Is it possible to deferr a trigger until commit, Or to have the
trigger not occur if the transaction is rolled back? Like transaction.
I think its possible since constraints use triggers and if so why
is this a standard feature.
Also is there anyway of seeing what triggers exsist and what they
do? (psql \<somthing> or the like)
Peter Childs
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TIP 1: subscribe and unsubscribe commands go to ma*******@postg resql.org 11  3069 
On Wed, 22 Oct 2003, Peter Childs wrote: Is it possible to deferr a trigger until commit, Or to have the
trigger not occur if the transaction is rolled back? Like transaction.
I think its possible since constraints use triggers and if so why
is this a standard feature.
Also is there anyway of seeing what triggers exsist and what they
do? (psql \<somthing> or the like)
A trigger inside a transaction should automagically roll back should the
transaction fail, shouldn't it?
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scott.marlowe writes: A trigger inside a transaction should automagically roll back should the
transaction fail, shouldn't it?
The database actions that the trigger possibly executed are rolled back
just like any other database actions. But if your trigger does something
external to the database, you have a problem (that borders on
unsolvable).
--
Peter Eisentraut pe*****@gmx.net
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On Wed, 22 Oct 2003, scott.marlowe wrote: On Wed, 22 Oct 2003, Peter Childs wrote:
Is it possible to deferr a trigger until commit, Or to have the
trigger not occur if the transaction is rolled back? Like transaction.
I think its possible since constraints use triggers and if so why
is this a standard feature.
Also is there anyway of seeing what triggers exsist and what they
do? (psql \<somthing> or the like)
A trigger inside a transaction should automagically roll back should the
transaction fail, shouldn't it?
Only if it only affects that database. If the trigger uses C to
tell an outside app whats going on, it will not get the truth.
Background, we are trying to get the database to tell clients when
records get updated, deleted or inserted so that they can update there
on-screen displays without having to query the database every couple of
seconds which would put an unnessary strain on the database. Hence
producing quicker respose times.
Peter Childs
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TIP 8: explain analyze is your friend
On Thu, Oct 23, 2003 at 08:16:27AM +0100, Peter Childs wrote:
On Wed, 22 Oct 2003, scott.marlowe wrote:
On Wed, 22 Oct 2003, Peter Childs wrote:
Is it possible to deferr a trigger until commit, Or to have the
trigger not occur if the transaction is rolled back? Like transaction.
Background, we are trying to get the database to tell clients when
records get updated, deleted or inserted so that they can update there
on-screen displays without having to query the database every couple of
seconds which would put an unnessary strain on the database. Hence
producing quicker respose times.
You should probably be using an AFTER trigger ... when those get
executed, the transaction is ready to commit and will not abort (barring
any major problems, like your server go nuts or something).
But why don't you use some notifications and set up appropiate listeners
on the OSDs? See the NOTIFY/LISTEN reference pages ... these also get
delivered during transaction commit.
--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"In fact, the basic problem with Perl 5's subroutines is that they're not
crufty enough, so the cruft leaks out into user-defined code instead, by
the Conservation of Cruft Principle." (Larry Wall, Apocalypse 6)
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On Thu, 23 Oct 2003, Alvaro Herrera wrote: On Thu, Oct 23, 2003 at 08:16:27AM +0100, Peter Childs wrote:
On Wed, 22 Oct 2003, scott.marlowe wrote:
On Wed, 22 Oct 2003, Peter Childs wrote:
> Is it possible to deferr a trigger until commit, Or to have the
> trigger not occur if the transaction is rolled back? Like transaction.
Background, we are trying to get the database to tell clients when
records get updated, deleted or inserted so that they can update there
on-screen displays without having to query the database every couple of
seconds which would put an unnessary strain on the database. Hence
producing quicker respose times.
You should probably be using an AFTER trigger ... when those get
executed, the transaction is ready to commit and will not abort (barring
any major problems, like your server go nuts or something).
Using an After trigger but the transactions may still rollback. a
subsquent query may fail before commit or a constraint may fail.
But why don't you use some notifications and set up appropiate listeners
on the OSDs? See the NOTIFY/LISTEN reference pages ... these also get
delivered during transaction commit.
Great idea shame drivers to get at these are rare. Anyway you
still need a trigger to fire the notify and these get sent when the query
is done not when its commented. hmmm
Peter Childs
--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"In fact, the basic problem with Perl 5's subroutines is that they're not
crufty enough, so the cruft leaks out into user-defined code instead, by
the Conservation of Cruft Principle." (Larry Wall, Apocalypse 6)
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Peter Childs <bl*********@bl ueyonder.co.uk> writes: Background, we are trying to get the database to tell clients when
records get updated, deleted or inserted so that they can update there
on-screen displays without having to query the database every couple of
seconds which would put an unnessary strain on the database.
Use LISTEN/NOTIFY.
regards, tom lane
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Peter Childs <bl*********@bl ueyonder.co.uk> writes: Great idea shame drivers to get at these are rare. Anyway you
still need a trigger to fire the notify and these get sent when the query
is done not when its commented. hmmm
But the NOTIFY isn't delivered until and unless the transaction commits.
This gets around the AFTER-trigger-can-still-roll-back problem.
regards, tom lane
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TIP 9: the planner will ignore your desire to choose an index scan if your
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On Thu, 23 Oct 2003, Alvaro Herrera wrote: On Thu, Oct 23, 2003 at 08:16:27AM +0100, Peter Childs wrote:
On Wed, 22 Oct 2003, scott.marlowe wrote:
On Wed, 22 Oct 2003, Peter Childs wrote:
> Is it possible to deferr a trigger until commit, Or to have the
> trigger not occur if the transaction is rolled back? Like transaction.
Background, we are trying to get the database to tell clients when
records get updated, deleted or inserted so that they can update there
on-screen displays without having to query the database every couple of
seconds which would put an unnessary strain on the database. Hence
producing quicker respose times.
You should probably be using an AFTER trigger ... when those get
executed, the transaction is ready to commit and will not abort (barring
any major problems, like your server go nuts or something).
This is not true, actually. After triggers generally happen at the end of
statement (with the exception of deferred constraint triggers and some
wierdness with functions) and can themselves throw an exception condition
so even barring internal problems, it's unsafe to assume that an exception
won't happen after your trigger runs.
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TIP 4: Don't 'kill -9' the postmaster
On Thu, 23 Oct 2003, Tom Lane wrote: Peter Childs <bl*********@bl ueyonder.co.uk> writes: Great idea shame drivers to get at these are rare. Anyway you
still need a trigger to fire the notify and these get sent when the query
is done not when its commented. hmmm
But the NOTIFY isn't delivered until and unless the transaction commits.
This gets around the AFTER-trigger-can-still-roll-back problem.
regards, tom lane
Notify is also not very flexable it tells you somthing has
triggerged it not the information that a trigger is supplied with, like
what has changed to what from what.
Peter Childs
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