Provided by: liblog-log4perl-perl_1.57-1_all 
NAME
Log::Log4perl::Appender::DBI - implements appending to a DB
SYNOPSIS
my $config = q{
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
#driver attributes support
log4j.appender.DBAppndr.attrs.f_encoding = utf8
};
Log::Log4perl::init ( \$config ) ;
my $logger = Log::Log4perl->get_logger () ;
$logger->warn( $custid, 'big problem!!', $ip_addr );
CAVEAT
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!
DESCRIPTION
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:
• You'd better be darn sure there are not quotes in your log message, or your insert could have
unforeseen consequences! This is a very insecure way to handle database inserts, using place holders
and bind values is much better, keep reading. (Note that the log4j docs warn "Be careful of quotes in
your messages!") *.
• It's not terribly high-performance, a statement is created and executed for each log call.
• The only run-time parameter you get is the %m message, in reality you probably want to log specific
data in specific table columns.
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 '?' placeholder 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.
DESCRIPTION 2
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.
MISC PARAMETERS
usePreparedStmt
See above.
warp_message
see Log::Log4perl::Appender
max_col_size
If you're used to just throwing debugging messages like huge stacktraces into your logger, some
databases (Sybase's DBD!!) may surprise you by choking on data size limitations. Normally, the data
would just be truncated to fit in the column, but Sybases's DBD it turns out maxes out at 255
characters. Use this parameter in such a situation to truncate long messages before they get to the
INSERT statement.
CHANGING DBH CONNECTIONS (POOLING)
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";
}
LIFE OF CONNECTIONS
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), connections might go
stale, but if "Log::Log4perl::Appender::DBI" tries to write a message and figures out that the DB
connection is no longer working (using DBI's ping method), it will reconnect.
The reconnection process can be controlled by two parameters, "reconnect_attempts" and "reconnect_sleep".
"reconnect_attempts" specifies the number of reconnections attempts the DBI appender performs until it
gives up and dies. "reconnect_sleep" is the time between reconnection attempts, measured in seconds.
"reconnect_attempts" defaults to 1, "reconnect_sleep" to 0.
Alternatively, use "Apache::DBI" or "Apache::DBI::Cache" and read CHANGING DB CONNECTIONS above.
Note that "Log::Log4perl::Appender::DBI" holds one connection open for every appender, which might be too
many.
SEE ALSO
Log::Dispatch::DBI
Log::Log4perl::JavaMap::JDBCAppender
LICENSE
Copyright 2002-2013 by Mike Schilli <m@perlmeister.com> and Kevin Goess <cpan@goess.org>.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.
AUTHOR
Please contribute patches to the project on Github:
http://github.com/mschilli/log4perl
Send bug reports or requests for enhancements to the authors via our
MAILING LIST (questions, bug reports, suggestions/patches): log4perl-devel@lists.sourceforge.net
Authors (please contact them via the list above, not directly): Mike Schilli <m@perlmeister.com>, Kevin
Goess <cpan@goess.org>
Contributors (in alphabetical order): Ateeq Altaf, Cory Bennett, Jens Berthold, Jeremy Bopp, Hutton
Davidson, Chris R. Donnelly, Matisse Enzer, Hugh Esco, Anthony Foiani, James FitzGibbon, Carl Franks,
Dennis Gregorovic, Andy Grundman, Paul Harrington, Alexander Hartmaier David Hull, Robert Jacobson,
Jason Kohles, Jeff Macdonald, Markus Peter, Brett Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope,
Lars Thegler, David Viner, Mac Yang.
perl v5.36.0 2022-10-30 Appender::DBI(3pm)