How data is populated to catA and catB

Question

Hi  Guys
If i modify any data in bcc and deploy the project
then how my store app will pick that modified data because  it is pointing to different data source
please clarify my doubt
and also why we have four different data sources instead of one
why some repositories are pointing production datasource and some are pointing to switching data source
please clarify my doubt

Answer 1

There are two data sources live datasource and offline datasource.
Ideally If site points to live datsource, BCC should point to offline datasource.
This can be maintained with initialDataSourceName property in SwitchingDataSource component
Switching datasource deployment:
1. say u have modified ProductCatalog repository and u have two datasouces swticha and switchb.live site server points to switcha and BCC server points to switchb.
2. When project is deployed, It first gets deployed to offline datasouce(switchb)
3. On successful deployment, datasources are switched, ie. site points to switchb(latest database changes reflected on site) and bcc point to switcha.
4. Now project is deployed to switcha, inorder to synchronize both datasouces.
Steps to create switching datasource:
1. Create first datasouce
SwitchingDataSourceA.properties
$class=atg.nucleus.JNDIReference
JNDIName=java:/ATGSwitchingDS_A
2. Create second datasouce
SwitchingDataSourceB.properties
$class=atg.nucleus.JNDIReference
JNDIName=java:/ATGSwitchingDS_B
3. Create switching datasocue compoent
SwitchingDataSource.properties
$class=atg.service.jdbc.SwitchingDataSource
dataSources=\
    DataSourceA=/atg/dynamo/service/jdbc/SwitchingDataSourceA,\
    DataSourceB=/atg/dynamo/service/jdbc/SwitchingDataSourceB
initialDataSourceName=DataSourceA
4. refer this this switching datasouce componet in ur repository.
dataSources=/atg/dynamo/service/jdbc/SwitchingDataSource
Steps to create non-switching datasource:
1. Create first datasouce
JTDataSource.properties
$class=atg.nucleus.JNDIReference
JNDIName=java:/ATGCoreDS_A
2. refer this this non-switching datasouce componet in ur repository.
dataSources=/atg/dynamo/service/jdbc/JTDataSource
why some repositories are pointing production datasource and some are pointing to switching data source?
For any repsository u can configure switching datasource, only catch is it should be modified with BCC, otherwise it won't make any sense to create switching datasource. u can create, but won't be used.
say for order repository, u are not going to modify it from bcc, So it points to default non-switchable datasource(JTDatasource)
but for catalog u can have switching datasouce as mentioned above example of deployment.So u point to switchable datasource(SwitchingDataSource).
Also u can create any number of switching or non-switching datasources for repositories, Just be ready to manage it.say u have requirements to create separate shemaes for Order,Catalog,Core(Rest of ATG Production)
and also why we have four different data sources instead of one
ATG provides followings:
1) SwitchingDataSource:-SwitchingDataSourceA, SwitchingDataSourceB
  default switching datasource for production server components.
2) JTDataSource
  on prodction server: default datasource(non-switching) for production server components.
  on publishig server: default datasource for publishing server components.
3) JTDataSource_production
  on prodction server: no need, If u wish, can point to same schame pointed by JTDataSource.
  on publishig server: default datasource for production server components.
4) JTDataSource_staging
  on publishig server: default datasource for staging server components.
Along with these ATG also provides FakeXADataSource and DirectJTDataSource.
  Which one u were referring?