05 October 2010

The Limitations of MS Access Database

    In the previous post I was highlighting some general considerations on the use of MS Access and Excel as frameworks for building applications. I left many things out from the lack of time and space, therefore, as the title reveals, in this post I will focus simply on the limitations of MS Access considered as Database. I considered then that Access is a fairly good as database, recommending it for 10-20 concurrent users, fact that could equate, after case, maybe with a total of users that range between 1-100. Of course, this doesn’t mean that MS Access can’t do more, actually it supports 255 concurrent users and with a good design that limit could be reached.

   Another important limitation regards the size of an Access database, set to 2GB, it used to be more than sufficient a few years back, though nowadays, it’s sometimes the equivalent of a month/year of transactions. I never tried to count how many records could store a MS Access, though if I remember correctly, a relatively small to average table of 1000000 (10^6) records occupies about 100MB, using this logic 2GB could equate with about 20000000 (2*10^7) records, the equivalent of a small to average database size. Anyway, the numbers are relative, the actual size depends also on the number of objects the database stores, the size of attributes stored, on the fact that even if Access is supposed to have a limitation of 2GB, I met cases in which a database of 1GB was crashing a lot, needing to be repaired or backed up regularly. Sometimes it could be repaired, other times not, unfortunately the “recovery” built within a MS Access can’t be compared with the recovery available in a RDBMS. That’s ok in the end, even mature databases crash from time to time, though the logs and transaction isolation models allow them to provide high recoverability and reliability, to which adds up scalability, availability, security and manageability. If all these are not essential for your database solution, the MS Access is ok, though you’ll have to invest effort in each of these area when you have to raise your standards.

    One of the most painful issues when dealing with concurrent data access is the transaction processing that needs to guarantee the consistency and recoverability of operations. As Access is not handling the transactions, the programmer has to do that using ADO or DAO transactions. As many applications still don’t need pessimistic concurrency, with some effort and a good row versioning also this issue could be solved. Also the security-related issues could be solved programmatically by designing a role-based permission framework, though it occasionally it could be breached when the user is aware of the few Access hacks and has direct access to the database. Manageability resumes usually in controlling resources utilization, monitoring the progress of the actions running on the database. If Access is doing a relatively good job in what concerns the manageability of its objects, it has no reliable way to control their utilization, when a query is running for too long, the easiest way to solve this is to coldly kill the process belonging to Access. Not sure if it makes sense to philosophy about Access’ scalability and availability, at least can’t be comparable from this point of view with RDBMS for which failover clustering, mirroring, log shipping, online backup and in general online maintenance have an important impact on the two.

   Excepting the above theoretical limitations, when MS Access is part of your solution, it’s always a good idea to know its maximal capacity specifications, this applying to all type of databases or technologies.  Most probably you won’t want that in the middle of your project or even later you realize that you reach one of such limitations. I tried to put together a comparison between the maximal capacity specifications for 2000, 2007 and 2010 versions of MS Access and, for reference, the same specification for SQL Server (2000, 2005, 2008 R2). The respective information come mainly from Microsoft websites, with a few additions from [5] and [6].

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MS Access

SQL Server

Attribute

2000 [1]

2007/2010 [2]

2000 [7]

2005 [4]

2008 R2 [3]

 SQL statements size

64kb

64kb

64kb

64kb

64kb

# characters in Memo field

65535

65535

-

2^30-1
2^31-1

# characters in Text field

255

255

8000

8000
8000

# characters in object name

64

64

128

128

128

# characters in record

4000

4000

8000

8000
8000

# concurrent users

255

255

 

 

32767

# databases per instance

1

1

32767

32767

32767

# fields in index

10

10

16

16

16

# fields in recordset

255

255

4096

4096

4096

# fields in table

255

255

1024

1024

1024/30000

# files per database

1

1

32767

32767

32767

# forced relationships per table

32

32

253

253

253

# indexes per table

32

32

250 (1 clustered)

250 (1 clustered)

250 (1 clustered)

# instances

 

 

16

50

50

# joins in a query

16

16

32

32

32

# levels nested queries

50

50

32

32

32

# nested subqueries

 

 

32

32

32

# objects

32768

32768

2147483647
<>

2147483647

2147483647

# open tables

2048

2048

2147483647

2147483647

2147483647

# roles per database

n/a

n/a

16379

16379

16379

# tables in a query

32

32

256

256

256

# users per database

n/a

n/a

16379

16379

16379

database size

<2GB

<2GB

1048516 TB

542272TB

542272TB

file size (data)

2GB

2GB

32TB

16TB

16TB

file size (log)

n/a

n/a

32TB

2TB

2TB

 

     For my surprise the maximal capacity specifications of Access are comparable with the ones of SQL Server for many of the above attributes. Sure, there is a huge difference in what concerns the number of databases, the database/file size and the number of supported objects, quite relevant in the architecture of applications. Several other differences, for example the number of indexes supported per table or relationships per table, are less important for the majority of solutions. Another fact that is not remarked in the above table is the fact that the number of records in a table are typically limited by storage. Please note that many important features not available in Access were left out, therefore, for a better overview is advisable to check directly the referenced sources.

 

   There are two one more personal observations for this post. Even if MS Access is great for non-SQL developers giving its nice Designer, for SQL developers it lacks a rich editor, the initial formatting being lost, this doubled by the poor support for later versions of the ANSI standard make from Access a tool to avoid.

 

References:
[1] Microsoft. 2010. Microsoft Access database specifications. [Online] Available form:
http://office.microsoft.com/en-us/access-help/access-specifications-HP005186808.aspx (Accessed: 04.10.2010)

[2] Microsoft. 2010. Access 2010 specifications [Online] Available form: http://office.microsoft.com/en-us/access-help/access-2010-specifications-HA010341462.aspx (Accessed: 04.10.2010)
[3] MSDN. (2010). Maximum Capacity Specifications for SQL Server: SQL Server 2008 R2. [Online] Available form: http://msdn.microsoft.com/en-us/library/ms143432.aspx (Accessed: 04.10.2010)

[4] MSDN. (2010). Maximum Capacity Specifications for SQL Server: SQL Server 2005. [Online] Available form: http://msdn.microsoft.com/en-us/library/ms143432(SQL.90).aspx (Accessed: 04.10.2010)

[5] SQL Server Helper. (2005). SQL Server 2005: Maximum Capacity Specifications. [Online] Available form: http://www.sql-server-helper.com/sql-server-2005/maximum-capacity-specifications.aspx (Accessed: 04.10.2010)

[6] MSDN. (2008).SQL 2005 and SQL 2008 database volume capacity. [Online] Available form: http://social.msdn.microsoft.com/forums/en-US/sqlgetstarted/thread/4225734e-e480-4b21-8cd4-4228ca2abf55/ (Accessed: 04.10.2010)

[7] MSDN. (2010). Maximum Capacity Specifications for SQL Server: SQL Server 2000. [Online] Available form: http://technet.microsoft.com/en-us/library/aa274604(SQL.80).aspx (Accessed: 04.10.2010)

[8] MSDN. (2010). Comparison of Microsoft Access SQL and ANSI SQL. [Online] Available form: http://msdn.microsoft.com/en-us/library/bb208890.aspx (Accessed: 04.10.2010)

1 comment:

Anonymous said...

You forgot to mention that Access can migrate to a SQL Express database. As of the SQL 2008 R2 release, the database file size limit has gone to 10GB

http://www.microsoft.com/express/Database/