On Wed, 18 Dec 2019 at 23:13, Matthew Phillips <mphillips34@xxxxxxxxx> wrote:
With the current READ UNCOMMITTED discussion happening on pgsql-hackers [1], It did raise a question/use-case I recently encountered and could not find a satisfactory solution for. If someone is attempting to poll for new records on a high insert volume table that has a monotonically increasing id, what is the best way to do it? As is, with a nave implementation, rows are not guaranteed to appear in monotonic order; so if you were to keep a $MAX_ID, and SELECT WHERE p_id > $MAX_ID, you would hit gaps. Is there a clean way to do this? I've seen READ UNCOMMITTED used for this with DB2.
Not sure it helps much. The new records aren't truly there until commit.
Using max_id alone is not an effective technique. It's just an optimization.
Just be careful to not advance max_id too quickly, and remember which ones you've already checked. Or wait for the next monontonic value each time, accepting the lag.
