backend_start何以比xact_start伟大

Question

backend_start怎么能大于xact_start/query_start的2天？第三次会议看上去不错，但前两次看起来很奇怪，这有可能吗？这意味着什么吗？

pg=> select * from pg_catalog.pg_stat_activity where usename = 'etl_user' and state = 'active' and backend_xmin = 65201266;              
datid | datname |  pid  |usesysid | usename  |    application_name    |  client_addr   | client_hostname | client_port |         backend_start         |          xact_start           |         query_start          |         state_change          | wait_event_type | wait_event| state  | backend_xid | backend_xmin |                                                                                                    query                          |  backend_type
-------+---------+-------+----------+----------+------------------------+----------------+-----------------+-------------+-------------------------------+-------------------------------+-------------------------------+-------------------------------+-----------------+------------+--------+-------------+--------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------
 16408 | pg| 37908 |   229661 | etl_user | PostgreSQL JDBC Driver |                |                 |             | 2021-04-20 21:36:22.540271+00 | 2021-04-17 22:31:32.314106+00 | 2021-04-17 22:31:32.317577+00 | 2021-04-20 21:36:22.541472+00 |                 || active |             |     65201266 | SELECT 1 FROM (SELECT ...)  | parallel worker
 16408 | pg| 37909 |   229661 | etl_user | PostgreSQL JDBC Driver |                |                 |             | 2021-04-20 21:36:22.540909+00 | 2021-04-17 22:31:32.314106+00 | 2021-04-17 22:31:32.317577+00 | 2021-04-20 21:36:22.542134+00 |                 || active |             |     65201266 | SELECT 1 FROM (SELECT ...)  | parallel worker
 16408 | pg|  3601 |   229661 | etl_user | PostgreSQL JDBC Driver | 10.175.130.142 |                 |       49832 | 2021-04-17 22:31:32.232008+00 | 2021-04-17 22:31:32.314106+00 | 2021-04-17 22:31:32.317577+00 | 2021-04-17 22:31:32.317578+00 |                 || active |             |     65201266 | SELECT 1 FROM (SELECT ...)  | client backend
(3 rows)

Answer 1

在我看来，这些都是为帮助领导者而成立的并行工作者，他们继承了领导者xact_start，而不是backend_start。它将有助于查看pg_stat_activity中的其余列，并了解其版本。

Answer 2

是的，那看起来不可能。

我唯一的解释是，自会话开始以来，有人更改了系统时间。