is an explicit lock necessary? - Mailing list pgsql-sql

From Ash Grove
Subject is an explicit lock necessary?
Date
Msg-id 20060504181056.14509.qmail@web52510.mail.yahoo.com
Whole thread Raw
Responses Re: is an explicit lock necessary?
Re: is an explicit lock necessary?
Re: is an explicit lock necessary?
List pgsql-sql
Hi,

Does beginning a transaction put locks on the tables
queried within the transaction?

In the example below, is #2 necessary? My thought was
that I would need to use an explicit lock to make sure
that the sequence value I'm selecting in #4 is the
same one that is generated from #3. I'm worried about
another instance of the application doing an insert on
table1 between #3 and #4.

1) From my app, I turn off autocommit.
2) I lock table1 in access exclusive mode
3) I do an insert into table1 which generates a
primary key via nextval on sequence1
4) I grab grab the primary key value via currval on
sequence1
5) I do an insert on table2 which includes table1's
primary key so I can join the records later.
6) I manually commit

Thanks!
Ash

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com 


pgsql-sql by date:

Previous
From: Oisin Glynn
Date:
Subject: Re: Connecting to Postgres from other machines (outside localhost)
Next
From: Andrew Sullivan
Date:
Subject: Re: is an explicit lock necessary?