SSIS, query Oracle table using ID's from SQL Server? - sql-server

Question

Here's the basic idea of what I want to do in SSIS:
I have a large query against a production Oracle database, and I need the following where clause that brings in a long list of ids from SQL Server. From there, the results are sent elsewhere.
select ...
from Oracle_table(s) --multi-join
where id in ([select distinct id from SQL_SERVER_table])
Alternatively, I could write the query this way:
select ...
from Oracle_table(s) --multi-join
...
join SQL_SERVER_table sst on sst.ID = Oracle_table.ID
Here are my limitations:
The Oracle query is large and cannot be run without the where id in (... clause
This means I cannot run the Oracle query, then join it against the ids in another step. I tried this, and the DBA's killed the temp table after it became 3 TB in size.
I have 160k id's
This means it is not practical to iterate through the id's one by one. In the past, I have run against ~1000 IDs, using a comma-separated list. It runs relatively fast - a few minutes.
The main query is in Oracle, but the ids are in SQL Server
I do not have the ability to write to Oracle
I've found many questions like this.
None of the answers I have found have a solution to my limitations.
Similar question:
Query a database based on result of query from another database

Answer 1

To prevent loading all rows from the Oracle table. The only way is to apply the filter in the Oracle database engine. I don't think this can be achieved using SSIS since you have more than 160000 ids in the SQL Server table, which cannot be efficiently loaded and passed to the Oracle SQL command:
Using Lookups and Merge Join will require loading all data from the Oracle database
Retrieving data from SQL Server, building a comma-separated string, and passing it to the Oracle SQL command cannot be done with too many IDs (160K).
The same issue using a Script Task.
Creating a Linked Server in SQL Server and Joining both tables will load all data from the Oracle database.
To solve your problem, you should search for a way to create a link to the SQL Server database from the Oracle engine.
Oracle Heterogenous Services
I don't have much experience in Oracle databases. Still, after a small research, I found something in Oracle equivalent to "Linked Servers" in SQL Server called "heterogeneous connectivity".
The query syntax should look like this:
select *
from Oracle_table
where id in (select distinct id from SQL_SERVER_table#sqlserverdsn)
You can refer to the following step-by-step guides to read more on how to connect to SQL Server tables from Oracle:
What is Oracle equivalent for Linked Server and can you join with SQL Server?
Making a Connection from Oracle to SQL Server - 1
Making a Connection from Oracle to SQL Server - 2
Heterogeneous Database connections - Oracle to SQL Server
Importing Data from SQL Server to a staging table in Oracle
Another approach is to use a Data Flow Task that imports IDs from SQL Server to a staging table in Oracle. Then use the staging table in your Oracle query. It would be better to create an index on the staging table. (If you do not have permission to write to the Oracle database, try to get permission to a separate staging database.)
Example of exporting data from SQL Server to Oracle:
Export SQL Server Data to Oracle using SSIS
Minimizing the data load from the Oracle table
If none of the solutions above solves your issue. You can try minimizing the data loaded from the Oracle database as much as possible.
As an example, you can try to get the Minimum and Maximum IDs from the SQL Server table, store both values within two variables. Then, you can use both variables in the SQL Command that loads the data from the Oracle table, like the following:
SELECT * FROM Oracle_Table WHERE ID > #MinID and ID < #MaxID
This will remove a bunch of useless data in your operation. In case your ID column is a string, you can use other measures to filter data, such as the string length, the first character.