Re: autovacuum next steps

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). In general the only time it's a
good idea to have multiple vacuums running at the same time is when a
big table is starving a small hot table and causing bloat.

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.

Thoughts?