Why does vacuum full wait after it is "done"?

I am running a vacuum on a very large table.

When I run it, it says:

bacula=# VACUUM FULL VERBOSE file_partition_19
bacula-# ;
INFO:  vacuuming "public.file_partition_19"
INFO:  "file_partition_19": found 16242451 removable, 21024161 nonremovable row versions in 900380 pages
DETAIL:  0 dead row versions cannot be removed yet.
CPU 5.14s/14.42u sec elapsed 19.61 sec.
VACUUM
Time: 163784.767 ms
bacula=# 

When it does this, it shows up to the CPU line fairly quickly, then waits a long time before it shows the final two lines (+ the prompt). This is reflected in the difference in time - "elapsed 19.61 sec", compared to to the "Time:" of 163 seconds (shown because I set \timing on).

虽然我还没有计时,但两次都是正确的 - 启动命令,等待20秒,然后显示"CPU"行,然后等待大约3分钟,然后打印其余部分.

这是正常的吗？为什么会这样？