Setting up an MS-Access DB for multi-user access

Question

We re thinking of  growing  a little MS-Access DB with a few tables  forms and queries for multiple users   Using a different back-end is another  but more long-term option that is unfortunately currently not acceptable   Most users will be read-only  but there will be a few  currently one or two  users that have to be able to do changes  while the read-only users are also using the DB   We re not so much concerned about the security aspects  but more about some of the following issues    How can we make sure that the write-user can make changes to the table data while other users use the data  Do the read-users put locks on tables  Does the write-user have to put locks on the table  Does Access do this for us or do we have to explicitly code this  Are there any common problems with  MS Access transactions  that we should be aware of  Can we work on forms  queries etc  while they are being used  How can we  program  without being in the way of the users  Which settings in MS Access have an influence on how things are handled  Our background is mostly in Oracle  where is Access different in handling multiple users  Is there such thing as  isolation levels  in Access    Any tips or pointers to helpful articles would be greatly appreciated

User · Answer

i think Access is a best choice for your case. But you have to split database, see: http://accessblog.net/2005/07/how-to-split-database-into-be-and-fe.html

•How can we make sure that the write-user can make changes to the table data while other users use the data? Do the read-users put locks on tables? Does the write-user have to put locks on the table? Does Access do this for us or do we have to explicitly code this?

there are no read locks unless you put them explicitly. Just use "No Locks"

•Are there any common problems with "MS Access transactions" that we should be aware of?

should not be problems with 1-2 write users

•Can we work on forms, queries etc. while they are being used? How can we "program" without being in the way of the users?

if you split database - then no problem to work on FE design.

•Which settings in MS Access have an influence on how things are handled?

What do you mean?

•Our background is mostly in Oracle, where is Access different in handling multiple users? Is there such thing as "isolation levels" in Access?

no isolation levels in access. BTW, you can then later move data to oracle and keep access frontend, if you have lot of users and big database.

User · Answer

Access is a great multi-user database  It has lots of built in features to handle the multi-user situation  In fact  it is so very popular because it is such a great multi-user database  There is an upper limit on how many users can all use the database at the same time doing updates and edits - depending on how knowledgeable the developer is about access and how the database has been designed - anywhere from 20 users to approx 50 users  Some access databases can be built to handle up to 50 concurrent users  while many others can handle 20 or 25 concurrent users updating the database  These figures have been observed for databases that have been in use for several or more years and have been discussed many times on the access newsgroups

User · Answer

Table or record locking is available in Access during data writes. You can control the Default record locking through Tools | Options | Advanced tab:

No Locks
All Records
Edited Record

You can set this on a form's Record Locks or in your DAO/ADO code for specific needs.

Transactions shouldn't be a problem if you use them correctly.

Best practice: Separate your tables from All your other code. Give each user their own copy of the code file and then share the data file on a network server. Work on a 'test' copy of the code (and a link to a test data file) and then update user's individual code files separately. If you need to make data file changes (add tables, columns, etc), you will have to have all users get out of the application to make the changes.

See other answers for Oracle comparison.

User · Answer

I have found the SMB2 protocol introduced in Vista to lock the access databases. It can be disabled by the following regedit:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\LanmanServer\Parameters] "Smb2"=dword:00000000

User · Answer

I find the answers to this question to be problematic  confusing and incomplete  so I ll make an effort to do better   Q1  How can we make sure that the write-user can make changes to the table data while other users use the data  Do the read-users put locks on tables  Does the write-user have to put locks on the table  Does Access do this for us or do we have to explicitly code this   Nobody has really answered this in any complete fashion  The information on setting locks in the Access options has nothing to do with read vs  write locking  No Locks vs  All Records vs  Edited Record is how you set the default record locking for WRITES     No locks means you are using OPTIMISTIC locking  which means you allow multiple users to edit the record and then inform them after the fact if the record has changed since they launched their own edits  Optimistic locking is what you should start with as it requires no coding to implement it  and for small users populations it hardly ever causes a problem  All Records means that the whole table is locked any time an edit is launched  Edited Record means that fewer records are locked  but whether or not it s a single record or more than one record depends on whether your database is set up to use record-level locking  first added in Jet 4  or page-level locking  Frankly  I ve never thought it worth the trouble to set up record-level locking  as optimistic locking takes care of most of the problems    One might think that you want to use record-level pessimistic locking  but the fact is that in the vast majority of apps  two users are almost never editing the same record  Now  obviously  certain kinds of apps might be exceptions to that  but if I ran into such an app  I d likely try to engineer it away by redesigning the schema so that it would be very uncommon for two users to edit the same record  usually by going to some form of transactional editing instead  where changes are made by adding records  rather than editing the existing data    Now  for your actual question  there are a number of ways to accomplish restricting some users to read-only and granting others write privileges  Jet user-level security was intended for this purpose and works fine insofar as it s  security  for any meaningful definition of the term  In general  as long as you re using a Jet ACE data store  the best security you re going to get is that provided by Jet ULS  It s crackable  yes  but your users would be committing a firable offense by breaking it  so it might be sufficient   I would tend to not implement Jet ULS at all and instead just architect the data editing forms such that they checked the user s Windows logon and made the forms read-only or writable depending on which users are supposed to get which access  Whether or not you want to record group membership in a data table  or maintain Windows security groups for this purpose is up to you  You could also use a Jet workgroup file to deal with it  and provide a different system mdw file for the write users  The read-only users would log on transparently as admin  and those logged on as admin would be granted only read-only access  The write users would log on as some other username  transparently  in the shortcut you provide them for launching the app  supplying no password   and that would be used to set up the forms as read or write   If you use Jet ULS  it can become really hairy to get it right  It involves locking down all the tables as read-only  or maybe not even that  and then using RWOP queries to provide access to the data  I haven t done but one such app in my 14 years of professional Access development   To summarize my answers to the parts of your question   How can we make sure that the write-user can make changes to the table data while other users use the data   I would recommend doing this in the application  setting forms to read only or editable at runtime depending on the user logon  The easiest approach is to set your forms to be read-only and change to editable for the write users when they open the form   Do the read-users put locks on tables   Not in any meaningful sense  Jet ACE does have read locks  but they are there only for the purpose of maintaining state for individual views  and for refreshing data for the user  They do not lock out write operations of any kind  though the overhead of tracking them theoretically slows things down  It s not enough to worry about   Does the write-user have to put locks on the table   Access in combination with Jet ACE does this for you automatically  particularly if you choose optimistic locking as your default  The key point here is that Access apps are databound  so as soon as a form is loaded  the record has a read lock  and as soon as the record is edited  whether or not it is write-locked for other users is determined by whether you are using optimistic or pessimistic locking  Again  this is the kind of thing Access takes care of for you with its default behaviors in bound forms  You don t worry about any of it until the point at which you encounter problems   Does Access do this for us or do we have to explicitly code this   Basically  other than setting editability at runtime  according to who has write access   there is no coding necessary if you re using optimistic locking  With pessimistic locking  you don t have to code  but you will almost always need to  as you can t just leave the user stuck with the default behaviors and error messages   Q2  Are there any common problems with  MS Access transactions  that we should be aware of   Jet ACE has support for commit rollback transactions  but it s not clear to me if that s what you mean in this question  In general  I don t use transactions except for maintaining atomicity  e g   when creating an invoice  or doing any update that involves multiple tables  It works about the way you d expect it to but is not really necessary for the vast majority of operations in an Access application   Perhaps one of the issues here  particularly in light of the first question  is that you may not quite grasp that Access is designed for creating apps with data bound to the forms   Transactions  is a topic of great importance for unbound and stateless apps  e g   browser-based   but for data bound apps  the editing and saving all happens transparently    For certain kinds of operations this can be problematic  and occasionally it s appropriate to edit data in Access with unbound forms  But that s very seldom the case  in my experience  It s not that I don t use unbound forms -- I use lots of them for dialogs and the like -- it s just that my apps don t edit data tables with unbound forms  With almost no exceptions  all my apps edit data with bound forms    Now  unbound forms are actually fairly easy to implement in Access  particularly if you name your editing controls the same as the underlying fields   but going with unbound data editing forms is really missing the point of using Access  which is that the binding is all done for you  And the main drawback of going unbound is that you lose all the record-level form events  such as OnInsert  BeforeUpdate and so forth   Q3  Can we work on forms  queries etc  while they are being used  How can we  program  without being in the way of the users   This is one of the questions that s been well-addressed  All multi-user or replicated Access apps should be split  and most single-user apps should be  too  It s good design and also makes the apps more stable  as only the data tables end up being opened by more than one user at a time   Q4  Which settings in MS Access have an influence on how things are handled    Things   What things   Q5  Our background is mostly in Oracle  where is Access different in handling multiple users  Is there such thing as  isolation levels  in Access   I don t know anything specifically about Oracle  none of my clients could afford it even if they wanted to   but asking for a comparison of Access and Oracle betrays a fundamental misunderstanding somewhere along the line    Access is an application development tool    Oracle is an industrial strength database server   Apples and oranges   Now  of course  Access ships with a default database engine  originally called Jet and now revised and renamed ACE  but there are many levels at which Access the development platform can be entirely decoupled from Jet ACE  the default database engine    In this case  you ve chosen to use a Jet ACE back end  which will likely be just fine for small user populations  i e   under 25  Jet ACE can also be fine up to 50 or 100  particularly when only a few of the simultaneous users have write permission  While the 255-user limit in Jet ACE includes both read-only and write users  it s the number of write users that really controls how many simultaneous users you can support  and in your case  you ve got an app with mostly read-only users  so it oughtn t be terribly difficult to engineer a good app that has no problems with the back end   Basically  I think your Oracle background is likely leading you to misunderstand how to develop in Access  where the expected approach is to bind your forms to recordsources that are updated without any need to write code  Now  for efficiency s sake it s a good idea to bind your forms to subsets of records  rather than to whole tables  but even with an entire table in the recordsource behind a data editing form  Access is going to be fairly efficient in editing Jet ACE tables  the old myth about pulling the whole table across the wire is still out there  as long your data tables are efficiently indexed   Record locking is something you mostly shouldn t have any cause to worry about  and one of the reasons for that is because of bound editing  where the form knows what s going on in the back end at all times  well  at intervals about a second apart  the default refresh interval   That is  it s not like a web page where you retrieve a copy of the data and then post your edits back to the server in a transaction completely unconnected to the original data retrieval operation  In a bound environment like Access  the locking file on the back-end data file is always going to be keeping track of the fact that someone has the record open for editing  This prevents a user s edits from stomping on someone else s edits  because Access knows the state and informs the user  This all happens without any coding on the part of the developer and is one of the great advantages of the bound editing model  aside from not having to write code to post the edits    For all those who are experienced database programmers familiar with other platforms who are coming to Access for the first time  I strongly suggest using Access like an end user  Try out all the point and click features  Run the form and report wizards and check out the results that they produce  I can t vouch for all of them as demonstrating good practices  but they definitely demonstrate the default assumptions behind the way Access is intended to be used   If you find yourself writing a lot of code  then you re likely missing the point of Access

User · Answer

The first thing to do  if not already done  is to split your database into a front end  with all the forms reports etc  and a back end with all the data   The second thing is to setup version control on the front end    The way I have done that in a lot of my databases is to have the users run a small    jumper    database to open the main database  This jumper does the following things        Checks to see if the user has the database on their C drive        If they do not then install and run        If they do then check what version they have        If the version numbers do not match then copy down the latest version        Open the database  This whole checking process normally takes under half a second  Using this model you can do all your development on a separate database then when you are ready to    release    you just put the new mde up onto the network share and the next time the user opens the jumper the latest version is copied down   There are also other things to think about in multiuser database and it might be worth checking for the common mistakes such as binding a form to a whole table etc

User · Answer

The correct way of building client server Microsoft Access applications where the data is stored in a RDBMS is to use the Linked Table method  This ensures Data Isolation and Concurrency is maintained between the Microsoft Access client application and the RDBMS data with no additional and unnecessary programming logic and code which makes maintenance more difficult  and adds to development time   see  http   claysql blogspot com 2014 08 normal-0-false-false-false-en-us-x-none html

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