BUG #17434: CREATE/DROP DATABASE can be executed in the same transaction with other commands

The following bug has been logged on the website:

Bug reference:      17434
Logged by:          Yugo Nagata
Email address:      nagata@sraoss.co.jp
PostgreSQL version: 14.2
Operating system:   Ubuntu
Description:

CREATE/DROP DATABASE can be executed in the same transaction with other
commands when we use pipeline mode in pgbench or libpq API. If the
transaction aborts, this causes an inconsistency between the system catalog
and base directory.

Here is an example using the pgbench /startpipeline meta command.

----------------------------------------------------
(1)  Confirm that there are four databases from psql and directories in
base.

$ psql -l
                                 List of databases
   Name    | Owner  | Encoding |   Collate   |    Ctype    |   Access
privileges   
-----------+--------+----------+-------------+-------------+-----------------------
 postgres  | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
 template0 | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/"yugo-n"
     +
           |        |          |             |             |
"yugo-n"=CTc/"yugo-n"
 template1 | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/"yugo-n"
     +
           |        |          |             |             |
"yugo-n"=CTc/"yugo-n"
 test0     | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
(4 rows)

$ ls data/base/
1  13014  13015  16409  pgsql_tmp

(2) Execute CREATE DATABASE in a transaction, and the transaction fails.

$ cat pipeline_createdb.sql 
\startpipeline
create database test;
select 1/0;
\endpipeline

$ pgbench -t 1 -f pipeline_createdb.sql -M extended
pgbench (14.2)
starting vacuum...end.
pgbench: error: client 0 script 0 aborted in command 3 query 0: 
....

(3) There are still four databases but a new directory was created in
base.

$ psql -l
                                 List of databases
   Name    | Owner  | Encoding |   Collate   |    Ctype    |   Access
privileges   
-----------+--------+----------+-------------+-------------+-----------------------
 postgres  | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
 template0 | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/"yugo-n"
     +
           |        |          |             |             |
"yugo-n"=CTc/"yugo-n"
 template1 | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/"yugo-n"
     +
           |        |          |             |             |
"yugo-n"=CTc/"yugo-n"
 test0     | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
(4 rows)

$ ls data/base/
1  13014  13015  16409  16411  pgsql_tmp

(4) Next, execute DROP DATABASE in a transaction, and the transaction
fails.

$ cat pipeline_dropdb.sql 
\startpipeline
drop database test0;
select 1/0;
\endpipeline

$ pgbench -t 1 -f pipeline_dropdb.sql -M extended
pgbench (14.2)
starting vacuum...end.
pgbench: error: client 0 script 0 aborted in command 3 query 0:
...

(5) There are still four databases but the corresponding directory was
deleted in base.

$ psql -l
                                 List of databases
   Name    | Owner  | Encoding |   Collate   |    Ctype    |   Access
privileges   
-----------+--------+----------+-------------+-------------+-----------------------
 postgres  | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
 template0 | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/"yugo-n"
     +
           |        |          |             |             |
"yugo-n"=CTc/"yugo-n"
 template1 | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | =c/"yugo-n"
     +
           |        |          |             |             |
"yugo-n"=CTc/"yugo-n"
 test0     | yugo-n | UTF8     | ja_JP.UTF-8 | ja_JP.UTF-8 | 
(4 rows)

$ ls data/base/
1  13014  13015  16411  pgsql_tmp

(6) We cannot connect the database "test0".

$ psql test0
psql: error: connection to server on socket "/tmp/.s.PGSQL.25435" failed:
FATAL:  database "test0" does not exist
DETAIL:  The database subdirectory "base/16409" is missing.
----------------------------------------------------

Detailed discussions are here;
https://www.postgresql.org/message-id/20220301151704.76adaaefa8ed5d6c12ac3079@sraoss.co.jp