Hi all, I'm sorry at first for numberless questions recently :(
If AWT cache group is replicated by an active standby pair and behind standby database there are two read-only subscribers,
will query on read-only subscribers be passed through to the backend oracle database if no rows found?
In other words, could read-only subscribers talk to the backend oracle database just like active or standy database?
Firstly, we need to be careful of terminology to avoid lots of confusion.
Pass-through is a TimesTen feature which allows queries and DML to be re-directed to the backend Oracle DB is (a) the query uses syntax not understood by TimesTen, (b) the query references one or more tables that are not cached in TimesTen or (c) the user has explicitly asked for the query/DML statement to be 'passed through'. Pass-through has nothing to do with finding or not finding rows to match a query/DML operation.
I beliefe what you are referring to is 'dynamic load' where, for a cache group declared as 'dynamic' (e.g. CREATE DYNAMIC ASYNCHRONOUS WRITETHROUGH CACHE GROUP ...), TimesTen will, on a 'no rows found' condition, for certain classes of query/operation, then go an look in Oracle DB.
When replicating cache groups using A/S pair replication, the cache tables and cache groups are present in both masters (active and standby) as actual cache groups and cache tables. If replication readonly subscribers are used, any cache tables are present there as regular tabels, not cache tables. So DYNAMIC LOAD is not available for queries in readonly subscribers. EVen if the tables were present as cache tabels / cache groups it would still not be possible since by definition these subscribers are readonly and dynamic load implies modification to the tables (the dynamically loaded rows must be inserted). The Pass-through feature is available at read-only subscribers.
I hope that clarifies.