Message-ID: <gh-pgjdbc-pgjdbc-3906@github.com>
From: "atorik (@atorik)" <noreply+atorik@github.com>
To: "pgjdbc/pgjdbc" <noreply+pgjdbc-pgjdbc@github.com>
Date: Mon, 12 Jan 2026 05:30:54 +0000
Subject: [pgjdbc/pgjdbc] PR #3906: fix:  incorrect pg_stat_replication.reply_time calculation
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X-GitHub-Issue: 3906
X-GitHub-Repo: pgjdbc/pgjdbc
X-GitHub-State: merged
X-GitHub-Type: pull_request
X-GitHub-Url: https://github.com/pgjdbc/pgjdbc/pull/3906
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Hi,

When creating a replication connection using the PostgreSQL JDBC driver,
`pg_stat_replication.reply_time` is reported as a timestamp more than 20 years in the past.

Example:

```
=# select application_name, reply_time from pg_stat_replication;
    application_name    |          reply_time
------------------------+-------------------------------
 PostgreSQL JDBC Driver | 1999-12-21 10:01:58.904961+09
(1 row)
```

I initially noticed this issue while using Debezium, but it can also be reproduced with a minimal replication connection app like [this](https://github.com/user-attachments/files/24557645/LogicaldecodingTest.java).

`reply_time` was calculated using `System.nanoTime()`, which is only suitable for measuring elapsed time and not wall-clock time. Additionally, `TimeUnit.convert()` was used with an incorrect source unit.

This change addresses the issue by:

- Replacing `System.nanoTime()` with `System.currentTimeMillis()` to obtain a proper wall-clock timestamp.
- Correcting the `TimeUnit.convert()` usage so that the source unit matches the actual time value being converted.

What do you think?

### All Submissions:

* [x]  Have you followed the guidelines in our [Contributing](https://github.com/pgjdbc/pgjdbc/blob/master/CONTRIBUTING.md) document?
* [x]  Have you checked to ensure there aren't other open [Pull Requests](../../pulls) for the same update/change?

### Changes to Existing Features:

* [x] Does this break existing behaviour? If so please explain.
* [x] Have you added an explanation of what your changes do and why you'd like us to include them?
* [x] Have you written new tests for your core changes, as applicable?
  * No new tests have been added at this time. I considered adding a test that verifies `reply_time` is not excessively in the past (e.g., more than 24 hours earlier than the current time). However, I'm not sure it's worth adding. 
* [x] Have you successfully run tests with your changes locally?