PostgreSQL 문서에는 SELECT를 포함한 모든 SQL이 트랜잭션 (BEGIN ~ COMMIT) 내에서 실행된다고 하네요

PostgreSQL actually treats every SQL statement as being executed within a transaction. If you do not issue a BEGIN command, then each individual statement has an implicit BEGIN and (if successful) COMMIT wrapped around it. A group of statements surrounded by BEGIN and COMMIT is sometimes called a transaction block.

https://www.postgresql.org/docs/13/tutorial-transactions.html

pg_stat_database에서 xact_commit 값을 참고하시면 좋을 듯 합니다.

postgres=# select xact_commit from pg_stat_database where datname='postgres'
postgres-# ;
 xact_commit
-------------
      850753
(1 row)

postgres=# select xact_commit from pg_stat_database where datname='postgres'
;
 xact_commit
-------------
      850754
(1 row)