Thread: How to isolate the result of SELECT's?
Hi, I need to do an operation that I will use some SELECT's and get the results, but I want to have sure that those tables have not been changed with INSERT's or UPDATES during the operation. Example: BEGIN OPERATION Select field from table1; ... Select other_field from table2; ... END OPERATION How can I lock these tables to assure that the tables are not getting INSERTS's or UPDATE's during the operation? Best Regards,
On Sun, Mar 18, 2012 at 6:33 PM, Andre Lopes <lopes80andre@gmail.com> wrote:
Isn't that what 'begin transaction' and 'commit' are for?
Hi,
I need to do an operation that I will use some SELECT's and get the
results, but I want to have sure that those tables have not been
changed with INSERT's or UPDATES during the operation.
Example:
BEGIN OPERATION
Select field from table1;
...
Select other_field from table2;
...
END OPERATION
How can I lock these tables to assure that the tables are not getting
INSERTS's or UPDATE's during the operation?
Best Regards,\
Isn't that what 'begin transaction' and 'commit' are for?
--
Mike Nolan
Mike Nolan
On 03/18/2012 04:33 PM, Andre Lopes wrote: > Hi, > > I need to do an operation that I will use some SELECT's and get the > results, but I want to have sure that those tables have not been > changed with INSERT's or UPDATES during the operation. > > Example: > > BEGIN OPERATION > Select field from table1; > ... > Select other_field from table2; > ... > END OPERATION > > How can I lock these tables to assure that the tables are not getting > INSERTS's or UPDATE's during the operation? Rather than replicate the docs in a post, I suggest you take a look at: http://www.postgresql.org/docs/9.1/interactive/mvcc.html It explains the various options you have very well. > > Best Regards, > -- Adrian Klaver adrian.klaver@gmail.com
Hi,
>
> I need to do an operation that I will use some SELECT's and get the
> results, but I want to have sure that those tables have not been
> changed with INSERT's or UPDATES during the operation.
>
> Example:
>
> BEGIN OPERATION
> Select field from table1;
> ...
> Select other_field from table2;
> ...
> END OPERATION
>
> How can I lock these tables to assure that the tables are not getting
> INSERTS's or UPDATE's during the operation?
>
If you set transaction isolation level to repeatable, the tables may undergo changes, but you will get repeatable reads. Explicitly locking the tables is another option.
http://www.postgresql.org/docs/current/static/explicit-locking.html
Regards,
Jayadevan
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>
> I need to do an operation that I will use some SELECT's and get the
> results, but I want to have sure that those tables have not been
> changed with INSERT's or UPDATES during the operation.
>
> Example:
>
> BEGIN OPERATION
> Select field from table1;
> ...
> Select other_field from table2;
> ...
> END OPERATION
>
> How can I lock these tables to assure that the tables are not getting
> INSERTS's or UPDATE's during the operation?
>
If you set transaction isolation level to repeatable, the tables may undergo changes, but you will get repeatable reads. Explicitly locking the tables is another option.
http://www.postgresql.org/docs/current/static/explicit-locking.html
Regards,
Jayadevan
DISCLAIMER:
"The information in this e-mail and any attachment is intended only for the person to whom it is addressed and may contain confidential and/or privileged material. If you have received this e-mail in error, kindly contact the sender and destroy all copies of the original communication. IBS makes no warranty, express or implied, nor guarantees the accuracy, adequacy or completeness of the information contained in this email or any attachment and is not liable for any errors, defects, omissions, viruses or for resultant loss or damage, if any, direct or indirect."
In all likelihood you do not want to do what you described (lock the tables.) You have to have a basic understanding ofMVCC and transaction isolation levels to determine if the default behavior of mvcc + 'read committed' is sufficient. Ina lot of cases it is. Kiriakos On Mar 18, 2012, at 7:33 PM, Andre Lopes wrote: > Hi, > > I need to do an operation that I will use some SELECT's and get the > results, but I want to have sure that those tables have not been > changed with INSERT's or UPDATES during the operation. > > Example: > > BEGIN OPERATION > Select field from table1; > ... > Select other_field from table2; > ... > END OPERATION > > How can I lock these tables to assure that the tables are not getting > INSERTS's or UPDATE's during the operation? > > Best Regards, > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general