On 13/2/20 5:58 pm, JohnD Blackburn wrote:
The DBA pulled info from some cache that showed the SQL statement from the
script was executed 12610 times.
So if I were to add an “or die $!” statement after the fetchrow_array(), that might fix things? (or prevent it from trying to continue if there are
errors?)
Or catch errors after the execute statement?
Error checking after each call is a good idea.
The prepare() (if my implementation refreshing skills are accurate) maps to an Oracle call that does a lightweight parse to check things like bind
variables and quotes. Most errors will come from the execute() - bogus syntax, wrong columns, DB space errors etc.
Chris
*From:* Christopher Jones <christopher.jo...@oracle.com>
*Sent:* Thursday, 13 February 2020 12:56 PM
*To:* dbi-users@perl.org; JohnD Blackburn <johnd.blackb...@au.abb.com>
*Subject:* Re: Perl script excessively executing statement
*CAUTION:*This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know
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On 13/2/20 11:13 am, JohnD Blackburn wrote:
Is that a behavior of DBI or DBD::Oracle?
Maybe your script, if you are blindly looping when it gets an error? Overall, I don't think there is enough information to point directly at a
cause. Presumably the DBA meant that a SQL statement (of some kind) was e
xecuted 12610 times; not that your script was invoked that number of times.
My script says prepare or die, so any retries would have had to come
directly from the DBD::Oracle module
Script basically says:
use DBD::Oracle;
my $dbh = DBI->connect("dbi:Oracle:$dbSID", $user, $passwd, {AutoCommit =>
0 });
my $statement = <<END;
20 line select statement
END
Somewhere you might want to tune ora_prefetch_rows or RowCacheSize, depending how many rows you expect the query to return. This is unrelated to
your question.
my $arraySelect = $dbh->prepare($statement) or die $!;
$arraySelect->execute();
while ( my ($var1, $var2, $var3, $var4) = $arraySelect->fetchrow_array() ) {
<perl code to process row of data which includes a couple of “if next”
statement blocks with no reference to arraySelect inside the while loop>
}
$arraySelect->finish();
$dbh->disconnect();
I don’t work much with the DBD::Oracle module or perl and what I have is
just reworked from scripts others have written.
Is there parameters for the DBD::Oracle functions that can affect their
behavior? If this is behavior of the execute function, I really need to
be able to reign it in to limit its impact if it ever does it again. Not
knowing why the issue triggered in the 1^st place, I don’t know how to
reproduce it to test if any mitigations are sufficient.
You can set sqlnet.ora parameters to bound the time taken for connection and statement execution. Refer to
https://cx-oracle.readthedocs.io/en/latest/user_guide/ha.html#network-configuration
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and https://oracle.github.io/node-oracledb/doc/api.html#connectionha
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since the sqlnet.ora settings will be the same for DBD::Oracle - the network layer is common across all the C-based drivers. Depending on your
requirements, you may want to sleep between retries.
Chris
Cheers,
John
*From:* Geoffrey Rommel <wgrom...@gmail.com> <mailto:wgrom...@gmail.com>
*Sent:* Thursday, 13 February 2020 2:56 AM
*To:* JohnD Blackburn <johnd.blackb...@au.abb.com>
<mailto:johnd.blackb...@au.abb.com>
*Cc:* dbi-users@perl.org <mailto:dbi-users@perl.org>
*Subject:* Re: Perl script excessively executing statement
*CAUTION:*This email originated from outside of the organization. Do not
click links or open attachments unless you recognize the sender and
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I don't work with Oracle, but here's a guess. Maybe the database was
unresponsive before your script started running, not as a result of it. If
so, maybe your script tried to prepare the statement, failed, and retried
12000 times. Eventually the DBA noticed the problem and restarted the
database, at which time your script was terminated along with everything
else.
On Tue, Feb 11, 2020 at 11:56 PM JohnD Blackburn <johnd.blackb...@au.abb.com
<mailto:johnd.blackb...@au.abb.com>> wrote:
Hi all,
I have a perl script in my monitoring system that has been working for
months without an issue.
Basically, it connects to an Oracle 12c database, prepares a statement,
then it executes the statement, then it has a while loop to process
the returned rows.
So under normal conditions the statement is executed once every 5
minutes.
Now on Friday last week, it did something really strange which I cannot
account for the behaviour.
According to the DBA, the statement in the script was executed 12610
times over a 50 minute period causing the database to become
non-responsive. The DBAs also stated that the script only connected to
the database once at the beginning of the 50 minute period. Average
execution time of the statement was 0.26 seconds.
According to the log for my script, the script only executed once at
the beginning of the 50 minute period, and then after that, returned to
executing every 5 minutes.
Since that incident, the statememt in question has only executed the
expected 12 times per hour.
I have yet to find a satisfactory reason the SQL statement from this
perl script executed so many times in the 50 minute period.
Script is running on an Oracle Linux 7.7 server with;
* oracle 12c client installed
* perl 5.16.3
* perl-DBI 1.627-4 ( from Oracle Linix Latest yum repository)
* perl-DBD-ODBC 1.50.-3 (from EPEL)
* DBD::Oracle 1.80 (from CPAN)
Oracle 12 database is on a remote server.
Anyone have any ideas why the SQL statement would have been executed
12000+ times in a 50minute period, when the script and its schedule
should not have executed the SQL any more frequiently than 12 times an
hour?
Regards,
John
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