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
};
$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.