zlacker

>>hyzyla+(OP)
You really don't need anything fancy to implement a queue using SQL. You need a table with a primary id and a "status" field. An "expired" field can be used instead of the "status". We used the latter because it allows easy retries.

1. SELECT item_id WHERE expire = 0. If this is empty, no items are available.

2. UPDATE SET expire = some_future_time WHERE item_id = $selected_item_id AND expire = 0. Then check whether UPDATE affected any rows. If it did, item_id is yours. If not, loop. If the database has a sane optimizer it'll note at most one document needs locking as the primary id is given.

All this needs is a very weak property: document level atomic UPDATE which can return whether it changed anything. (How weak? MongoDB could do that in 2009.)

Source code at https://git.drupalcode.org/project/drupal/-/blob/9.2.x/core/... (We cooked this up for Drupal in 2009 but I am reasonably sure we didn't invent anything new.)

Of course, this is not the fastest job queue there is but it is quite often good enough.

>>_ugfj+z2
Oh please stop using databases as queues. I spent a disproportionate amount of time in the last 20 years undoing that decision. It doesn’t scale at all well.

>>hughrr+gc
This please. I feel like "How to Get Away with Just PostgreSQL" and the GP comment falls squarely under being too preoccupied with whether you could, you didn't stop to think if you should.

Whatever happened to use the proper data structures for the job? PostgreSQL and MySQL are, at the end of the day, b-trees with indices. Throw in relational properties and/or ACID too. Those aren't properties you need or want in a queue structure.

I know I don't have a solid argument against not doing it; it's just experience (and dare I say, common sense) telling me not to. Not quite like parent but I spent the first two years of my professional career in a team that had the brilliant idea to use DBs as queues. The big task I partook in for that stint is moving them off that v2 into a v3 which used---wait for it---Redis. Everyone's quality of life improved with every migration, proportional to the size of the v2 cluster we retired.

>>skytre+vj
> Whatever happened to use the proper data structures for the job? PostgreSQL and MySQL are, at the end of the day, b-trees with indices. Throw in relational properties and/or ACID too. Those aren't properties you need or want in a queue structure.

How is relational storage engine with support for transactions, document/json, ACID, hot-standby "the wrong data model" for a queue?