To make sure the reporting db (ASE3) is always downstream from your WS pair ... regardless of which is the primary (ASE1 vs ASE2), you'd want to setup a MSA off of the ASE1/ASE2 logical db handle.
Let's say you have transactions flowing in the following direction in your WS setup?
ASE1.pubs1 --> (WS) LS1.pubs1 --> ASE2.pubs1
Where 'LS1.pubs1' is the name of your WS/logical connection.
After a 'switch active' your flow of transactions looks like:
ASE1.pubs1 <-- (WS) LS1.pubs1 <-- ASE2.pubs1
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I'm assuming that under both of the above scenarios you always want a copy of all transactions to also flow into the reporting db (ASE3). If this is the case, then you'll want to set up MSA replication from the LS1 logical connection to ASE3. So the above scenarios would become:
ASE1.pubs1 --> (WS) LS1.pubs1 --> ASE2.pubs1
|
|-- (MSA) --> ASE3.pubs1
After a 'switch active' your flow of transactions looks like:
ASE1.pubs1 <-- (WS) LS1.pubs1 <-- ASE2.pubs1
|
|-- (MSA) --> ASE3.pubs1
If this represents what you want, they you would want to setup MSA like follows:
- create a MSA/database repdef with LS1.pubs1 as the PDB
- create a MSA/database subscription with ASE3.pubs1 as the RDB
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I would highly recommend that you routinely test the 'switch active' command (at least in a test env) so that you understand how it works, and to get used to troubleshooting it if there are any hiccups/issues during the switch.
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While there's nothing technically wrong with using WS, over the years I've had intermittent issues with the 'switch active' command failing part through its process, which in turn becomes a major pain in the arse to fix as there are a lot of steps that 'switch active' performs under the covers (and inevitably the problems occur in a PROD environment when I have little time to address/fix the issue ... can you say high stress? :-)
Soooo, I would also recommend you give some thought to replacing the WS configuration with a pair of MSA repdef/subs.
Luc Van der Veurst had a great write-up on why/how he converted all of his WS configs to MSA. You can see his write-up in this thread: Delayed replication of 4 hours and no delay? (scroll down about half way to find Luc's post)