README.md

cursors

This subproject shows how to use a Postgres cursor to iterate over a result set from Java code.

Follow these instructions to run the demo.

Start the Postgres database:

docker compose up --renew-anon-volumes --detach

Run the program:
- ```
./gradlew run
```
- Study the logs that are printed to the console. It shows that the program makes a new fetch request to the database between each "destination" that is visited. So, it is using a cursor!
Run the tests:
- ```
./gradlew test
```
Stop the database:
- ```
docker compose down
```

Postgres docs: Cursors

Rather than executing a whole query at once, it is possible to set up a cursor that encapsulates the query, and then read the query result a few rows at a time. One reason for doing this is to avoid memory overrun when the result contains a large number of rows.
Postgres JDBC docs: Chapter 5. Issuing a Query and Processing the Result

By default the driver collects all the results for the query at once. This can be inconvenient for large data sets so the JDBC driver provides a means of basing a ResultSet on a database cursor and only fetching a small number of rows.