DBMS: Live vs Linked tables
Alex Eastwood
looking for some information regarding working with database tables as live or linked, pros and cons type stuff. I've read through
MapInfo Professional 12.0 - working with spatial databases where it is mentioned that the topic will be covered in a later issue, does anyone know where I can find it? I'm on the site that links to all the archived articles but don't know which one I'm looking for.
Thanks,
Alex
Peter Horsbøll Møller
That could be a good topic for an article, absolutely.
Until we get than one written, have a look at the presentation I used at the User Group meeting in London a couple of years back.
This also covers the differences, pro and cons of the Live, Live with Cache and Linked tables.
You can find the presentation here: https://www.slideshare.net/peterhorsbollmoller/mapinfo-professional-120-and-sql-server-2008
Go to slide 48
Generally speaking there is a few considerations to make:
- Heavy querying -> Linked
- Volatile data -> Live (With Cache)
- High Security -> Live (With Cache) – required log on to the database every time
- Static data -> Linked, if it only changes once a day, once a week, once a month, once a year
If you have specific questions, don’t hesitate to ask
Peter Horsbøll Møller
Pitney Bowes
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Alex Eastwood
as always, thank you for your help. I think the slides contain enough information for now, but we're working on a fairly major MapInfo-to-PostGreSQL/PostGIS rewrite so might well have some more specific questions to add in due course.
Cheers,
Alex
Alex Eastwood
further to the above, does anyone know whether the Live/Linked characteristics are any different if it's a view instead of a table? Probably more a question for database admins...
Cheers,
Alex
Cliff B
As best I could workout, Linked keeps a local copy of the entire table and only refreshes when you tell it to. Linked - Cached is the same but polls for changes from the server before and after each save, and live fetches only the records in the view port and doesn't cache.
Linked is good for large fairly static datasets
Linked Cached is better for large datasets you're editing
and Live is good for frequently changing data, small datasets or datasets where the map will only show a small number of records.
If you have a large dataset and only want a small number of records to query or edit, you can alter the select query of a live tab file using the target database's native SQL so long as its also includes the mi_prinx (or what ever the unique identifer is) and isnt a one to many join you can work with that and still have good performance and flexibility
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Cliff
Alex Eastwood
thank you for your response and providing some specific examples. Since I'll be playing around with various settings and different size tables I will try and post any updates to this thread as and when.
Cheers,
Alex