AccessExclusive lock origin - postgresql

Question

I am running the following query in first transaction:
BEGIN ISOLATION LEVEL repeatable read;
SELECT balance from "Users" WHERE id = 1 FOR UPDATE;
UPDATE "Users" SET "balance"="balance"+1 WHERE id = 1;
Then the second, from different connection which is exactly same. On SELECT ... FOR UPDATE it's waiting.
Then I run the following to see the locks
select t.relname,l.locktype,l.tuple,page,virtualtransaction,pid,mode,granted from pg_locks l, pg_stat_all_tables t where l.relation=t.relid order by relation asc;
It shows row locks (ROW SHARE, ROW EXCLUSIVE), which is fine. But I also see
Users tuple 9 0 11/17085 199957 AccessExclusiveLock TRUE
According to documentation AccessExclusiveLock comes from:
Acquired by the ALTER TABLE, DROP TABLE, TRUNCATE, REINDEX, CLUSTER,
and VACUUM FULL commands. This is also the default lock mode for LOCK
TABLE statements that do not specify a mode explicitly.
I am not explicitly doing any of them and I can't find in docs how implicitly this lock is acquired. Moreover, what means tuple lock type and 9?
update #1:
I used the following query to get more info:
SELECT a.datname,
l.relation::regclass,
l.transactionid,
l.mode,
l.GRANTED,
a.usename,
a.query,
a.query_start,
age(now(), a.query_start) AS "age",
a.pid
FROM pg_stat_activity a
JOIN pg_locks l ON l.pid = a.pid
ORDER BY a.query_start;
So indeed database is same, query is the one that is blocked.
mydb "Users" AccessExclusiveLock TRUE appuserdev SELECT balance from "Users" WHERE id = 1 for update; 2021-08-30 08:06:38.864007+00 00:08:06.978082 205464

Answer 1

The docs you are reading apply to AccessExclusiveLock on tables. But what you are seeing is not a table lock. I don't think the lock modes for non-tables are explicitly documented anywhere, but you can generally figure it out through analogy.
On the other hand, I also don't see what you see. I see an ExclusiveLock, not an AccessExclusiveLock, being held on the tuple.