Re: High CPU load on Postgres Server during Peak times!!!!

Gerhard Wiesinger wrote:
> Hello Craig,
>
> Are you sure this is correct?
>
> The test program (see below) with autocommit=0 counts up when an insert
> is done in another session and there is no commit done.
>
> I think with each new select a new implicit transaction is done when no
> explicit "BEGIN" has been established.

Sorry, I should have been more specific. A transaction starts when you do something that will alter data in the database, such as insert, update, alter table, create sequence, and so forth. The Perl DBI won't start a transaction for a select.

But my basic point is still valid: Some languages like Perl can implicitely start a transaction, so if programmers aren't familiar with this behavior, they can accidentally create long-running transactions.

Craig

> Can one confirm this behavior?
>
> Thnx.
>
> Ciao,
> Gerhard
>
> # Disable autocommit!
> my $dbh = DBI->connect($con, $dbuser, $dbpass, {RaiseError => 1,
> AutoCommit=>0}) || die "Unable to access Database '$dbname' on host
> '$dbhost' as user '$dbuser'. Error returned was: ". $DBI::errstr ."";
>
> my $sth = $dbh->prepare('SELECT COUNT(*) FROM employee;');
>
> for (;;)
> {
> $sth->execute();
> my ($count) = $sth->fetchrow();
> print "count=$count\n";
> $sth->finish();
> # $dbh->commit;
> sleep(3);
> }
>
> $dbh->disconnect;
>
> --
> http://www.wiesinger.com/
>
>
> On Thu, 24 Sep 2009, Craig James wrote:
>
>> Dave Dutcher wrote:
>>> You need a COMMIT for every BEGIN. If you just run a SELECT statement
>>> without first beginning a transaction, then you should not end up with a
>>> connection that is Idle in Transaction. If you are beginning a
>>> transaction,
>>> doing a select, and then not committing, then yes that is a bug.
>>
>> The BEGIN can be hidden, though. For example, if the application is
>> written in Perl,
>>
>> $dbh = DBI->connect($dsn, $user, $pass, {AutoCommit => 0});
>>
>> will automatically start a transaction the first time you do
>> anything. Under the covers, the Perl DBI issues the BEGIN for you,
>> and you have to do an explicit
>>
>> $dbh->commit();
>>
>> to commit it.
>>
>> Craig
>>
>>
>>
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>