Log::Log4perl::Appender::DBI - implements appending to a DB
my $config = <<'EOT';
log4j.category = WARN, DBAppndr
log4j.appender.DBAppndr = Log::Log4perl::Appender::DBI
log4j.appender.DBAppndr.datasource = DBI:CSV:f_dir=t/tmp
log4j.appender.DBAppndr.username = bobjones
log4j.appender.DBAppndr.password = 12345
log4j.appender.DBAppndr.sql = \
insert into log4perltest \
(loglevel, custid, category, message, ipaddr) \
values (?,?,?,?,?)
log4j.appender.DBAppndr.params.1 = %p
#2 is custid from the log() call
log4j.appender.DBAppndr.params.3 = %c
#4 is the message from log()
#5 is ipaddr from log()
log4j.appender.DBAppndr.usePreparedStmt = 1
#--or--
log4j.appender.DBAppndr.bufferSize = 2
#just pass through the array of message items in the log statement
log4j.appender.DBAppndr.layout = Log::Log4perl::Layout::NoopLayout
log4j.appender.DBAppndr.warp_message = 0
$logger->warn( $custid, 'big problem!!', $ip_addr );
This is a very young module and there are a lot of variations in setups with different databases and connection methods, so make sure you test thoroughly! Any feedback is welcome!
This is a specialized Log::Dispatch object customized to work with log4perl and its abilities, originally based on Log::Dispatch::DBI by Tatsuhiko Miyagawa but with heavy modifications.
It is an attempted compromise between what Log::Dispatch::DBI was doing and what log4j's JDBCAppender does. Note the log4j docs say the JDBCAppender "is very likely to be completely replaced in the future."
The simplest usage is this:
log4j.category = WARN, DBAppndr
log4j.appender.DBAppndr = Log::Log4perl::Appender::DBI
log4j.appender.DBAppndr.datasource = DBI:CSV:f_dir=t/tmp
log4j.appender.DBAppndr.username = bobjones
log4j.appender.DBAppndr.password = 12345
log4j.appender.DBAppndr.sql = \
INSERT INTO logtbl \
(loglevel, message) \
VALUES ('%c','%m')
log4j.appender.DBAppndr.layout = Log::Log4perl::Layout::PatternLayout
$logger->fatal('fatal message');
$logger->warn('warning message');
===============================
|FATAL|fatal message |
|WARN |warning message |
===============================
But the downsides to that usage are:
So let's try using placeholders, and tell the logger to create a prepared statement handle at the beginning and just reuse it (just like Log::Dispatch::DBI does)
log4j.appender.DBAppndr.sql = \
INSERT INTO logtbl \
(custid, loglevel, message) \
VALUES (?,?,?)
#---------------------------------------------------
#now the bind values:
#1 is the custid
log4j.appender.DBAppndr.params.2 = %p
#3 is the message
#---------------------------------------------------
log4j.appender.DBAppndr.layout = Log::Log4perl::Layout::NoopLayout
log4j.appender.DBAppndr.warp_message = 0
log4j.appender.DBAppndr.usePreparedStmt = 1
$logger->warn( 1234, 'warning message' );
Now see how we're using the '?' placeholders in our statement? This means we don't have to worry about messages that look like
invalid input: 1234';drop table custid;
fubaring our database!
Normally a list of things in the logging statement gets concatenated into
a single string, but setting warp_message to 0 and using the
NoopLayout means that in
$logger->warn( 1234, 'warning message', 'bgates' );
the individual list values will still be available for the DBI appender later
on. (If warp_message is not set to 0, the default behavior is to
join the list elements into a single string. If PatternLayout or SimpleLayout
are used, their attempt to render() your layout will result in something
like "ARRAY(0x841d8dc)" in your logs. More information on warp_message
is in Log::Log4perl::Appender.)
In your insert SQL you can mix up '?' placeholders with conversion specifiers (%c, %p, etc) as you see fit--the logger will match the question marks to params you've defined in the config file and populate the rest with values from your list. If there are more '?' placeholders than there are values in your message, it will use undef for the rest. For instance,
log4j.appender.DBAppndr.sql = \ insert into log4perltest \ (loglevel, message, datestr, subpoena_id)\ values (?,?,?,?) log4j.appender.DBAppndr.params.1 = %p log4j.appender.DBAppndr.params.3 = %d
log4j.appender.DBAppndr.warp_message=0
$logger->info('arrest him!', $subpoena_id);
results in the first '?' placholder being bound to %p, the second to "arrest him!", the third to the date from "%d", and the fourth to your $subpoenaid. If you forget the $subpoena_id and just log
$logger->info('arrest him!');
then you just get undef in the fourth column.
If the logger statement is also being handled by other non-DBI appenders,
they will just join the list into a string, joined with
$Log::Log4perl::JOIN_MSG_ARRAY_CHAR (default is an empty string).
And see the usePreparedStmt? That creates a statement handle when
the logger object is created and just reuses it. That, however, may
be problematic for long-running processes like webservers, in which case
you can use this parameter instead
log4j.appender.DBAppndr.bufferSize=2
This copies log4j's JDBCAppender's behavior, it saves up that many log statements and writes them all out at once. If your INSERT statement uses only ? placeholders and no %x conversion specifiers it should be quite efficient because the logger can re-use the same statement handle for the inserts.
If the program ends while the buffer is only partly full, the DESTROY block should flush the remaining statements, if the DESTROY block runs of course.
* As I was writing this, Danko Mannhaupt was coming out with his improved log4j JDBCAppender (http://www.mannhaupt.com/danko/projects/) which overcomes many of the drawbacks of the original JDBCAppender.
Or another way to say the same thing:
The idea is that if you're logging to a database table, you probably want specific parts of your log information in certain columns. To this end, you pass an list to the log statement, like
$logger->warn('big problem!!',$userid,$subpoena_nr,$ip_addr);
and the array members drop into the positions defined by the placeholders in your SQL statement. You can also define information in the config file like
log4j.appender.DBAppndr.params.2 = %p
in which case those numbered placeholders will be filled in with the specified values, and the rest of the placeholders will be filled in with the values from your log statement's array.
If you want to get your dbh from some place in particular, like maybe a pool, subclass and override _init() and/or create_statement(), for instance
sub _init {
; #no-op, no pooling at this level
}
sub create_statement {
my ($self, $stmt) = @_;
$stmt || croak "Log4perl: sql not set in ".__PACKAGE__;
return My::Connections->getConnection->prepare($stmt)
|| croak "Log4perl: DBI->prepare failed $DBI::errstr\n$stmt";
}
If you're using log4j.appender.DBAppndr.usePreparedStmt
this module creates an sth when it starts and keeps it for the life
of the program. For long-running processes (e.g. mod_perl) this
may be a problem, your connections may go stale.
It also holds one connection open for every appender, which might be too many.
Even if you're not using that, the database handle may go stale. If you're not using Apache::DBI this may cause you problems. See CHANGING DB CONNECTIONS above.
Kevin Goess <cpan@goess.org> December, 2002