Re: questions about transaction and rollback

jing han wrote:

>Hello,
>
>I have questions about transaction and rollback.
>
>Question 1:
>In the postgresql.conf file of our running system,
>autocommit=true. If leave it as true, can we disable
>this attribute when we issue a connection to database?
>
From the DBD::Pg documentation:

The transaction behavior is now controlled with the attribute
AutoCommit. For a complete definition of AutoCommit
please refer to the DBI documentation.

According to the DBI specification the default for AutoCommit is TRUE.
In this mode, any change to the database
becomes valid immediately. Any ’begin’, ’commit’ or ’rollback’ statement
will be rejected.

If AutoCommit is switched-off, immediately a transaction will be started
by issuing a ’begin’ statement.
Any ’commit’ or ’rollback’ will start a new transaction. A disconnect
will issue a ’rollback’ statement.

>
>
>Question 2:
>
>If we use the following command to restore database.
>system("su -l postgres -c \"psql -d dbname -f
>/tmp/db_dump\"");
>
>Can command psql rollback if in the middle of restore
>power failure happens?
>
If the db_dump file starts with a transaction yes.

>
>
>Question 3:
>
>During restore, if power failure happens, we want to
>rollback everything having been inserted or updated to
>database. In another word, if we are restoring a
>database with thousands of turples changes, at the
>time, we restore the last turple, power failure
>happens, we want to rollback. Can postgres support
>huge data changes in one transaction block?
>
Yes.

> How to
>configure the limit of how much we can do in one
>transaction block?
>
That would be controlled by issuing multiple transactions.

>
>
>Hope to hear from you soon and thank you in advance.
>
Sincerely,

Joshua D. Drake

>
>
>Best Regards
>
>jing
>
>
>
>__________________________________
>Do you Yahoo!?
>Yahoo! Small Business - Try our new resources site!
>http://smallbusiness.yahoo.com/resources/
>
>---------------------------(end of broadcast)---------------------------
>TIP 8: explain analyze is your friend
>