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I've been researching this question over the last few days as I prepare to deliver the first of 3 phases with my first system using a split database. I would like your advice as I haven't found enough info to make a full decision yet.
At the moment I'm working in dev on an unsplit database. When I split it in live I'll take a copy of both parts but what do I do with them for phase 2?
I'm thinking that I'll now make them my dev version after relinking the tables (as I've effectively moved the back end) which would then mean that I no longer work with the unsplit database. Is that the right approach?
When it comes to putting phase 2 live I don't think I have any choice other than manually applying table updates to the live back end (once backed up). For the live front end, do I just replace it with my dev front end and then relink the tables or do I export the changes into the live front end? I guess I could do either depending on the number of objects that are changing/new. Is that right? I'll then take copies and make them my dev versions for phase 3.
Finally in dev I have form and report templates and test forms, reports and queries which are not needed in live so do I remove them for each deployment and then add them all back in to the new dev front end or just put them live? Normally I would take them out but there are a lot of them and I don't know of any quick way to add them back in so what do you do?
Primarily my questions are asked from a risk point of view - what steps best reduce the risk of messing things up in live.
Update:
For those of you who are looking for answers on this, in addition to the fine responses below I have since found the following that might also help:
How to Continuously Develop and Deploy an Access 2010 Database Application
At the moment I'm working in dev on an unsplit database. W
Don't, a VERY bad idea. How this works?
Well, for sure at the start, you are building LOTS of new tables, changing relationships, and building tables at a high rate of development.
so, at this point in time, you can develop un-split.
You will then find after some time the rate (and need) to create new tables, and change the so called "database schema" calms down to a dull roar.
At this point your still developing away - not yet deployed.
So, somewhere around this point? You want to split. You REALLY want to do this.
There is a boatload of reasons for this, but several are:
while a split vs non split is "very similar", they are not the same!
Thus, you can't and don't want to develop code that NOT really tested
as to HOW the code will run in the real world
So, many issues can change or crop up during development that is DIFFERENT when run split. So some commands (such as seek()) don't work, and a few other issues can crop up. You don't want to develop for a whole week, then split and now find 20 hard to fix bugs in your code. So, by developing as split as soon as possible, then ANY and ALL issues that come up will be seen as you develop along, and thus can fix, see, and deal with such issues at THAT POINT in time. Much worse is to write a bunch of code, get ready to deploy, and then find new bugs.
Next up:
Having a split system is great, since say a customer might let you remote into their system. You can pull down a copy of their data, re-link your tables to point from your "test data" to real live production data.
Or, say your developing on site. You might want to test some dangerous delete code, or code that modifies the data. So, you can't risk working on production data, so now you re-link and point to your test back end. So, this setup allows you to test code, but MORE important test on a copy of the database with great ease.
And it also allows you to develop off site. You can take the latest front end for their system, maybe get their latest data file, maybe not. but you can now with ease simple change the database that your applcation runs with.
The other big issue? Say your working on site, and have a test database of theirs on the network folder. You write some code, test for a new report. You find it runs SLOW AS A TURTLE. You check your code, maybe add a few indexes, and boom! - your report now runs great.
If you test un-split, then a boatload of performance issues can crop up, but NOT SEEN during the development cycle. Once again, you don't want to develop for weeks or whatever, split, and NOW find a whole bunch of forms and code runs REALLY slow.
So, the goal, the idea here?
You want to get split as SOON as possible?
How soon?
Well, this is one of those things that only you can know!!!
As I stated, at start of development, sure, start out un-split.
Once the table designs are quite solid, then you can split. You then ALWAYS develop as split (and the above list of reasons why is the VERY short list - there are many more reasons).
Now, the problem of course with split? Say you want to add a new column to a table?
Well, it is MORE work, since now ANY AND ALL changes to the data schema are done in the back end. So, you have to close down the front end (FE), open the back end, and now use the table designer to add that one column. (or maybe change or setup a new relationship between some tables. Or maybe add a new table).
This is a "bit more" work, since now you close down the BE, and open the FE, and now you MUST re-link tables. And if you added new tables to the BE, then you have to add that/those new table links.
Because this "dance" is extra work, that is why you wait as long as possible to split. As I stated, you "just know" when that time has arrived to split. (when table and schema tables changes settles down to a low rate of change). Since the rate of change is now low in regards to table changes, then it not much work nor pain to have to do the above every time you want to change the table structures.
In fact, think of any program you buy? It has a applcation part, and then a data file part. In effect, once you split, you have the same two parts, and in fact in some applications I written, they are allowed to use "different" back ends - not unlike any other applcation in which you launch the applcation, and THEN choose the datafile to work with.
So, what about developing off site? Well, that can be REALLY difficult, since you have your own copy of the FE and the BE.
If you HAVE TO make changes to the BE?
I open up a work document. And if I add a new column to say tblCusotmers?
Then I enter this:
Add new column TaxRate, Currency, to table tblCustomers
So, you build up a "log" of changes. Now, when you travel to the customer site, and want to roll out and deploy the new FE? Well, you have to FIRST open up their BE, and make the above changes to their production BE database.
Now in some cases, where is was not possible for me to be on site? (in fact, I had a automatic update system to automatic roll out a new version of my software - and it would automatic down load from the internet. In this case? I had to write code in the FE on startup that would use VBA code to MAKE the changes to the data tables. This can be REALLY hard to do, but is possible. I just recommend the plane jane word document, and you keep track of your changes.
So, the above is quite much how this development process works.
Since you will have to re-link the tables? Then near everyone has googled for a VBA table re-link routines. You want that, since having such code is MUCH easier then say using the linked table manager each time. And we even often have a table in the FE that saves the BE server location, and on startup will check, and if the location of the files don't match, we launch the re-link code.
that way, you can deploy the applcation to different sites, and have it automatic re-link. Another way is to have a simple text file in the same location as the FE on each computer, and on startup read the text file with the BE location - and re-link if required.
So, the typical process to role out a new FE (which is placed on each work station - do NOT break this rule!!!).
So, I point/relink my front end to the production BE. I then compile down to a accDE, and then deploy that new compiled FE to all the work stations. In fact, I have some code in VBA at start up that compares a version number, and if the version number is lower, then the VBA code will copy down the next FE sitting in a folder.
This might not be a big deal if you have 2-4 users. But, if you have two sites, and each has 35 users, then you want to figure out a automated approach.
However, do not prolong jumping over to the split development cycle, as you really for all practical purposes MUST develop in a split environment. So, for the first part, you can develop un-split. But, once you split - that's it, and from that point on-wards, you are to develop as split. There are boatloads of benefits, but it also really quite much standard approach from a developer point of view.
So, you have to master the linked table manager rite quick, and then VERY much consider adding some re-link code, since you want with great ease to point to a different back end - including at deployment time.
so, as a general rule, you should think of your FE like a .exe program, for a new version roll out, yes, you copy (over write) their existing FE's on each work station. And as noted, in most cases, it should be a compiled accDE, and not a un-compiled accDB for the FE.
For reducing risk:
you should have your development version, a test version for live and the live version.
You are developing on develop
Customer tests the changes on test (with test data)
after that you move to live
For the move from develop to test I create an update/migration script.
In this script are all alterations included that needs to be done on the back-end.
I use the script to create the test version and with this I can check if it is working properly.
In case there are database changes that I can't reflect in my script (either insufficient skill or restrictions from db) I add them to my checklist.
I am using version control to see changes during development and to import modules, queries etc. to the new version.
Updating the front end is done via Import of the latest version (without not needed forms / reports).
In our company, we created a small Access database, which was in a network folder for everyone to access it.
After a while we decided to split it into a backend and a frontend. The new frontend is at the same location the original data was while the original data, serving as the backend now, is in a subfolder of the folder it used to be located in, so all relevant data is accessible to the the employees as it has always been.
The current problem is, that today, most of the time both the BE and the FE have their ".Iaccdb" files showing up and if you try to open any of the two, BE or FE, it will say, that a user is using the database in the exclusive mode.
I guess solving the problem at hand isn't the main issue here. What I rather like to know is, WHAT must have happened, to cause both files to behave this way.
I heard about this happening to either the BE or the FE, but never both simultaneously.
Never use a shared frontend:
Deploy and update a Microsoft Access application with one click.
I found out what caused the issue and in doing so also have to apologize for omiting one relevant detail: The old file I started with also had connections to Sharepoint lists.
Because of that, I couldnt just use the split function as it doesn't work if you're database is connected to Sharepoint.
So my workaround was to copy the access file in the upper folder as the new FrontEnd. In this new file/FE, i just created links to the old file's table, which now serves as the backEnd.
As I said, there were connections in the old file/BE.
When I first tried the FE, it worked properly. only when someone already opened the FE and another one wanted to do the same, the issue of users blocking each other appeared.
My solution was to get rid of the SharePoint connections in the old file/BE and now everything works smoothly.
I split my DB and now when I try to change some information on a few queries, I can't access them. I have a front end and a back end and understand that I should make changes to queries/forms via the front end, but they are grayed out and inaccessible.
At this point, I tried unsplitting the DB (which I believe I did), but I still can't edit those queries or forms.
I can click on the query/form and see the result of it, but I can't get to design view to edit it.
I'm taking a shot in the dark and saying that in the process of splitting your database, you either created your front-end in an accdr or accde format (a runtime application). The purpose of this is that you shouldn't be able to open queries or forms or tables in design view on the front end. You can just open your database and save it again as an accdb file and continue as normal.
If you're having other problems with the linked tables, I suggest you open the Linked Table Manager and refresh the links (if you moved the backend file, this is necessary).
I would recommend trying to proceed as normal by using Shift Bypass just to be sure. ( Hold the shift key when you start the database. Then attempt to modify in design view).
If these fail, I would attempt to copy the queries and /or forms if possible and create new ones.
I have a front-end Access 2007 apllication which talks to MySql server.
I want to have a feature where the application on the user's computer can detect that there is a new version on the network (which is not difficult) and download the latest version to the local drive and launch it.
Does anybody has any knowledge or exprience how this can be done?
Thanks
Do you actually need to find out if there is a newer version?
We have a similar setup as well, and we just copy the frontend and all related files every time someone starts the application.
Our users don't start Access or the frontend itself. They actually start a batch file which looks something like this:
#echo off
xcopy x:\soft\frontend.mde c:\app\ /Y
c:\app\frontend.mde
When we started writing our app, we thought about auto-updating as well and decided that just copying everything everytime is enough.
We have enough bandwidth, so the copying doesn't create any performance problems (with about 200 users).
Plus, it makes some things easier for me as a developer when I can be sure that each time the application is started, the frontend is overwritten anyway.
I don't have to care about auto-compacting the frontend when it's closed (and users complaining that closing the app takes too long...), and I don't have to deal with corrupted frontends after crashes.
#Lumis - concerning the custom icon:
Ok, maybe I should have made this more clear. There is only one batch file, and it's in the same network folder as the frontend.
The users just have links on their desktops which all point to the same batch file in the network folder.
This means that:
future changes to the batch file are easy, because it's only one single
file in one central place
we can change the icon, because
what the user sees is a normal Windows link
(By the way, we did not change the icon. Our app is for internal use only, and I'm working in a manufacturing company, which means that all but very few users are absolutely non-technical and couldn't care less about the icon, as long as it's the same on all machines and they know how it looks like so they can find it quickly on their desktop...)
Tony Toews has one: Access Auto FE Updater
It appears to be free, but I'm not 100% sure.
Lumis's option is solid, however if you want to check the version and only copy the database when their is a new version, have a 'Version' field in a back end table, and a 'Version' constant in a front end module. Keep these in sync with each new production release. Compare the table version against the version in the module when the main form of the front end database opens.
If they don't match, have the database close, but have the database call a batch file as the last bit of code to run as it's closing. The database should finish closing before the batch file begins it's copy process. If needed, place a minor delay in the batch file code just to be sure there are no file locking issues.
I have created an MS Access 2003 application, set up as a split front-end/back-end configuration, with a user group of about five people. The front end .mdb sits on a network file server, and it contains all the queries, forms, reports, and VBA code, plus links to all the tables in the back end .mdb and some links to ODBC data sources like an AS/400. The back end sits on the same network file server, and it just has the table data in it.
This was working well until I "went live" and my handful of users started coming up with enhancement requests, bug reports, etc. I have been rolling out new code by developing/testing in my own copy of the front-end .mdb in another network folder (which is linked to the same back-end .mdb), then posting my completed file in a "come-and-get-it" folder, alerting the users, and they go copy/paste the new front-end file to their own folders on the network. This way, each user can update their front end when they're at a 'stopping point' without having to boot everyone out at once.
I've found that when I'm developing now, sometimes Access becomes extremely slow. Like, when I am developing a form and attempt to click a drop-down on the properties box, the drop-down arrow will push in, but it will take a few seconds before the list of options appears. Or there's tons of lag in selecting & moving controls on a form. Or lots of keyboard lag.
Then, at other times, there's no lag at all.
I'm wondering if it's because I'm linked to the same back end as the other users. I did make a reasonable effort to set up the queries, forms, reports etc. with minimal record locking, if any at all, depending on the need. But I may have missed something, or perhaps there is some other performance issue I need to address.
But I'm wondering if there is an even better way for me to set up my own development back-end .mdb, so I can be testing my code on "safe" data instead of the same live data as the rest of the users. I'm afraid that it's only a matter of time before I corrupt some data, probably at the worst possible moment.
Obviously, I could just set up a separate back-end .mdb and manually reconfigure the table links in the front end every time, using the Linked Table Manager. But I'm hoping there is a more elegant solution than that.
And I'm wondering if there are any other performance issues I should be considering in this multi-user, split database configuration.
EDIT: I should have added that I'm stuck with MS Access (not MS-SQL or any other "real" back end); for more details see my comment to this post.
If all your users are sharing the front end, that's THE WRONG CONFIGURATION.
Each user should have an individual copy of the front end. Sharing a front end is guaranteed to lead to frequent corruption of the shared front end, as well as odd corruptions of forms and modules in the front end.
It's not clear to me how you could be developing in the same copy of the front end that the end users are using, since starting with A2000, that is prohibited (because of the "monolithic save model," where the entire VBA project is stored in a single BLOB field in a single record in one of the system tables).
I really don't think the problems are caused by using the production data (though it's likely not a good idea to develop against production data, as others have said). I think they are caused by poor coding practices and lack of maintainance of your front end code.
turn off COMPILE ON DEMAND in the VBE options.
make sure you require OPTION EXPLICIT.
compile your code frequently, after every few lines of code -- to make this easy, add the COMPILE button to your VBE toolbar (while I'm at it, I also add the CALL STACK button).
periodically make a backup of your front end and decompile and recompile the code. This is accomplished by launching Access with the /decompile switch, opening your front end, closing Access, opening your front end with Access (with the SHIFT key held down to bypass the startup code), then compacting the decompiled front end (with the SHIFT key held down), then compiling the whole project and compacting one last time. You should do this before any major code release.
A few other thoughts:
you don't say if it's a Windows server. Linux servers accessed over SAMBA have exhibited problems in the past (though some people swear by them and say they're vastly faster than Windows servers), and historically Novell servers have needed to have settings tweaked to enable Jet files to be reliably edited. There are also some settings (like OPLOCKS) that can be adjusted on a Windows server to make things work better.
store your Jet MDBs in shares with short paths. \Server\Data\MyProject\MyReallyLongFolderName\Access\Databases\ is going to be much slower reading data than \Server\Databases. This really makes a huge difference.
linked tables store metadata that can become outdated. There are two easy steps and one drastic one to be taken to fix it. First, compact the back end, and then compact the front end. That's the easy one. If that doesn't help, completely delete the links and recreate them from scratch.
you might also consider distributing an MDE to your end users instead of an MDB, as it cannot uncompile (which an MDB can).
see Tony Toews's Performance FAQ for other generalized performance information.
1) Relink Access tables from code
http://www.mvps.org/access/tables/tbl0009.htm
Once I'm ready to publish a new MDE to the users I relink the tables, make the MDE and copy the MDE to the server.
2) I specifically created the free Auto FE Updater utility so that I could make changes to the FE MDE as often as I wanted and be quite confident that the next time someone went to run the app that it would pull in the latest version. For more info on the errors or the Auto FE Updater utility see the free Auto FE Updater utility at http://www.granite.ab.ca/access/autofe.htm at my website to keep the FE on each PC up to date.
3) Now when working on site at a clients I make the updates to the table structure after hours when everyone is out of the system. See HOW TO: Detect User Idle Time or Inactivity in Access 2000 (Q210297) http://support.microsoft.com/?kbid=210297 ACC: How to Detect User Idle Time or Inactivity (Q128814) http://support.microsoft.com/?kbid=128814
However we found that the code which runs on the timer event must be disabled for the programmers. Otherwise weird things start happening when you're editing code.
Also print preview would sometimes not allow the users to run a menu item to export the report to Excel or others. So you had to right click on the Previewed report to get some type of internal focus back on the report so they could then export it. This was also helped by extending the timer to five minutes.
The downside to extending the timer to five minutes was if a person stays in the same form and at the same control for considerable parts of the day, ie someone doing the same inquiries, the routine didn't realize that they had actually done something. I'll be putting in some logic sometime to reset this timer whenever they do something in the program.
4) In reference to another person commenting about scripts and such to update the schema see Compare'Em http://home.gci.net/~mike-noel/CompareEM-LITE/CompareEM.htm. While it has its quirks it does create the VBA code to update tables, fields, indexes and relationships.
Use VBA to unlink and re-link your tables to the new target when switching from dev to prod. It's been to many years for me to remember the syntax--I just know the function was simple to write.
Or use MS-Access to talk to MS-Access through ODBC, or some other data connection that lives outside of the client mdb.
As with all file base databases, you will eventually run into problems with peak usage or when you go over a small magical number somewhere between 2 and 30.
Also, Access tends to corrupt frequently, so backup, compact and repair need to be done on an frequent basis. 3rd party tools used to exist to automate this task.
As far as performance goes, the data is being processed client side, so you might want to use something like netmeter to watch how much data is going over the wire. The same principle about indexing and avoiding table scans apply to file base dbs as well.
Many good suggestions from other people. Here's my 2 millicents worth. My backend data is on server accessed through a Drive mapping. In my case, the Y drive. Production users get the mapping through a login script using active directory. Then the following scenarios are easily done by batch file:
Develop against local computer by doing a subst command in a batch file
run reports against last nights data by pointing Y to the backup server (read only)
run reports against end of month data by pointing to the right directory
test against specialized scenarios by keeping a special directory
In my environment (average 5 simultaneous users, 1000's of rows, not 10,000's.) corruption has occurred, but it's rare and manageable. Only once in the last several years have we resorted to the previous days backup. We use SQL Server for our higher volume stuff, but it's not as convenient to develop against, probably because we don't have a SQL admin on site.
You might also find some of the answers to this question (how to extract schemas from access) to be useful as well. Once you've extracted a schema using one of the techniques that were suggested you gain a whole range of new options like the ability to use source control on the schemas, as well as being able to easily build "clean" testing environments.
Edit to respond to comment:
There's no easy way to source control an Access database in it's native format, but schema files are just text files like any other. Hence, you can check them in and out of the source control software of your choice for easy version control/rollbacks.
Or course, it relies on you having a series of scripts set up to re-build your database from the schema. Once you do, it's normally fairly trivial to create an option/alternative version that rebuilds it in a different location, allowing you to build test environments from any previous committed version of the schema. I hope that clarifies a bit!
If you want to update the back end MDB schema automatically when you release a new FE to the clients then see Compare'Em http://home.gci.net/~mike-noel/CompareEM-LITE/CompareEM.htm will happily generate the VBA code need to recreate an MDB. Or the code to create the differences between two MDBs so you can do a version upgrade of the already existing BE MDB. It's a bit quirky but works.
I use it all the time.
You need to understand that a shared mdb file for the data is not a robust solution. Microsoft would suggest that SQL Server or some other server based database would be a far better solution and would allow you to use the same access front end. The migration wizard would help you make the changeover if you wanted to go that way.
As another uses pointed out, corruption will occur. It is simply a question of how often, not if.
To understand the performance issues you need to understand that to the server the mdb file with the data in it is simply that, a file. Since no code runs on the server, the server does not understand transactions, record locking etc. It simply knows that there is a file that a bunch of people are trying to read and write simultaniously.
With a database system such as SQL Server, Oracle, DB2. MySQL etc. the database program runs on the server and looks to the server like a single program accessing the database file. It is the database program (running on the server) that handles record locking, transactions, concurrency, logging, data backup/recovery and all the other nice things one wants from a database.
Since a database program designed to run on the server is designed to do that and only that, it can do it far better and more efficently that a program like Access reading an writing a shared file (mdb).
There are two rules for developing against live data
The first rule is . . . never develop
against live data. Not ever.
The second rule is . . .never develop
against live data. Not ever.
You can programatically change the bindings for linked tables, so you can write a macro to change your links when you're deploying a new version.
The application is slow because it's MS Access, and it doesn't like many concurrent users (where many is any number > 1).