Re: autovacuum worker started without a worker entry

Hi all,
I occasionally see the message "WARNING:  autovacuum worker started
without a worker entry" in the logs.
From what I can see here
<https://github.com/postgres/postgres/blob/master/src/backend/postmaster/autovacuum.c#L1678>,
the launcher forked a worker and in the meantime the launcher decided
the worker is no more useful. If that is right, I'm guessing why the
worker should not be useful anymore: since a single worker could work
on a table, the only reason I can find is that someone run manually
vacuum within that database/table.

Moreover, I've a question about emergency autovacuum (wraparound).
Since autovacuum workers are started by postmaster on a signal
received by the autovacuum launcher, and since with autovacuum = off
the latter is not running, how does the postmaster decide to start and
emergency autovacuum?
I only found what seems to me a normal autovacuum start at
<https://github.com/postgres/postgres/blob/master/src/backend/postmaster/postmaster.c#L5263>.

I think, this block when it is about to assign the next xid, it does the math, and triggers an autolauncher start.

I might be wrong, I did not run a backtrace though :)

 * Check to see if it's safe to assign another XID. This protects against
 * catastrophic data loss due to XID wraparound. The basic rules are:
 * If we're past xidVacLimit, start trying to force autovacuum cycles.
 * If we're past xidWarnLimit, start issuing warnings.
 * If we're past xidStopLimit, refuse to execute transactions, unless
 * we are running in single-user mode (which gives an escape hatch
 * to the DBA who somehow got past the earlier defenses).