On 12/28/17 11:36, Konstantin Knizhnik wrote: > Attached please find new version of AS OF patch which allows to specify > time travel period. > Older versions outside this period may be reclaimed by autovacuum. > This behavior is controlled by "time_travel_period" parameter.
So where are we on using quasi SQL-standard syntax for a nonstandard interpretation? I think we could very well have a variety of standard and nonstandard AS OF variants, including by commit timestamp, xid, explicit range columns, etc. But I'd like to see a discussion on that, perhaps in a documentation update, which this patch is missing. I have questions about corner cases. What happens when multiple tables are queried with different AS OF clauses? Can there be apparent RI violations? What happens when the time_travel_period is changed during a session? How can we check how much old data is available, and how can we check how much space it uses? What happens if no old data for the selected AS OF is available? How does this interact with catalog changes, such as changes to row-level security settings? (Do we apply the current or the past settings?) This patch should probably include a bunch of tests to cover these and other scenarios. (Maybe "period" isn't the best name, because it implies a start and an end. How about something with "age"?) -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
