There are quite a few things that can affect the load rate. I am no expert on Oracle, but these are some of the things which generally affect relatove database table performance
- Select * loads all fields in the table. The 800 records per second table might have a row size that is substantially larger than the second. Check the record size for each table in the databse table definitions.
- Indexing and keys. If the table is a virtual table or a view, the indexing on the underlying table has a huge affect on performance. As would joins within a view.
- Fragmentation in the database. If one table is updated more frequently than the other, then that table could become fragmented, affecting read performance.
- Concurrency. If other users are on the database, they might be affecting performance through locking and transactions taking place on the slower performing table.
- Calculated fields and read triggers also cause extra overhead on reading.
There may be others, but these are the ones that come immediately to mind.