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triggers in background

Posted on 2004-08-24
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Last Modified: 2012-05-05
Hi all,

in postgresql 7.x,

is there a way to run trigger in background mode ?

What I need is :
 - When a table insert/update/delete, my trigger is running immediately.
But I don't want to wait for trigger's result. My function/procedure will return, trigger will continue to run, even it successfull or not.
Scenerio is something like this.
- I call a function
- The functions inserts or updates a table.
- Trigger relaled to this table fired AFTER INSERT/UPDATE
- Trigger return RETURN NEW always.  But need to be do some works during.
I don't care these works ended or not.

In this scenerio, since trigger running,  my function which has been insert/update the table  does NOT return.

I I want it to be finished as soon as possible. after INSERT/UPDATE without waiting trigger's operation.


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Question by:Ege
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by:rjkimble
ID: 11882965
My guess is that the answer to your question is no. I have encountered situations similar to this, and my approach has been to run an outside cron job periodically -- generally every 5 minutes or so -- and look for new work to be done. You can use your trigger to insert a row in a table that represents a queue of work to be done. The cron job then comes along and looks for records in that queue. If it finds one or more records waiting, it runs a script for each. As it finishes the work for a record, it deletes that record from the table, or it sets a flag indicating that the corresponding task has been accomplished. That strategy has worked well for me.
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by:Ege
ID: 11884276
Sorry,
Guess is not enough to accept. ;)

However, I think your guess is true (I also guess like that)
But, there may be trick. So 250points question I asked.

If not, I hope to be added later. Just running an external program with linux like permissions. Nothing more. This is something like a trigger.
For non SQL operations to be done.
At least for my scenerio, I need it. Instead of running an external program which checks the database from time to time, running it just like a trigger will be better for my project.

PostgreSQL TRUSTED LANGUAGE C supports all functioanlity of C ?

If C language (since PHP as a postgresql language has too many limitations) has no limitation, then it is good.

For example, (not with plpgsql, but C),
I an URL inserted to TABLE,
then can I connect to the URL to get some information inside trigger?
with C like created trigger.

If so, then it is also good for my project. In fact, instead of not waiting triggers result, this POINT is most usufull.

Best regards.

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by:rjkimble
ID: 11884432
You could install PL/Python and use it inside your trigger. That could shell out to the OS and start an external command. That might be a way to accomplish what you want. I have no experience doing that, however.
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by:Ege
ID: 11884476
I don't know PL/Python.
I can use, C, PL/PgSQL, PHP only.

If I can do it by using PL/Python, then I can do it by using C!

or not.

;(
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by:rjkimble
ID: 11884797
Yes -- I suspect you'll be able to do what you want using C.
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by:Ege
ID: 11910286
you will got the points by giving a running example.

Or anybody who gave a running sample, please.

;)

- eGe
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gnudiff earned 250 total points
ID: 11911279
Meaybe a working sample from documentation will work?

http://www.postgresql.org/docs/current/static/trigger-example.html

It shows a complete C example of a trigger function along with neccessary SQL, for PostGres 7.4.
Adding neccessary calls to the trigger to exec some background task (or better pass a message to some daemon which accepts and processes those independently of PG application) should be trivial.
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