From: Masahiko Sawada [mailto:sawada.m...@gmail.com] > On Thu, Jan 25, 2018 at 3:14 PM, Tsunakawa, Takayuki > <tsunakawa.ta...@jp.fujitsu.com> wrote: > > * Why does autovacuum launcher always choose only one database when that > database need vacuuming for XID wraparound? Shouldn't it also choose other > databases? > > Yeah, I'd also like to fix this issue. This can be problem even in other > case; there are two databases that require anti-wraparound vacuum, and one > of them has a very large table that could take a long time to vacuum. In > this case, if autovacuum chooses the database having big table first, > another database would not be selected until an autovacuum worker completes > vacuum on the large table. To deal with it, I think we can make autovacuum > workers tell that it is no longer necessary to launch a new autovacuum worker > on the database to autovacuum launcher before exit. For example, autovacuum > worker reports both the total number of relations and the number of relations > that require an anti-wraparound vacuum to the stats collector.
Thanks for commenting. I believe you have deep knowledge and experience with vacuum because you did a great work for freeze map in 9.6, so I appreciate your help! How would you use those two counts? How about just modifying do_start_worker(), so that the launcher chooses a database in the following order? 1. wraparound-risky database not being vacuumed by any worker 2. non-wraparound-risky database not being vacuumed by any worker 3. wraparound-risky database being vacuumed by any worker 4. non-wraparound-risky database being vacuumed by any worker Regards Takayuki Tsunakawa
