Under what circumstances would a server submit new work to a miner?

Question

This is asked in a context to better understand why a submitted share by a miner might be rejected.

I know when a new block gets solved that would require a work update, which is approximately every 10 mins on average. Are there any other circumstances where miners in a pool would get new work from the pool server?

I'm mainly asking this question to better understand the explanation given here:

The cause of this problem is low overall hashrate. Phoenix maintains a work queue to reduce hashrate disruptions caused by momentary connection problems. This works great on faster hardware like the ATI 5870, but it can cause issues with miners that get <100 Mhash or so. The reason for "unknown-work" rejects is that those shares were from work that has been sitting in the queue for long periods of time(>1 min). Some pools "forget" about assigned work after very short time periods (1 minute for example) and any results returned based on that work are rejected as unknown...

It sounds like a pool ignores submitted shares that's over a 1 min even if no new blocks were solved in that time. The submitted share clearly shouldn't be considered stale yet so why would a pool do this?

Answer 1

The problem you are describing could be due to pool optimisation, as it is easier to prune 1 minute old shares than probably it is to look through 10 minutes of shares in order to validate them.

As for why a miner would request new work from a pool, other than as a result of longpolling or finishing a work, might be due to the work becoming invalid with time (with standard protocol a miner would request work every second). Alternatively, the miner is trying to be malicious and trying to make the pool do extra work.