This issue was reported by Alexey Kamenchuk on rhq-users.org.  He explains that he is not able to auto-discovery his postgres resources, and that he has well over 100 to find and import.  His workaround is to navigate to each platform and perform a "manual add" on each, adding the connection property details for each, but this is of course rather tedious.  His agent log shows the following:

2010-06-21 12:09:09,271 INFO  [InventoryManager.discovery-1] (rhq.core.pc.inventory.AutoDiscoveryExecutor)- Process scan auto-detected new server resource: scan=[ProcessScan: query=[process|basename|match=^(postgres|postmaster)$,process|basename|nomatch|parent=^(postgres|postmaster)$], name=[unix]], discovered-process=[process: pid=[20646], name=[/data/pgsql/bin/postgres], ppid=[1]]                                                                                                                                                                               
2010-06-21 12:09:09,292 INFO  [ResourceDiscoveryComponent.invoker.daemon-2] (org.rhq.plugins.postgres.PostgresDiscoveryComponent)- Discovered a postgres process: ProcessScanResult: scan=[
ProcessScan: query=[process|basename|match=^(postgres|postmaster)$,process|basename|nomatch|parent=^(postgres|postmaster)$], name=[unix]], info=[process: pid=[20646], name=[/data/pgsql/bi
n/postgres], ppid=[1]]                                                                                                                                                                    
2010-06-21 12:09:09,344 INFO  [ResourceDiscoveryComponent.invoker.daemon-2] (org.rhq.plugins.postgres.PostgresDiscoveryComponent)- Failed to connect to the database                      
org.postgresql.util.PSQLException: FATAL: password authentication failed for user "postgres"                                                                                              
        at org.postgresql.core.v3.ConnectionFactoryImpl.doAuthentication(ConnectionFactoryImpl.java:291)                                                                                  
        at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:108)                                                                                
        at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:66)                                                                                                
        at org.postgresql.jdbc2.AbstractJdbc2Connection.<init>(AbstractJdbc2Connection.java:125)                                                                                          
        at org.postgresql.jdbc3.AbstractJdbc3Connection.<init>(AbstractJdbc3Connection.java:30)                                                                                           
        at org.postgresql.jdbc3.Jdbc3Connection.<init>(Jdbc3Connection.java:24)                                                                                                           
        at org.postgresql.Driver.makeConnection(Driver.java:393)                                                                                                                          
        at org.postgresql.Driver.connect(Driver.java:267)                                                                                                                                 
        at java.sql.DriverManager.getConnection(DriverManager.java:582)                                                                                                                   
        at java.sql.DriverManager.getConnection(DriverManager.java:185)                                                                                                                   
        at org.rhq.plugins.postgres.PostgresDiscoveryComponent.buildConnection(PostgresDiscoveryComponent.java:195)                                                                       
        at org.rhq.plugins.postgres.PostgresDiscoveryComponent.getConnection(PostgresDiscoveryComponent.java:259)                                                                         
        at org.rhq.plugins.postgres.PostgresDiscoveryComponent.createResourceDetails(PostgresDiscoveryComponent.java:150)                                                                 
        at org.rhq.plugins.postgres.PostgresDiscoveryComponent.discoverResources(PostgresDiscoveryComponent.java:123)                                                                     
        at sun.reflect.GeneratedMethodAccessor37.invoke(Unknown Source)                                                                                                                   
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)                                                                                          
        at java.lang.reflect.Method.invoke(Method.java:597)                                                                                                                               
        at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ComponentInvocationThread.call(DiscoveryComponentProxyFactory.java:266)                                                    
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)                                                                                                             
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)                                                                                                                       
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)                                                                                            
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)                                                                                                
        at java.lang.Thread.run(Thread.java:619)                                                                                                                                          
2010-06-21 12:09:09,345 WARN  [InventoryManager.discovery-1] (rhq.core.pc.inventory.InventoryManager)- Failure during discovery for [Postgres Server] Resources - failed after 56 ms.     
java.lang.Exception: Discovery component invocation failed.                                                                                                                               
        at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ComponentInvocationThread.call(DiscoveryComponentProxyFactory.java:270)                                                    
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)                                                                                                             
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)                                                                                                                       
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)                                                                                            
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)                                                                                                
        at java.lang.Thread.run(Thread.java:619)                                                                                                                                          
Caused by: java.lang.NullPointerException                                                                                                                                                 
        at org.rhq.plugins.postgres.PostgresDiscoveryComponent.getDatabaseNames(PostgresDiscoveryComponent.java:277)                                                                      
        at org.rhq.plugins.postgres.PostgresDiscoveryComponent.getServerResourceName(PostgresDiscoveryComponent.java:295)                                                                 
        at org.rhq.plugins.postgres.PostgresDiscoveryComponent.createResourceDetails(PostgresDiscoveryComponent.java:151)                                                                 
        at org.rhq.plugins.postgres.PostgresDiscoveryComponent.discoverResources(PostgresDiscoveryComponent.java:123)                                                                     
        at sun.reflect.GeneratedMethodAccessor37.invoke(Unknown Source)                                                                                                                   
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)                                                                                          
        at java.lang.reflect.Method.invoke(Method.java:597)                                                                                                                               
        at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ComponentInvocationThread.call(DiscoveryComponentProxyFactory.java:266)                                                    
        ... 5 more                      

Looking at SCM history, it shows me the createResourceDetails method of the PostgresDiscoveryComponent was altered to obtain a more accurate/descriptive server resource name.  However, this new piece of code requires a live connection to the PG instance, which won't work if the user has changes the default PWD for 'postgres' user.

So the connection to the PG server fails, returns a null Connection object, which then causes NPE later in the workflow.  This NPE is then uncaught and bubbles out of createResourceDetails, which rolls back the discovery of that PG server.  Effectively the only way to add a PG server with non-default credential now is to go to the platform and manually add it.

I think we need a reasonable fallback mechanism to allow discovery no matter what.