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Remember that time is also a dimension and you might need to store historic data as well. Read Data Normalization Fundamentals for more detail.
This allows your database application to quickly locate specific records. Primary Key Should be One Field and Numeric The primary key should only be one field and ideally numeric and meaningless.
Primary keys define the uniqueness of each record, which can be accomplished efficiently with a single number.
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The primary key is also used in each secondary index for that table, so the smaller the better. Multi-field primary keys and non-numeric text fields are less desirable.
For example, a list of countries or states is a good candidate because there is no need to create a separate number for each country or state. Having a meaningless primary key means that the index is stable even when data changes. Otherwise, changes in the primary key have a ripple effect through each secondary index and any other tables bound by referential integrity.
With cascading deletes, the removal of the parent record automatically deletes the child records in the corresponding table. Access the Jet Engine automatically takes care of this for you without the need to write any code, which is great for maintaining data integrity.
With a relationship established, a hidden index is created for the foreign key, so links between those tables are faster in queries. The link is also automatically drawn for you when you put the two tables on your query designer. Eliminate Unnecessary Subdatasheets By default, Access creates subdatasheet views between related tables. This is nice if you want it, but is a huge performance hit every time you open the table. Here is more information on the Subdatasheet Name Property.
Choose the Optimal Data Types Choose the best data types for your fields. By choosing the optimal data type, you can decrease both the disk space used to store data, and the time it takes Access to retrieve, manipulate, and write data. The general guideline is to choose the smallest data type possible to store a particular type of data. Add Secondary Indexes as Necessary If your tables are large and you search on a field or use it in a join, create a secondary index on the field s.
Secondary Indexes offer performance gains on an order of magnitude. Every index adds to the time it takes the database engine to update, delete and add records. To check the number of unique entries in an index, use the Access DistinctCount property.
Compare this value to the number of records in the table and you can quickly see if the index is doing you any good. Keep Indexes As Small As Possible When creating a multi-field index, index only as many fields as are absolutely necessary.
Keep this variable open as long as your application is running. This forces Access to keep that database open, making access to linked tables much faster. For more information, see Increasing the Performance of Linked Databases. Minimize Record Navigation Avoid record navigation wherever possible on linked tables. This data access method is more efficient for adding records because existing records are not read from the database.
This prevents Access from attempting to retrieve all the existing records in a linked table when you need to add new records. Limit the Data Returned by Queries Limit the number of fields and records returned by using filters or queries. This reduces the amount of data that needs to be read from the linked table, thereby according faster performance. Release Locks ASAP To improve multi-user concurrency, assume that other users will try to edit data in the same linked tables that you use.
In other words, keep records locked only as long as is necessary. This makes opening that table much faster in subsequent attempts. This is because linked tables cache a lot of information about the source table in your database, making the retrieval of the same structural information unnecessary after the linked table is created.
Minimize Server Traffic Minimize the amount of data returned from the server. Do this by structuring your queries to return only the fields and records needed. Instead, consider using Snapshot recordsets, which can be faster to scroll through. Of course, Snapshot recordsets can take longer to open since they require a full read of the source data.
Snapshot type recordsets must load all records from the data source before becoming available, whereas Dynasets are available as soon as the first 20 or so records are retrieved. Also, when using a Snapshot against large ODBC data sources, you run the risk of running out of disk space on your local computer.
Then, the database engine creates a temporary database to store the contents of the snapshot. In a nutshell, when you open a snapshot, you need at least as much disk space as the largest table you are opening. Microsoft Access forms and reports have automatic caching mechanisms. The following query operations force the Jet database engine to perform local data processing: Join operations between tables that are linked to different data source that is, a join between a SQL table and a linked Access table.
Outer joins that contain syntax that is not directly supported by the remote database server. Database Performance Tips Split Your Database into Two Databases You can improve performance and application maintainability by splitting your Access database into two databases.
The "application" part of your database holds all objects except tables, and is linked to the "data" part that contains the actual tables. MDA created with a previous version of MS Access, convert it to the current version of Access for optimum performance. Use the Access Performance Analyzer Microsoft Access has a useful performance tool built right into the product. From the Tools menu, select Analyze, Performance.
Use the Performance Analyzer to select all objects or specific objects, and then run an analysis that looks for potential problems. The Performance Analyzer does not find all of the items that Total Access Analyzer does, but it does offer some tips. Run the Access Table Analyzer The Access Table Analyzer makes it easy to properly normalize the data in your tables by breaking tables with repeated or improperly structured data into two or more tables.
This tool is available from the Access Tools, Analyze menu Reduce the Size of Graphics in your Access Databases If you embed graphics on your forms or reports, Access can store them much more efficiently. Access can convert graphics into much smaller PNG formats to significantly reduce the size of your databases.
This does not affect graphics already on your forms and reports but helps if you add new graphics or replace existing ones. To activate this feature, change an Access setting. At the bottom of the Application Options section, set the Picture Property Storage Format to Preserve source image format smaller file size. You should do this on a regular basis. Also, be sure to compact anytime you import or delete objects in your database, or compile and save VBA code. Learn more about Total Visual Agent for a system administrative tool to schedule compact and backup your Access databases on a regular schedule.
Make It Look Faster If you have exhausted all other performance optimization techniques, consider making your application "look" faster. Do this by displaying status messages and progress meters as your application loads forms, runs queries, and performs any other operation that might take a bit of time. When you compact the database, you reorganize records so that they are stored in adjacent spaces, making retrieval faster.
Additionally, compacting a database updates its data statistics, which can be used by a query to run faster.
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You can force a query to recompile which in turn causes it to use the latest statistics by opening it in design view, saving it, and then running it. You might want to defragment your disk by using a program such as the Disk Defragmenter that is part of Windows before you compact your database. This leaves contiguous free disk space immediately after the database file.
In theory, this makes future additions to the database occur faster. You might want to experiment with this on your system. Index the fields on both sides of a join. Alternatively, you can create a relationship between joined fields, in which case an index is automatically created. Use Identical or Compatible Datatype in Join Fields Fields that are joined in a query should have the same data type, or compatible data types. For example, the Long Integer data type is compatible with the AutoNumber data type.
Limit Fields Returned by a Query Where possible, limit the number of fields returned by a query. This results in faster performance and reduced resource usage.
Pay special care to avoid the use of immediate If IIF functions in sub-queries. Index Sort Fields Index any fields you use for sorting. Be careful not to over-index. Use Temporary Tables to Eliminate Running the Same Queries Over and Over If you are processing data that is used multiple times on multiple reports for example , it might be faster to store intermediate results in temporary tables rather than running a series of Select queries many times.
Create a temporary table to store your results. Empty the table and fill it with your data by using an Append query. You can then use that table for multiple reports and forms. Avoid Domain Aggregate Functions on Foreign Tables Do not use domain aggregate functions DLookup for example in queries to access data from a table that is not in the query. Link to the table and set criteria accordingly, or create a separate aggregate totals query.
Compile Each Query before Delivering Your Application When you compact your database, its data statistics are updated. This sequence of events results in the fastest possible query. Before you deliver your application, compact the database, and then force each query to be recompiled. Other linked data types do not support Rushmore optimization. Link on Primary Key Indexes Whenever Possible To make queries run faster, you should have indexes on all fields in the query that join, restrict, or sort the data.
Whenever possible, link on Primary Key fields instead of other fields. Indexes are most critical on tables with large numbers of records, so you might not see a difference on small tables.
Experiment with One-to-Many Restrictions If you have a one-to-many join in a query with a restriction, try moving the restriction to the other side of the join. For example, if the restriction is on the many side, move it to the one side.