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).
Related
I am building an application that connects to a mysql database. I set up the data connections and data source (data set) and have begun working on development, going back and forth between adding tables and views to the database and adding forms and components to the application.
I have up to now used the "Configure Data Source with Wizard" wizard to refresh the dataset in the application. Sometimes it takes a couple click throughs to get it to fully load the changes, but that's not the end of the world.
Today, without me knowingly changing anything, when I click on the wizard button, the frame of the wizard opens and closes instantly.
My data is accessible, and the parts of the application already developed work just fine, but I don't know how to add new tables and views to my project. My worry is that something went screwy in one of the auto generated dbDataSet.* files.
I'm happy to provide more information if that will help.
To answer my own question for whomever comes here next:
I came across this solution:
https://stackoverflow.com/a/4749044/7640114
It links to a microsoft.com page that is no longer available, but copies the relevant information. Finding the corresponding files is not hard, but knowing what the wrong Provider is may not be so simple.
Mostly because of a lack of patience, I just went with the second option and deleted the entire folder, which may have been overkill. It worked, and I have access to the wizard again and can continue development, but it also wiped out my workspace layout which I now have to rebuild from my memory.
Win some/loose some. In the end, I suggest being more delicate and removing lines of code from DefaultView.SEView first, and then moving on to trying to delete the file and the folder if nessasary.
A while back I asked this question about splitting an MS Access application, and possibly leaving some of the non-table functionality in the BE. Well, I'm at it again... :)
Some of my tables will be such that they are never updated by the user. The data feed to these tables will be a fairly intensive code process, run daily, that extracts from Oracle, majorly massages the data & then writes to my tables (very different structure from Oracle).. There's no practical way to make it a live link to Oracle. All of the code for this will be in Modules/Class Modules, none in Forms. It absolutely would need to be changed if the schema of either the Access file or the Oracle server changes.
Given the foregoing, FE or BE?
I would put the code modules in a FE so that you can re-link a copy of the FE to a testing/development BE as the need arises. The code FE needn't be the same application FE you distribute to your users.
I don't know that I'm understanding your description -- from what I get it sounds like a temp table, i.e., with data that is replaced with something else on a regular basis. In that case, you certainly don't want it either in your front end or in your back end (if the back end is a Jet/ACE database). If that's what you have here, this data belongs in a separate back end.
For managing links to multiple back ends, you might find my Reconnect Utility useful. Since all of my apps have a temp database that's part of the front end, all of them need the ability to easy reconnect to more than one back end (the linked table manager is a real pain for that). Some of my apps have as many as four different target databases that the linked tables point at, and it's much easier to do that with my utility. It only works with Jet/ACE back ends, though (I've sketched out handling of other data sources, but never finished it, because I never needed it in any of my own applications!).
David Fenton recently mentioned in another thread that
"The only proper place for any Access app (since Windows 2000, in fact) is the folder the %AppData% environment variable points to."
I greatly respect David's knowledge, especially in all matters relating to Access, but I'm confused by this statement.
What is the advantage of following this advice, especially in an environment where you are going to have multiple people using the same computer to access your app?
Won't installing to this folder only install the app for one user? And if this is true, won't installing your app multiple times leave multiple, separate copies of your app on the machine? Hard drive space is cheap these days, but I still don't want a front end file and other supporting files (graphics, Word and Excel templates, etc.) copied multiple times onto a machine when one copy will do.
What are your thoughts? Am I missing something key to understanding David's advice?
Yes, this is an issue but the only way around it is, assuming the IT admins allow it, to create a folder in the root of C drive and install the Access FE database file in that folder. That said I'd stil use the Application Data folder even if files are duplicated. As you state hard drives are cheap.
This assumes you don't mean a Terminal Server/Citrix system where users are simultaneously logged into the system.
First off, this is an issue only for a workstation that has multiple users logging on to it. That's pretty uncommon, isn't it?
Second, you admit there's no issue with disk space, so the only real issue is keeping the front end up-to-date, and that issue is really completely orthogonal to the question of where the front end is being stored.
That issue can be addressed by using any of a number of solutions that automatically copy a new version of the front end when the user opens it (if needed). Tony Toews's Auto FE Updater is the best solution I know of. It's quite versatile and easy to use, and Tony's constantly improving it.
So, in short, I don't think there's any issue here at all.
If everything is always the same for every user on a given machine, then multiple copies of a file may not be such a good idea. But when that one exception occurs, you've painted yourself into a corner. They may need a different template version for example.
You seem to be in a rare situation for an Access developer.
You're running into a bit of an issue here, because you're thinking about the environment variable name %appdata%. That variable stores the directory returned by SHGetSpecialFolderPath(CSIDL_APPDATA).
What you're looking for is the directory returned by SHGetSpecialFolderPath(CSIDL_COMMON_APPDATA). There's no environment variable for that directory. This directory is (as the name indicates) common to all users.
The advantage of David's method is that the Access data is protected by NTFS access rights, when it's in CSIDL_APPDATA. A user can only delete his copy. In CSIDL_COMMON_APPDATA, anyone can delete the single shared copy.
It's probably always best to put these advice and tips into perspective. The assumption being made here is if your application is going to be utilized in a multi user mode (that means more than one user in the application of the same time), then it's pretty much assumed that your applications going to be split into two parts. The so called application part (front end), and then the data file only part, or so called backend part.
So, you have a FE and a BE.
In this environment, each individual user within your office will have their own copy of the application placed on their workstation. The BE (data file) is thus assumed to be placed on some share folder on a server.
In the case we're not going to have multiple users running this application, or the application is not really under development, then you really don't need to split your application into two parts. However if you split your application, it means all of your users can safely work and utilize your application while you work on a copy of the next great version of this application release. Without a split environment, you really can't have any workable development cycle.
It is a long time and honored suggestion that if you're going to use access in a multi user environments, each individual user must have a copy of the front end application placed on each individual computer. If you avoid this suggestion, the end result is instability in the general operation of your application.
I have an article here that explains on a conceptual level and doesn't just tell you two split your application, but explains well why you should split your application:
http://www.members.shaw.ca/AlbertKallal/Articles/split/index.htm
Currently I'm working with an in house white label cms that we resell to multiple clients and it all runs from the same box/db.
I'm just looking at converting this to have an ecommerce version that we'll run alongside it.
I'm wondering whether there will be an issue keeping all the products/categories/orders in one db or whether it would be advisory to separate each instance of the site into its own db for this.
These white label instances will only be sold to smaller companies that probably wont have masses of traffic/products and are looking for a simple ecommerce site. Anything larger will definitely get its own hosting and db.
But for smaller scale stuff do you think a single db will be ok?
#Tim: Aye I agree completely, however as I'm working from an existing codebase all of the site specific filtering code is built in. All I need to do is add a couple of fields to each table and the backend will already take care of all that filter for me.
Also the codebase I'm working from is set up with multiple access levels, user(public), userAdmin(customer) and admin(me), and is built in suck a way that I can generate a new site from the admin portal. I then just need to upload new templates/css/js/images and the whole new site is created.
So theoretically it may be more work to have to separate out the ecommerce databases than it would be to leave it in one.
Hence the question, if there is likely to be issues with having multiple sites in one DB I'll split it out, but if it's not going to make too much odds I'll leave it as is...
In fact I think I just answered my own question, I'll implement it into the existing codebase and set it up to run on one db, with the knowledge that i can always install the whole codebase on another box and run a single site on it if I need to :)
Thanks for the quick reply
Having everything piled into a single DB is going to complicate your code considerably. Instead of it being a configuration difference (which DB to connect to), you're going to be peppering your code with filters based on the current customer. I would vote for separate DBs in a heartbeat. Even if you wind up with excessive load from all the small DBs, it should be easy to add a new DB server and point new sites to the DB on the new server.
I can't see the complications this would create in your code being worth it in the long run.
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).