Matthew T. O'Connor wrote: > Alvaro Herrera wrote: > >After staring at my previous notes for autovac scheduling, it has become > >clear that this basics of it is not really going to work as specified. > >So here is a more realistic plan: > > [Snip Detailed Description] > > >How does this sound? > > On first blush, I'm not sure I like this as it doesn't directly attack > the table starvation problem, and I think it could be a net loss of speed. > > VACUUM is I/O bound, as such, just sending multiple vacuum commands at a > DB isn't going to make things faster, you are now going to have multiple > processes reading from multiple tables at the same time. I think in > general this is a bad thing (unless we someday account for I/O made > available from multiple tablespaces).
Yeah, I understand that. However, I think that can be remedied by using a reasonable autovacuum_vacuum_cost_delay setting, so that each worker uses less than the total I/O available. The main point of the proposal is to allow multiple workers on a DB while also allowing multiple databases to be processed in parallel. > I think we can extend the current autovacuum stats to add one more > column that specifies "is hot" or something to that effect. Then when > the AV launcher sends a worker to a DB, it will first look for tables > marked as hot and work on them. While working on hot tables, the > launcher need not send any additional workers to this database, if the > launcher notices that a worker is working on regular tables, it can send > another worker which will look for hot tables to working, if the worker > doesn't find any hot tables that need work, then it exits leaving the > original working to continue plodding along. How would you define what's a "hot" table? -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
