Turns out the big culprit was actually not the database...

prefect_server=# \l+
                                                                    List of databases
      Name      |  Owner  | Encoding |  Collate   |   Ctype    |  Access privileges  |  Size   | Tablespace |                Description
----------------+---------+----------+------------+------------+---------------------+---------+------------+--------------------------------------------
 postgres       | prefect | UTF8     | en_US.utf8 | en_US.utf8 |                     | 7521 kB | pg_default | default administrative connection database
 prefect_server | prefect | UTF8     | en_US.utf8 | en_US.utf8 |                     | 1083 MB | pg_default |
 template0      | prefect | UTF8     | en_US.utf8 | en_US.utf8 | =c/prefect         +| 7521 kB | pg_default | unmodifiable empty database
                |         |          |            |            | prefect=CTc/prefect |         |            |
 template1      | prefect | UTF8     | en_US.utf8 | en_US.utf8 | =c/prefect         +| 7521 kB | pg_default | default template for new databases
                |         |          |            |            | prefect=CTc/prefect |         |            |
(4 rows)

prefect@data-integration:~$ df
Filesystem     1K-blocks    Used Available Use% Mounted on
udev             1012520       0   1012520   0% /dev
tmpfs             204360   21236    183124  11% /run
/dev/sda1       10126600 9379576    212908  98% /
tmpfs            1021796      16   1021780   1% /dev/shm
tmpfs               5120       0      5120   0% /run/lock
tmpfs            1021796       0   1021796   0% /sys/fs/cgroup
/dev/sda15        126710    6148    120562   5% /boot/efi
overlay         10126600 9379576    212908  98% /var/lib/docker/overlay2/76286bab1d42d570a9adc9b810d88bc21e63b4d325447af9bdb75a930d08a20e/merged
overlay         10126600 9379576    212908  98% /var/lib/docker/overlay2/6c70c2215f12f1fed0c2ff9a7eabff0a1834816e135c56cd63b1c1a6fe9becb3/merged
overlay         10126600 9379576    212908  98% /var/lib/docker/overlay2/0ca7b9d98a8d87f2ab76a0e34211f93110b26ce23efcd533517fb8b2d6b0f362/merged
overlay         10126600 9379576    212908  98% /var/lib/docker/overlay2/e64581578f1140a39de54d4dc9e3999b9d928804a06a5538210867dce87d7e8b/merged
overlay         10126600 9379576    212908  98% /var/lib/docker/overlay2/7a7aa1e9979ddd4ba92afae315895bb3a7bf4000fcc9dbfcabc08c8fe064a4f5/merged
overlay         10126600 9379576    212908  98% /var/lib/docker/overlay2/51be48a363e4f01bee5ca8b0bfb1868caa06ef0eb50f7f5b9023d817e909b7c4/merged
tmpfs             204356       0    204356   0% /run/user/1001

I haven't really figured this out yet. Will update here with my findings.

Okay I'm finding multiple sources of files piling up. Is it safe to delete old files in

.prefect/results

manually? (I'm using LocalAgent with defaults, and no result caching and not making use of checkpointing)