Date: Thu, 10 Apr 2025 13:18:15 +0200
From: hubert depesz lubaczewski <depesz@depesz.com>
Sender: depesz@depesz.com
To: gweatherby@uchc.edu, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18886: identity duplicate key
Message-ID: <Z_eo980Ge03avLno@depesz.com>
Reply-To: depesz@depesz.com
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On Wed, Apr 09, 2025 at 11:04:20PM +0000, PG Bug reporting form wrote:
> The following bug has been logged on the website:
> 
> Bug reference:      18886
> Logged by:          Gerard Weatherby
> Email address:      gweatherby@uchc.edu
> PostgreSQL version: 17.2
> Operating system:   Ubuntu 24
> Description:        
> 
> I observed this:
> 
> registry=#  SELECT last_value, is_called FROM performance.vm_load_id_seq;
>  last_value | is_called 
> ------------+-----------
>    12935994 | t
> (1 row)
> 
> registry=# \d performance.vm_load
>                                 Table "performance.vm_load"
>   Column   |           Type           | Collation | Nullable |          
> Default        
> -----------+--------------------------+-----------+----------+------------------------------
>  id        | integer                  |           | not null | generated
> always as identity
>  vm_id     | integer                  |           | not null |  
>  load15    | double precision         |           | not null |  
>  idle      | double precision         |           | not null |  
>  stat_time | timestamp with time zone |           | not null |  
> Indexes:
>     "vm_load_pk" PRIMARY KEY, btree (id)
>     "vm_load_id_vm_id_stat_time_index" btree (id, vm_id, stat_time)
>     "vm_load_stat_time_index" btree (stat_time)
> Foreign-key constraints:
>     "vm_load_virtual_machines_id_fk" FOREIGN KEY (vm_id) REFERENCES
> performance.virtual_machines(id) ON UPDATE RESTRICT ON DELETE RESTRICT
> 
> registry=# INSERT INTO performance.vm_load(vm_id,load15,idle,stat_time)
> values(437,0.0,94.31128026560856,'2025-04-09T22:25:26.326639+00:00'::timestamptz)
> ;
> ERROR:  duplicate key value violates unique constraint "vm_load_pk"
> DETAIL:  Key (id)=(1314208) already exists. 
> 
> Unable to figure out what was going on, I did this, and it seemed to fix the
> issue:

You must have inserted some rows specifying value for id column. In such
case identity/sequence is not updated, so afterwards you will get
duplicate errors, as sequence returns (as new/next) value that already
exists in table.

Solution:

select setval('performance.vm_load_id_seq'::regclass, max(id) + 1 ) from performance.vm_load;

and find whatever was doing these inserts, and fix it.

Also, please note that this mailing list for reporting bugs in
PostgreSQL, and your situation doesn't qualify as such. It's simple
operator/programmer error.

Best regards,

depesz