Full vs Incremental Refresh?

What is the main difference between full an incremental (auto)refreshes?
Documentation suggests that full refresh is recommended on the groups when data is changing very frequently while Incremental refresh is advised to use on the tables when data is more or less static.
1. Is there any way to justify/quantify what is the frequent data change (50% of records in 24 hours, etc..)?
2. In the documentation I also found that using Incremental Data Refresh TT will hook up triggers on the tables in the Oracle DB. Is that correct?
3. For Full DataRefresh TT will be using logs from Oracle DB to refresh the data in TT. In some cases logs in the Oracle DB are kept only for a specific number of days (i.e. 5 days). What will happen if those logs are not available?
4. Using Full refresh TT will be reloading all the data from the Oracle DB. Is there any impact for the data availability in TT by using Full refresh?
5. I believe that Full data refresh will be taking much more time compared to the Incremental data refresh. In this case if I set autorefresh to every 5 seconds, then basically I will end up with the infinite refresh. What is recommended frequency for Full and Incremental refreshes?
6. Full vs Incremental refresh. Which one is using less resources in Oracle DB and TT and why?
Thank you.

Full refresh works by discarding all the data in the cache group tables and then reloading it all from Oracle on every refresh cycle. it is best when (a) the tables are very small and (b) the refresh interval is not too short.
Incremental autorefresh works by installing a trigger and a tracking table on each of the base tables in Oracle. As changes occur in Oracle they are tracked and when the next autorefrsh cycle comes around only the changes are propagated to the cache tables. Incremental is recommended when (a) the tables involved are of any substantial size and/or (b) when a short refresh interval is required. To try and answer your specific questions:
1. Is there any way to justify/quantify what is the frequent data change (50% of records in 24 hours, etc..)?
CJ>> Not really. This comes down to application requirements, how much load you can tolerate on Oracle etc.
2. In the documentation I also found that using Incremental Data Refresh TT will hook up triggers on the tables in the Oracle DB. Is that correct?
CJ>> Yes, a single trigger and a single tracking will be instantiated on each base table that is cached in cache group that uses incremental autorefresh.
3. For Full DataRefresh TT will be using logs from Oracle DB to refresh the data in TT. In some cases logs in the Oracle DB are kept only for a specific number of days (i.e. 5 days). What will happen if those logs are not available?
CJ>> No. Neither incremental nor full refresh uses Oracle logs. Full refresh simply queries the data in the table and incremental uses a combination of the data in the table and the tracking table.
4. Using Full refresh TT will be reloading all the data from the Oracle DB. Is there any impact for the data availability in TT by using Full refresh?
CJ>> Yes. Using full refresh TimesTen starts by emptying the cache table and so there is a significant impact on data availability. Incremental refresh does not have this issue.
5. I believe that Full data refresh will be taking much more time compared to the Incremental data refresh. In this case if I set autorefresh to every 5 seconds, then basically I will end up with the infinite refresh. What is recommended frequency for Full and Incremental refreshes?
CJ>> regardless of the refresh method chosen you should ensure that the refresh interval is set >> than the time it takes to perform the refresh. Setting it to a shorter value simply resuls in almost cointihnuous refresh and a much heavier load on Oracle. This is especially problematic with full refresh.
6. Full vs Incremental refresh. Which one is using less resources in Oracle DB and TT and why?
CJ>> Again it depends but in general incremental is the preferred choice.
In my experience I have rarely seen anyone use full autorefresh.
Chris

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