Support for PostgreSQL cursors

[collimarco]

Instead of repeating a complex query (e.g. complex where conditions) on every iteration using “ID grater than”, it would be interesting to use native PostgreSQL cursors.

Using PostgreSQL cursors you avoid repeating the query on the database (you avoid repeating it on each iteration, however if the db session ends, then you need to perform the query again, probably using “ID grater than” in this case).

Related:

• https://github.com/afair/postgresql_cursor
• https://www.postgresql.org/docs/current/sql-declare.html