From: Chao Li <li.evan.chao@gmail.com>
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Subject: Fix a server crash problem from pg_get_database_ddl
Message-Id: <573E45C1-31A4-4885-A00C-1A2171159A2A@gmail.com>
Date: Wed, 15 Apr 2026 13:51:31 +0800
To: Postgres hackers <pgsql-hackers@lists.postgresql.org>
Archived-At: 
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Hi,

While doing some testing, I hit a server crash:
```
2026-04-15 11:30:17.377 CST [98179] LOG:  client backend (PID 41260) was =
terminated by signal 11: Segmentation fault: 11
2026-04-15 11:30:17.377 CST [98179] DETAIL:  Failed process was running: =
SELECT * FROM pg_get_database_ddl('db1'::regdatabase);
2026-04-15 11:30:17.377 CST [98179] LOG:  terminating any other active =
server processes
2026-04-15 11:30:17.380 CST [44361] FATAL:  the database system is in =
recovery mode
```

After debugging it, I found that the crash happened because I had =
mistakenly deleted the tablespace entry directly from pg_tablespace, and =
pg_get_database_ddl_internal() calls get_tablespace_name() without =
checking whether the return value is NULL.

So this doesn't seem like a bug a normal user could hit. It is more like =
a superuser-only mistake that creates an invalid catalog state. I think =
that even in such an edge case, we should raise a proper error instead =
of crashing the backend.

BTW, I have verified that in this case, ALTER DATABASE ... SET =
TABLESPACE can move the database to a valid tablespace and recover from =
the issue.

This patch fixes that by checking for a NULL result and throwing an =
error.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/


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