`pg-cursor` usage leads to memory leak

[viladimiru]

If you will execute any read query, you can see in node inspector that GC ignores query result and doesn't cleanup it

const client = new PostgreSqlClient({...credentials, query_timeout: 15 * 60_000});
const cursor = client.query(
    new Cursor(query),
    unhandledErrorCallback,
);
await new Promise((resolve, reject) => {
  cursor.read(100000, (error, _, result) => {
      if (error) {
          reject(error);
      } else {
          resolve(result);
      }
  })
})

This happens because of the callback with timeout cleanup:
https://github.com/brianc/node-postgres/blob/master/packages/pg/lib/client.js#L577
query.callback will not be called even if you closed cursor and destroyed the client

[viladimiru]

Quick fix

const client = new PostgreSqlClient({...credentials, query_timeout: 15 * 60_000});
const cursor = client.query(
    new Cursor(query),
    queryCallback, // will be called in `cursor.callback()`
);
await new Promise((resolve, reject) => {
  cursor.read(100000, (error, _, result) => {
      if (error) {
          reject(error);
      } else {
          resolve(result);
      }
  })
})

// this way we call method, which responsible to clear timeout
// https://github.com/brianc/node-postgres/blob/master/packages/pg/lib/client.js#L576
cursor.callback();

[brianc]

hmmm I'm not sure mixing callbacks & promises here is the right approach. I've never seen a 2nd argument (callback) passed to client.query when a cursor is passed as the first argument. Sorry for being dumb about this but what are you trying to accomplish w/ that approach?