public inbox for [email protected]  

help / color / mirror / Atom feed

From: veem v <[email protected]>
To: Adrian Klaver <[email protected]>
Cc: pgsql-general <[email protected]>
Subject: Re: Question on trigger
Date: Sat, 13 Apr 2024 12:33:47 +0530
Message-ID: <CAB+=1TUnCwVvHSMS2+wqV8f5OpiKXwkrJ3CDJ_JpRZEQomw=Ew@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <CAB+=1TV2rVqySeVeviDfoKc0ApiLPQ9=i=5PM9R6ek-_aKuhOg@mail.gmail.com>
	<[email protected]>

Thank you Adrian.

So it seems the heavy DML tables will see an impact if having triggers
(mainly for each row trigger) created on them.

And also the bulk DML/array based insert (which inserts multiple rows in
one short or one batch) , in those cases it seems the trigger will not make
that happen as it will force it to make it happen row by row, as the
trigger is row based. Will test anyway though.

On Thu, 11 Apr 2024 at 22:00, Adrian Klaver <[email protected]>
wrote:

> On 4/11/24 07:31, veem v wrote:
> > Hi, We used to use Oracle database in which we had audit
> > triggers(something as below) mandated for all tables by the control
> > team. Now we are going to use the postgresql 15.4 database for one of
> > our applications. So,wanted to understand if there exists any downside
> > of such audit trigger setup for all the tables? Will it impact the bulk
> > data insert/update/delete OR slowdown of any of the DML operations
> > significantly (and thus will not be advisable to use for all tables but
> > selected ones)?
>
> Triggers are overhead in Postgres as they where in Oracle. If they
> didn't cause an issue in Oracle I would suspect that would also be the
> case in Postgres. To confirm you would need to create a test setup and
> run some common operations and see what the overhead is.
>
> Some potential performance improvements:
>
> https://www.postgresql.org/docs/current/sql-createtrigger.html
>
> "...a trigger that is marked FOR EACH STATEMENT only executes once for
> any given operation, regardless of how many rows it modifies (in
> particular, an operation that modifies zero rows will still result in
> the execution of any applicable FOR EACH STATEMENT triggers)."
>
> <...>
>
> "The REFERENCING option enables collection of transition relations,
> which are row sets that include all of the rows inserted, deleted, or
> modified by the current SQL statement. This feature lets the trigger see
> a global view of what the statement did, not just one row at a time.
> This option is only allowed for an AFTER trigger that is not a
> constraint trigger; also, if the trigger is an UPDATE trigger, it must
> not specify a column_name list. OLD TABLE may only be specified once,
> and only for a trigger that can fire on UPDATE or DELETE; it creates a
> transition relation containing the before-images of all rows updated or
> deleted by the statement. Similarly, NEW TABLE may only be specified
> once, and only for a trigger that can fire on UPDATE or INSERT; it
> creates a transition relation containing the after-images of all rows
> updated or inserted by the statement."
>
>
> As example:
>
> https://www.postgresql.org/docs/current/plpgsql-trigger.html
>
> Example 43.7. Auditing with Transition Tables
>
> >
> > CREATE OR REPLACE TRIGGER TAB_AUD_TRG
> >    BEFORE DELETE OR INSERT OR UPDATE
> >    ON tab
> >    FOR EACH ROW
> > BEGIN
> >        IF inserting THEN
> >          :NEW.create_timestamp := systimestamp;
> >          :NEW.create_userid  := sys_context('USERENV','SESSION_USER');
> >          :NEW.update_timestamp := systimestamp;
> >          :NEW.update_userid := sys_context('USERENV','SESSION_USER');
> >        ELSIF updating THEN
> >          IF  updating('create_userid') OR updating('create_timestamp')
> THEN
> >              :new.create_userid   := :old.create_userid;
> >              :new.create_timestamp  := :old.create_timestamp;
> >          END IF;
> >          :NEW.update_timestamp := systimestamp;
> >          :NEW.update_userid := sys_context('USERENV','SESSION_USER');
> >        END IF;
> >    END;
> > /
> >
> > Regards
> > Veem
>
> --
> Adrian Klaver
> [email protected]
>
>

view thread (4+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected]
  Subject: Re: Question on trigger
  In-Reply-To: <CAB+=1TUnCwVvHSMS2+wqV8f5OpiKXwkrJ3CDJ_JpRZEQomw=Ew@mail.gmail.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox