Ref to last INSERT on a table without OIDs?

On Tue, 28 Jan 2003, Mark Cave-Ayland wrote:

Hi there,

Hopefully just a quick one: how is it possible to obtain a reference to
the last inserted record in a table which is created without oids? I
would like to dump/restore some of our larger tables so they don't use
oids, however I am concerned that simply getting the current PK sequence
value after insertion within a transaction is not safe when many people
are accessing the table/sequence at once? Can anyone clarify this? We're
using the latest and greatest 7.3.1.

If you use currval() to get the sequence value it'll be the last value
given to your session so you don't have to worry about other sessions
modifying the sequence.

-----Original Message-----
From: Stephan Szabo [mailto:sszabo@megazone23.bigpanda.com]
Sent: 28 January 2003 16:14
To: Mark Cave-Ayland
Cc: pgsql-general@postgresql.org
Subject: Re: [GENERAL] Ref to last INSERT on a table without OIDs?

On Tue, 28 Jan 2003, Mark Cave-Ayland wrote:

Hi there,

Hopefully just a quick one: how is it possible to obtain a reference

to

the last inserted record in a table which is created without oids? I
would like to dump/restore some of our larger tables so they don't

use

oids, however I am concerned that simply getting the current PK

sequence

value after insertion within a transaction is not safe when many

people

are accessing the table/sequence at once? Can anyone clarify this?

We're

using the latest and greatest 7.3.1.

If you use currval() to get the sequence value it'll be the last value
given to your session so you don't have to worry about other sessions
modifying the sequence.

Hi Stephan,

Thanks for your reply! But I'm still a little confused by what defines a
session - is it a transaction or a backend? I'm just thinking about
connections from web pages which use PHP pooled connections..... if a
session is a transaction then I'm guessing everything should work fine
without any problems?

Cheers,

Mark.

---

Mark Cave-Ayland
Webbased Ltd.
Tamar Science Park
Derriford
Plymouth
PL6 8BX
England

Tel: +44 (0)1752 764445
Fax: +44 (0)1752 764446

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On Tue, 28 Jan 2003, Mark Cave-Ayland wrote:

-----Original Message-----
From: Stephan Szabo [mailto:sszabo@megazone23.bigpanda.com]
Sent: 28 January 2003 16:14
To: Mark Cave-Ayland
Cc: pgsql-general@postgresql.org
Subject: Re: [GENERAL] Ref to last INSERT on a table without OIDs?

On Tue, 28 Jan 2003, Mark Cave-Ayland wrote:

Hi there,

Hopefully just a quick one: how is it possible to obtain a reference

to

the last inserted record in a table which is created without oids? I
would like to dump/restore some of our larger tables so they don't

use

oids, however I am concerned that simply getting the current PK

sequence

value after insertion within a transaction is not safe when many

people

are accessing the table/sequence at once? Can anyone clarify this?

We're

using the latest and greatest 7.3.1.

If you use currval() to get the sequence value it'll be the last value
given to your session so you don't have to worry about other sessions
modifying the sequence.

Thanks for your reply! But I'm still a little confused by what defines a
session - is it a transaction or a backend? I'm just thinking about
connections from web pages which use PHP pooled connections..... if a
session is a transaction then I'm guessing everything should work fine
without any problems?

It's to the backend, but as long as you're asking for the value before you
release the connection to another script you should be fine. If you want
to do something like:

script 1 inserts
- release connection so someone else can get it
script 2 inserts
- release connection
script 1 wants a value

You can't do that without converting it to a different form
script 1 inserts
script 1 saves its inserted value
- release connection
...
- release connection
script 1 retrieves inserted value.

On Tue, Jan 28, 2003 at 14:25:32 -0000,
Mark Cave-Ayland <mark.cave-ayland@webbased.co.uk> wrote:

Hopefully just a quick one: how is it possible to obtain a reference to
the last inserted record in a table which is created without oids? I
would like to dump/restore some of our larger tables so they don't use
oids, however I am concerned that simply getting the current PK sequence
value after insertion within a transaction is not safe when many people
are accessing the table/sequence at once? Can anyone clarify this? We're
using the latest and greatest 7.3.1.

If you are trying to get the primary key of the last record inserted during
the same database session, then using serial for the type of the primary
key and the currval function is exactly what you want.