Does one any having list of bottlenecks and workarounds while migrating data
from Oracle to Postgresql. like what are thing which we can migrate from Oracle database to Postgresql and what we can't?
In general you must be able to migrate pretty much any data type to PostgreSQL. It would be good to understand the data-types specifically used in the to-be-migrated Oracle database and how that would effect Application functionality/performance after migrating to PostgreSQL.
If you can provide details on the specific data-types used by Oracle, then, the required information can be provided. As per my experience as far as data types are concerned, issues generally crop-up around when migrating large object types. Having said that, PostgreSQL is rich in supporting side range of data-types.
Which is the best tool for migration from Oracle to Postgresql?
As already suggested, ora2pg is the best open-source tool.