Jobs: completed_time is truncated to the second, so it can precede reserved_time #1600

Summary

The jobs table declares reserved_time and completed_time as datetime(3) (jobs.py:167-168). reserve() writes reserved_time as CURRENT_TIMESTAMP(3) (jobs.py:464), but complete() and error() take completed_time from SELECT CURRENT_TIMESTAMP (jobs.py:499, 529), which has no fractional seconds. MySQL truncates it to the whole second, so any job that finishes in the second it was reserved records a completed_time earlier than its reserved_time.

Error records carry no duration, so completed_time - reserved_time is the only measure of how long a failed job ran, and it comes out negative or up to a second short. With keep_completed = True, success records show the same inversion.

Reproduction

DataJoint 2.3.5.dev8 (master, a00b89f), MySQL 8.0.46, Python 3.11:

import time
import datajoint as dj

dj.config.jobs.keep_completed = True
schema = dj.Schema("scratch_job_times")

@schema
class Item(dj.Manual):
    definition = """
    item : int32
    """

@schema
class Result(dj.Computed):
    definition = """
    -> Item
    ---
    value : int32
    """

    def make(self, key):
        time.sleep(0.2)
        self.insert1(dict(key, value=key["item"]))

Item.insert({"item": i} for i in range(5))
Result.populate(reserve_jobs=True)
for job in Result.jobs.to_dicts(order_by="item"):
    flag = "  <- completed before reserved" if job["completed_time"] < job["reserved_time"] else ""
    print(job["item"], job["reserved_time"], job["completed_time"], flag)

Output:

0 2026-10-17 21:37:31.124000 2026-10-17 21:37:31   <- completed before reserved
1 2026-10-17 21:37:31.335000 2026-10-17 21:37:31   <- completed before reserved
2 2026-10-17 21:37:31.546000 2026-10-17 21:37:31   <- completed before reserved
3 2026-10-17 21:37:31.754000 2026-10-17 21:37:31   <- completed before reserved
4 2026-10-17 21:37:31.966000 2026-10-17 21:37:32

Expected behavior

completed_time is recorded at the column's declared precision and on the same clock as reserved_time, so completed_time >= reserved_time always holds: SELECT CURRENT_TIMESTAMP(3) in complete() and error(). On PostgreSQL, CURRENT_TIMESTAMP is the start of the transaction rather than the statement; the statement-time adapter expression proposed in #1584 would serve here too.