question on audit columns

Hi,

In your scenario, triggers can add some overhead since they require extra
processing after each update operation. Considering the size of your table
and the high transaction volume, you need to observe that this might
significantly affect performance.

On Wed, 4 Sept 2024 at 17:50, yudhi s <learnerdatabase99@gmail.com> wrote:

On Wed, Sep 4, 2024 at 6:29 PM Muhammad Usman Khan <usman.k@bitnine.net>
wrote:

Hi,

In your scenario, triggers can add some overhead since they require extra
processing after each update operation. Considering the size of your table
and the high transaction volume, you need to observe that this might
significantly affect performance.

On Wed, 4 Sept 2024 at 17:50, yudhi s <learnerdatabase99@gmail.com> wrote:

Hello,
In postgres database , we have all the tables with audit columns like
created_by_user, created_timestamp,updated_by_user, updated_timestamp. So
we have these fields that were supposed to be populated by the time at
which the insert/update operation happened on the database but not at the
application level. So we are planning to populate the created_by_user,
created_timestamp columns by setting a default value of "current_timestamp"
and "current_user" for the two columns, but no such this is available to
populate while we do the update of the row, so the only option seems to be
through a trigger.

So wanted to check with the experts here ,considering the table will be
DML heavy table (300M+ transactions will be inserted daily), Is is okay to
have the trigger for this table for populating all the audit columns or
should we keep default for created_by_user, created_timestamp and just
trigger for the update related two audit column? Basically wanted to see,
if the default value does the same thing as a trigger or it does something
more optimally than trigger?

Regards
Yudhi

Thank you so much. So do you mean to say that , we should add default
values for the create_timestamp and create_user_id as current_timestamp and
current_user, but for update_user_id and update_timestamp , we can ask the
application to update the values manually , whenever they are executing the
update statement on the rows?

Yes this would be the better approach.

Sent from Outlook for Android<https://aka.ms/AAb9ysg&gt;
________________________________
From: yudhi s <learnerdatabase99@gmail.com>
Sent: Wednesday, September 4, 2024 6:10:04 PM
To: Muhammad Usman Khan <usman.k@bitnine.net>
Cc: pgsql-general <pgsql-general@lists.postgresql.org>
Subject: Re: question on audit columns

On Wed, Sep 4, 2024 at 6:29 PM Muhammad Usman Khan <usman.k@bitnine.net<mailto:usman.k@bitnine.net>> wrote:
Hi,

In your scenario, triggers can add some overhead since they require extra processing after each update operation. Considering the size of your table and the high transaction volume, you need to observe that this might significantly affect performance.

On Wed, 4 Sept 2024 at 17:50, yudhi s <learnerdatabase99@gmail.com<mailto:learnerdatabase99@gmail.com>> wrote:
Hello,
In postgres database , we have all the tables with audit columns like created_by_user, created_timestamp,updated_by_user, updated_timestamp. So we have these fields that were supposed to be populated by the time at which the insert/update operation happened on the database but not at the application level. So we are planning to populate the created_by_user, created_timestamp columns by setting a default value of "current_timestamp" and "current_user" for the two columns, but no such this is available to populate while we do the update of the row, so the only option seems to be through a trigger.

So wanted to check with the experts here ,considering the table will be DML heavy table (300M+ transactions will be inserted daily), Is is okay to have the trigger for this table for populating all the audit columns or should we keep default for created_by_user, created_timestamp and just trigger for the update related two audit column? Basically wanted to see, if the default value does the same thing as a trigger or it does something more optimally than trigger?

Regards
Yudhi

Thank you so much. So do you mean to say that , we should add default values for the create_timestamp and create_user_id as current_timestamp and current_user, but for update_user_id and update_timestamp , we can ask the application to update the values manually , whenever they are executing the update statement on the rows?

On Wed, Sep 4, 2024 at 9:10 AM yudhi s <learnerdatabase99@gmail.com> wrote:

On Wed, Sep 4, 2024 at 6:29 PM Muhammad Usman Khan <usman.k@bitnine.net>
wrote:

Hi,

In your scenario, triggers can add some overhead since they require extra
processing after each update operation. Considering the size of your table
and the high transaction volume, you need to observe that this might
significantly affect performance.

On Wed, 4 Sept 2024 at 17:50, yudhi s <learnerdatabase99@gmail.com> wrote:

Hello,
In postgres database , we have all the tables with audit columns like
created_by_user, created_timestamp,updated_by_user, updated_timestamp. So
we have these fields that were supposed to be populated by the time at
which the insert/update operation happened on the database but not at the
application level. So we are planning to populate the created_by_user,
created_timestamp columns by setting a default value of "current_timestamp"
and "current_user" for the two columns, but no such this is available to
populate while we do the update of the row, so the only option seems to be
through a trigger.

So wanted to check with the experts here ,considering the table will be
DML heavy table (300M+ transactions will be inserted daily), Is is okay to
have the trigger for this table for populating all the audit columns or
should we keep default for created_by_user, created_timestamp and just
trigger for the update related two audit column? Basically wanted to see,
if the default value does the same thing as a trigger or it does something
more optimally than trigger?

Regards
Yudhi

Thank you so much. So do you mean to say that , we should add default
values for the create_timestamp and create_user_id as current_timestamp and
current_user,

That's the simplest way. But the application can overwrite those fields.

but for update_user_id and update_timestamp , we can ask the application
to update the values manually , whenever they are executing the update
statement on the rows?

How strict are the audit requirements?

If they're really strict, you might need INSERT and UPDATE triggers that
call security defined functions which write into a separate table not
accessible by the application. That table would have the application
table's PK, created_by_user, created_timestamp, updated_by_user and
updated_timestamp.

Would that table have a LOT of records? Sure.
Would it add overhead? Sure.

But the subsequently beefier hardware requirements and care in designing
the physical schema (for example, audit tables in a separate tablespace and
pg_wal/ on separate disk controllers, or a 10Gb SAN) are the price you pay
for strict audit requirements.

Of course, if the audit requirements are minimal, then sure, "default
values and the application" are Good Enough.

--
Death to America, and butter sauce.
Iraq lobster!

On 9/4/24 06:17, Khan Muhammad Usman wrote:

Yes this would be the better approach.

1) Except the overhead is now shifted to the application, which may or
not be better. You are also moving the audit responsibility to the
application and the application maintainers and making it application
specific. If a new application/client starts hitting the database and it
did not get the memo about the audit fields they won't be filled in.

2) I would recommend setting up a some realistic tests and see if the
overhead of the update triggers would be a concern.

--
Adrian Klaver
adrian.klaver@aklaver.com

On 9/4/24 06:17, Khan Muhammad Usman wrote:

Yes this would be the better approach.

1) Except the overhead is now shifted to the application, which may or
not be better. You are also moving the audit responsibility to the
application and the application maintainers and making it application
specific. If a new application/client starts hitting the database and it
did not get the memo about the audit fields they won't be filled in.

2) I would recommend setting up a some realistic tests and see if the
overhead of the update triggers would be a concern.

--
Adrian Klaver
adrian.klaver@aklaver.com

If it helps, we implemented a trigger based audit system 20 years ago. It both creates a separate inviolate audit table record and updates the record being changed with a timestamp and a userid of last change. We've not regretted it and moderate hardware deals well with the overhead (500+ table database, 80+ concurrent users, 18 million audit records a month).

--
Tim Clarke MSc, BSc (Hons), MBCS
IT Director
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On Wed, 4 Sep 2024 18:19:47 +0530
yudhi s <learnerdatabase99@gmail.com> wrote:

Hi,

In postgres database , we have all the tables with audit columns like
created_by_user, created_timestamp,updated_by_user, updated_timestamp. So
we have these fields that were supposed to be populated by the time at
which the insert/update operation happened on the database but not at the
application level. So we are planning to populate the created_by_user,
created_timestamp columns by setting a default value of "current_timestamp"
and "current_user" for the two columns, but no such this is available to
populate while we do the update of the row, so the only option seems to be
through a trigger.

If you can live with the fact that updated_by_user and updated_timestamp get the same values as created_by_user and created_timestamp when inserting the record, then you can do :

vv=> create table audit (created_by_user text default current_user, created_timestamp timestamp default now(), updated_by_user text default current_user, updated_timestamp timestamp default now(), data text);
CREATE TABLE
vv=> insert into audit (data) values ('abc');
INSERT 0 1
vv=> select * from audit;
created_by_user | created_timestamp | updated_by_user | updated_timestamp | data
-----------------+----------------------------+-----------------+----------------------------+------
vincent | 2024-09-05 19:17:53.446109 | vincent | 2024-09-05 19:17:53.446109 | abc
(1 row)

--as user postgres
update audit set updated_by_user = DEFAULT, updated_timestamp = DEFAULT, data = 'def';

vv=> select * from audit;
created_by_user | created_timestamp | updated_by_user | updated_timestamp | data
-----------------+----------------------------+-----------------+---------------------------+------
vincent | 2024-09-05 19:17:53.446109 | postgres | 2024-09-05 19:24:01.19186 | def
(1 row)

--
Bien à vous, Vincent Veyron

https://marica.fr/
Logiciel de suivi des contentieux juridiques, des sinistres d'assurance et des contrats

... and (3) the values are not updated on manual actions without
triggers - which might or might not be desirable depending on the intention.

Best,

Johannes

As far as the application being able to change those fields itself, you can
prevent that via column permissions, by leaving out the four audit columns
and doing something like:

GRANT INSERT (email, widget_count), UPDATE (email, widget_count) ON TABLE
foobar TO PUBLIC;

That way, inserts are guaranteed to use the default values of
current_timestamp() and current_user. And a BEFORE UPDATE trigger ensures
it changes the other two fields via the trigger function only.

Cheers,
Greg

P.S. Also check out https://www.pgaudit.org/ (PGAudit) as an alternative
approach, which puts the information into your Postgres logs, rather than
in the tables themselves.