On Jun 8, 2011 1:49 PM, "Pavan Deolasee" <pavan.deola...@gmail.com> wrote: > > > Hi All, > There is a PROC_IN_ANALYZE flag, but we don't seem to be using it anywhere. Since acquire_sample_rows() returns palloced tuples, can't we let OldestXmin advance after scanning a page by ignoring procs with the flag set, just like we do for PROC_IN_VACUUM ?
I don't even think the pallocing of tuples is a necessary condition. The key requirement is that this process will not access any other tables in this snapshot. In which case we don't need to take it into account when vacuuming other tables. It's not safe to vacuum tuples from the table being analyzed because the vacuum could get ahead of the analyze. This is kind of like the other property it would be nice to know about transactions: that they've locked all the tables they're going to lock. That would be sufficient but overly strong test. It's possible to know that if other tables are accessed they'll be with a brand new snapshot.
