> E: I don't see in the article when rows get evicted from the undo logs. The undo records are truncated once they aren't needed for any transaction. > If whe

> E: I don't see in the article when rows get evicted from the undo logs. The undo records are truncated once they aren't needed for any transaction. > If when they are no longer needed, I'm not sure where the improvement comes from because it should be similar amount of bookkeeping? It depends on what exactly is "bookkeeping". If we consider amount of work, then improvement comes because old undo records can be just bulk deleted very cheap (corresponding files get unliked). No vacuum scan is needed. If we consider amount of space occupied, then indeed the same amount of versions take the same amount of space. But saving old versions of rows in the separate storage can save their primary storage from long-term degradation. Also, note that OrioleDB implements automatic merging of sparse pages. > If it's a circular buffer that can ran out of space like Oracle does it that would mean under high write load long-running transactions starts to fail which is pretty unpleasant. OrioleDB implements in-memory circular buffer for undo logs. Once circular buffer can't handle all the undo records, least recent records are evicted to the storage. Currently, we don't place limitation on the site of undo logs. Undo records are kept while any transaction can need them. So, no "Snapshot Too Old" errors. However, we can consider implementing this Oracle-like error as an option, which allows to limit the undo size. Also, please, check the architecture documentation of github (if didn't already). https://github.com/orioledb/orioledb/blob/main/doc/arch.md https://github.com/orioledb/orioledb/blob/main/doc/arch.md