When opening a database table (on the TABLE tab, in the Content group, on the Open list, click Database Table and select the database to open) you can select Live or Linked options for the connection type. By default, the table opens in MapInfo Pro with live access with caching turned on, so that you access it directly from its source location with the additional speed that caching provides. To change how you access an already open table, you must close it and open it again.
Working with Live Access Database Tables
By default, MapInfo Pro opens database tables using live access. A live connection to a table lets you read data from the database as required. This is helpful when sharing the data with another application, to ensure that you are always working with the latest updates.
You would consider choosing the Live option for accessing a table when:
- Reading and editing dynamically changing data.
- You want to maintain data security (the data must remain only in a single secure location).
For a full list of considerations, see Comparing and Contrasting Live and Linked Access to a Table.
To improve the data access speed with live access tables, you can specify that data be locally cached. MapInfo Pro then reads the table data from the cache. The life of the cache is limited to the current session. Access time to data is faster, but you are not working with the most current version. The table refreshes when you zoom, pan, or select the table data in a Map window, or when you edit the data in a Browser window.
Working with Linked Access Database Tables
You have the option to open a database table as a linked access table. A linked table is a MapInfo Pro table that is a replica of a table downloaded from a remote database and retains links to its remote database table. (The remote table is the database table.) When MapInfo Pro downloads a table, it copies the entire contents of the table to the local machine. Any changes you make to the copy can be committed to the database table at any time. Linked tables can be used stand-alone or remain linked to the original database. After editing data in a linked table, MapInfo Pro saves it to the database in a manner that resolves any multi-user editing conflicts. Saving the edits made to a linked table commits them to the database as well as to the linked table.
You would consider choosing the Linked option for accessing when:
- Using the table contents as backdrop display data, or data that does not change much. Linked tables are editable, as long as the base tables they are based on are editable.
- Tables are very large. As the data is entirely local, there is a one-time cost of downloading the data, but subsequent access is fast, comparable to native table access, since the user does not incur the cost of network traffic every time the data needs to be accessed for mapping, or for analysis.
Linked tables are limited to 2 GB per data file.
Caching Data from Database Tables
By default, data caching is turned on for linked tables. Data caching is not applicable for live access tables.
When cashing data, MapInfo Pro opens a database table and keeps the attributes and objects that have been read in memory. This saves time redrawing the map and processing the data when performing an operation, such as zooming in or out on a map, because the attributes do not need to be fetched from the database.
When caching data from a linked table, MapInfo Pro looks in memory for a record, so you may not see the latest updates made to the database table. Another user's updates may not appear until the cache is invalidated by a pan or zoom out operation.
When not cashing data from a linked table, MapInfo Pro retrieves all of the data from the database whenever it is needed. This provides the most current data but it is less efficient then caching the data.
You can turn caching off for linked tables in the Select One or More Tables to Open dialog box:
- For multiple tables, select the tables that you want to open and then click Cached (so that the button in the Select One or More Tables to open dialog box is not selected). This turns off caching for all of the selected tables, except for tables that have override settings.
- For a single table, highlight the table name in the list and then click Options. In the Open DBMS Table Options dialog, clear the Cache check box. This setting is specific to this table and overrides the setting made by clicking Cached in the Select One or More Tables to Open dialog box.