Обсуждение: Saw some strange behavior when using `INSERT ON CONFLICT` inside a transaction.

Repro steps:
* I created the table:

```

create table t (col TEXT primary key);

```

* Open two database consoles and use the following queries in them:

```

1 begin;
2 select txid_current();
3 insert into t (col) values ('test') on conflict (col) do nothing;
4 commit;

```

I ran 1 and 2 in both. It worked for both.
And then I ran query 3 in the first console. It worked.
After that I ran query 3 in the second console. It got stuck!
When I commit the tx in first console, the stuck query in second console finishes
The transaction isolation level is 'read committed'. 

This is absolutely as it should be. 

When you issue the statement 3 in the second transaction it cannot know if the first transaction will be committed, rollbacked or aborted. If the first transaction commits, then there will be a conflict on the insertion in the  second xaction and it should do nothing, so this statement will not insert anything and return successfully, then the commit should work as well. But if the first transaction aborts or rollbacks, then the insert on the 2nd xaction should be attempted and most probably succeed. That's why the second xaction blocks. You can view the locks as you experiment via the pg_locks view.

--

Best Regards
Sagar Tiwari

On Sat, Aug 30, 2025 at 01:13:35PM +0530, Sagar Tiwari wrote:
> Repro steps:
> * I created the table:
> ```
> create table t (col TEXT primary key);
> ```
> 
> * Open two database consoles and use the following queries in them:
> 
> ```
> 1 begin;
> 2 select txid_current();
> 3 insert into t (col) values ('test') on conflict (col) do nothing;
> 4 commit;
> ```
> 
> I ran 1 and 2 in both. It worked for both.
> And then I ran query 3 in the first console. It worked.
> After that I ran query 3 in the second console. It got stuck!
> When I commit the tx in first console, the stuck query in second console
> finishes
> The transaction isolation level is 'read committed'.

The transaction that loses the race to do the insert (step 3) has to
block somewhere waiting for the winning transaction to commit or
rollback.  The losing transaction could have continued speculatively and
block in the commit (step 4) instead of in the insert, but it still had
to block.

Does it matter that it blocks in the insert instead of the commit?