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Appender::DBI(3pm) User Contributed Perl Documentation Appender::DBI(3pm)
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:
o 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!") *.
o It's not terribly high-performance, a statement is created and executed for each log
call.
o 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 AT perlmeister.com> and Kevin Goess <cpan AT 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 AT lists.net
Authors (please contact them via the list above, not directly): Mike Schilli
<m AT perlmeister.com>, Kevin Goess <cpan AT 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 v5.32.1 2021-02-14 Appender::DBI(3pm)
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On Apache
Under GNU General Public License
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