What is the right way to work with slick's 3.0.0 streaming results and Postgresql?

Question

I am trying to figure out how to work with slick streaming. I use slick 3.0.0 with postgres driver

The situation is following: server have to give client sequences of da

Answer 1

The "right way" to do streaming with Slick and Postgres includes three things:

1. Must use db.stream()

2. Must disable autoCommit in JDBC-driver. One way is to make the query run in a transaction by suffixing .transactionally.

3. Must set fetchSize to be something else than 0 or else postgres will push the whole resultSet to the client in one go.

Ex:

DB.stream(
  find(0L, 0L)
    .transactionally
    .withStatementParameters(fetchSize = 1000)
).foreach(println)

Useful links:

https://github.com/slick/slick/issues/1038

https://github.com/slick/slick/issues/809

Answer 2

The correct way to stream in Slick is as provided in documentation is

val q = for (c <- coffees) yield c.image
val a = q.result
val p1: DatabasePublisher[Blob] = db.stream(a.withStatementParameters(rsType = ResultSetType.ForwardOnly, rsConcurrency = ResultSetConcurrency.ReadOnly, fetchSize = 1000 /*your fetching size*/).transactionally)