tables are on the same box..and thus have the "box" join
the tables. Thus,while jet does it best..these types of joins can often be
real slow. (note the word "often" here, it not "always" the case. So, if
existing quires run ok speed wise, then don't waste time fixing them.
In a migration to sql server, simply moving up the data back end and
linking should get your application almost working. it is "then" you
start to address parts that simply run too slow.
The simple solution in these slow query cases is to change the query to
a view and link to that. This is the least amount of work, and means the
joins occur on the server side. This also applies to combo boxes. Most
combos boxes has sql embedded in them. That sql has to be processed, and
then thrown to a linked odbc table. This is a bit sluggish. (a form can have
maybe one, or two combos..but after that ..it will start to load slow). So,
remove the sql from the combo box, build a view..and link the combo box
direct to that view (JUST USE the view name...the sort, and any sql need to
be in the view). The result is quite good combo box load performance. (and
again, not very much work. There are other approaches that can even speed
this up more..but we have to balanced the benefits VS. the amount of work
and coding. I don't think once should re-code all combo boxes to a call back
with a pass-through reocrdset..but that can be a solution also).
If you are using a ADP access project, the above points about the joins
with more then one table does NOT apply..since all queries execute
on the sql server side. (perhaps you could consider converting the
application to a ADP project. It would at least force you to make
most sql run on the server side. However, ODBC is just fine
and is usually EQUAL in performance if you do things right).
** Of course, if you do have sql with more then one table..then pass-though
is the best if using odbc. (again..this does NOT apply to a mdb JET file
share).
** You can continue to use bound forms..but as mentioned..restrict the form
to the one record you need. You can safely open up to a single invoice,a and
even continue to use the "where" clause of the openform. Bound forms are way
less work then un-bound forms...and performance is generally just is good
anyway when done right.
** Large loading of combo boxes. A combo box is good for about 100
entries. After that..you are torturing the user (what..they got to look
through 100s of entries). So, keep things like combo boxes down
to a min size. This is both faster..and MORE importantly it is
kinder to your users.
After all, at the end of the day..what we really want is to make
things easy for the users...and treat them well.. It seems that
treating the users well, and reducing the bandwidth
(amount of data) goes hand in hand. So, better applications
treat the users well..and run faster! (this is good news!)
--
Albert D. Kallal (Access MVP)
Edmonton, Alberta Canada
***@msn.com