TRUNCATE ONLY with foreign keys and triggers disabled
Hello list,
While doing TRUNCATE ONLY I get:
ERROR: cannot truncate a table referenced in a foreign key constraint
But in my case the table to be truncated is already empty, and the
TRIGGERS are disabled in all tables.
I wonder, is there a deeper reason for this error, or is it just an
implementation shortcoming? In other words, how easy would it be to write
a patch that allows TRUNCATE even with foreign keys when triggers are
disabled or the table is empty?
Thanks in advance,
Dimitris
Dimitrios Apostolou <jimis@gmx.net> writes:
While doing TRUNCATE ONLY I get:
ERROR: cannot truncate a table referenced in a foreign key constraint
But in my case the table to be truncated is already empty, and the
TRIGGERS are disabled in all tables.
IIRC, it will let you do it if you truncate both the referenced and
referencing tables in the same command. The state of the triggers
is not material to this, since TRUNCATE doesn't fire them anyway.
regards, tom lane
On Mon, 14 Apr 2025, Tom Lane wrote:
Dimitrios Apostolou <jimis@gmx.net> writes:
While doing TRUNCATE ONLY I get:
ERROR: cannot truncate a table referenced in a foreign key constraint
But in my case the table to be truncated is already empty, and the
TRIGGERS are disabled in all tables.IIRC, it will let you do it if you truncate both the referenced and
referencing tables in the same command. The state of the triggers
is not material to this, since TRUNCATE doesn't fire them anyway.
Thanks Tom, however that is not possible in my case, the referenced table
is possibly just populated and potentially very big (partitioned table
with many sub-partitions).
Context is that I've modified pg_restore to accept --data-only --clean,
and issues a TRUNCATE ONLY before each table's COPY, in the same
transaction (thus avoiding WAL too). Will send an RFC patch to
pgsql-hackers when I verify it works.
Dimitris
On Mon, 14 Apr 2025, Dimitrios Apostolou wrote:
On Mon, 14 Apr 2025, Tom Lane wrote:
Dimitrios Apostolou <jimis@gmx.net> writes:
While doing TRUNCATE ONLY I get:
ERROR: cannot truncate a table referenced in a foreign key constraint
But in my case the table to be truncated is already empty, and the
TRIGGERS are disabled in all tables.IIRC, it will let you do it if you truncate both the referenced and
referencing tables in the same command. The state of the triggers
is not material to this, since TRUNCATE doesn't fire them anyway.Thanks Tom, however that is not possible in my case, the referenced table is
possibly just populated and potentially very big (partitioned table with many
sub-partitions).
Terminology correction: I meant the *referencing* table has just been
populated. I'm trying to delete the *referenced* table and I get the
error.
Dimitris
On Mon, 2025-04-14 at 17:05 +0200, Dimitrios Apostolou wrote:
I meant the *referencing* table has just been
populated. I'm trying to delete the *referenced* table and I get the
error.
That would break the foreign key constraint, right?
PostgreSQL cannot allow that.
Yours,
Laurenz Albe
On 4/14/25 08:07, Laurenz Albe wrote:
On Mon, 2025-04-14 at 17:05 +0200, Dimitrios Apostolou wrote:
I meant the *referencing* table has just been
populated. I'm trying to delete the *referenced* table and I get the
error.That would break the foreign key constraint, right?
PostgreSQL cannot allow that.
I believe the OP is disabling all triggers including system ones if I
follow correctly and possibly running a foul of;
https://www.postgresql.org/docs/current/sql-altertable.html
" Disabling or enabling internally generated constraint triggers
requires superuser privileges; it should be done with caution since of
course the integrity of the constraint cannot be guaranteed if the
triggers are not executed."
Yours,
Laurenz Albe
--
Adrian Klaver
adrian.klaver@aklaver.com
On Mon, 14 Apr 2025, Adrian Klaver wrote:
On 4/14/25 08:07, Laurenz Albe wrote:
On Mon, 2025-04-14 at 17:05 +0200, Dimitrios Apostolou wrote:
I meant the *referencing* table has just been
populated. I'm trying to delete the *referenced* table and I get the
error.That would break the foreign key constraint, right?
PostgreSQL cannot allow that.I believe the OP is disabling all triggers including system ones if I follow
correctly and possibly running a foul of;https://www.postgresql.org/docs/current/sql-altertable.html
" Disabling or enabling internally generated constraint triggers requires
superuser privileges; it should be done with caution since of course the
integrity of the constraint cannot be guaranteed if the triggers are not
executed."
Exactly that. I learned this from pg_restore --disable-triggers, as a way
to speed-up insertion.
Since triggers are disabled, I assumed that postgresql shouldn't care
about referential integrity in TRUNCATE.
Dimitris
On 4/14/25 08:20, Dimitrios Apostolou wrote:
On Mon, 14 Apr 2025, Adrian Klaver wrote:
On 4/14/25 08:07, Laurenz Albe wrote:
On Mon, 2025-04-14 at 17:05 +0200, Dimitrios Apostolou wrote:
I meant the *referencing* table has just been
populated. I'm trying to delete the *referenced* table and I get the
error.That would break the foreign key constraint, right?
PostgreSQL cannot allow that.I believe the OP is disabling all triggers including system ones if I
follow
correctly and possibly running a foul of;https://www.postgresql.org/docs/current/sql-altertable.html
" Disabling or enabling internally generated constraint triggers requires
superuser privileges; it should be done with caution since of course the
integrity of the constraint cannot be guaranteed if the triggers are not
executed."Exactly that. I learned this from pg_restore --disable-triggers, as a way
to speed-up insertion.Since triggers are disabled, I assumed that postgresql shouldn't care
about referential integrity in TRUNCATE.
I'm going to say the depends on order of execution. Without seeing the
code changes you have done there is really no way to determine what the
exact issue is.
Dimitris
--
Adrian Klaver
adrian.klaver@aklaver.com
On Mon, 14 Apr 2025, Adrian Klaver wrote:
On 4/14/25 08:20, Dimitrios Apostolou wrote:
On Mon, 14 Apr 2025, Adrian Klaver wrote:
On 4/14/25 08:07, Laurenz Albe wrote:
On Mon, 2025-04-14 at 17:05 +0200, Dimitrios Apostolou wrote:
I meant the *referencing* table has just been
populated. I'm trying to delete the *referenced* table and I get the
error.That would break the foreign key constraint, right?
PostgreSQL cannot allow that.I believe the OP is disabling all triggers including system ones if I
follow
correctly and possibly running a foul of;https://www.postgresql.org/docs/current/sql-altertable.html
" Disabling or enabling internally generated constraint triggers requires
superuser privileges; it should be done with caution since of course the
integrity of the constraint cannot be guaranteed if the triggers are not
executed."Exactly that. I learned this from pg_restore --disable-triggers, as a way
to speed-up insertion.Since triggers are disabled, I assumed that postgresql shouldn't care
about referential integrity in TRUNCATE.I'm going to say the depends on order of execution. Without seeing the code
changes you have done there is really no way to determine what the exact
issue is.
Sent patch here:
/messages/by-id/4589087c-ec6f-4407-1f82-6cb2e681ac0a@gmx.net
The reason I first sent here (pgsql-general) is that I wondered if the
error is just an implementation shortcoming without deeper reasons, thus
it would be achievable to try to fix it myself.
Dimitris