1Apache::DBI(3) User Contributed Perl Documentation Apache::DBI(3)
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6 Apache::DBI - Initiate a persistent database connection
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9 # Configuration in httpd.conf or startup.pl:
10 PerlModule Apache::DBI # this comes before all other modules using DBI
12 Do NOT change anything in your scripts. The usage of this module is
14 absolutely transparent !
15
17 This module initiates a persistent database connection.
18 The database access uses Perl's DBI. For supported DBI drivers see:
20 http://dbi.perl.org/
22 When loading the DBI module (do not confuse this with the Apache::DBI
24 module) it checks if the environment variable 'MOD_PERL' has been set
25 and if the module Apache::DBI has been loaded. In this case every
26 connect request will be forwarded to the Apache::DBI module. This
27 checks if a database handle from a previous connect request is already
28 stored and if this handle is still valid using the ping method. If
29 these two conditions are fulfilled it just returns the database handle.
30 The parameters defining the connection have to be exactly the same,
31 including the connect attributes! If there is no appropriate database
32 handle or if the ping method fails, a new connection is established and
33 the handle is stored for later re-use. There is no need to remove the
34 disconnect statements from your code. They won't do anything because
35 the Apache::DBI module overloads the disconnect method.
36 The Apache::DBI module still has a limitation: it keeps database
38 connections persistent on a per process basis. The problem is, if a
39 user accesses a database several times, the http requests will be
40 handled very likely by different processes. Every process needs to do
41 its own connect. It would be nice if all servers could share the
42 database handles, but currently this is not possible because of the
43 distinct memory-space of each process. Also it is not possible to
44 create a database handle upon startup of the httpd and then inherit
45 this handle to every subsequent server. This will cause clashes when
46 the handle is used by two processes at the same time. Apache::DBI has
47 built-in protection against this. It will not make a connection
48 persistent if it sees that it is being opened during the server
49 startup. This allows you to safely open a connection for grabbing data
50 needed at startup and disconnect it normally before the end of startup.
51 With this limitation in mind, there are scenarios, where the usage of
53 Apache::DBI is depreciated. Think about a heavy loaded Web-site where
54 every user connects to the database with a unique userid. Every server
55 would create many database handles each of which spawning a new backend
56 process. In a short time this would kill the web server.
57 Another problem are timeouts: some databases disconnect the client
59 after a certain period of inactivity. The module tries to validate the
60 database handle using the "ping()" method of the DBI-module. This
61 method returns true by default. Most DBI drivers have a working
62 "ping()" method, but if the driver you're using doesn't have one and
63 the database handle is no longer valid, you will get an error when
64 accessing the database. As a work-around you can try to add your own
65 "ping()" method using any database command which is cheap and safe, or
66 you can deactivate the usage of the ping method (see CONFIGURATION
67 below).
68 Here is a generalized ping method, which can be added to the driver
70 module:
71 package DBD::xxx::db; # ====== DATABASE ======
73 use strict;
74 sub ping {
76 my ($dbh) = @_;
77 my $ret = 0;
78 eval {
79 local $SIG{__DIE__} = sub { return (0); };
80 local $SIG{__WARN__} = sub { return (0); };
81 # adapt the select statement to your database:
82 $ret = $dbh->do('select 1');
83 };
84 return ($@) ? 0 : $ret;
85 }
86 Transactions: a standard DBI script will automatically perform a
88 rollback whenever the script exits. In the case of persistent database
89 connections, the database handle will not be destroyed and hence no
90 automatic rollback will occur. At a first glance it even seems possible
91 to handle a transaction over multiple requests. But this should be
92 avoided, because different requests are handled by different processes
93 and a process does not know the state of a specific transaction which
94 has been started by another process. In general, it is good practice to
95 perform an explicit commit or rollback at the end of every request. In
96 order to avoid inconsistencies in the database in case AutoCommit is
97 off and the script finishes without an explicit rollback, the
98 Apache::DBI module uses a PerlCleanupHandler to issue a rollback at the
99 end of every request. Note, that this CleanupHandler will only be used,
100 if the initial data_source sets AutoCommit = 0 or AutoCommit is turned
101 off, after the connect has been done (ie begin_work). However, because
102 a connection may have set other parameters, the handle is reset to its
103 initial connection state before it is returned for a second time.
104 This module plugs in a menu item for Apache::Status or Apache2::Status.
106 The menu lists the current database connections. It should be
107 considered incomplete because of the limitations explained above. It
108 shows the current database connections for one specific process, the
109 one which happens to serve the current request. Other processes might
110 have other database connections. The Apache::Status/Apache2::Status
111 module has to be loaded before the Apache::DBI module !
112
114 The module should be loaded upon startup of the Apache daemon. Add the
115 following line to your httpd.conf or startup.pl:
116 PerlModule Apache::DBI
118 It is important, to load this module before any other modules using DBI
120 !
121 A common usage is to load the module in a startup file called via the
123 PerlRequire directive. See eg/startup.pl and eg/startup2.pl for
124 examples.
125 There are two configurations which are server-specific and which can be
127 done upon server startup:
128 Apache::DBI->connect_on_init($data_source, $username, $auth, \%attr)
130 This can be used as a simple way to have apache servers establish
132 connections on process startup.
133 Apache::DBI->setPingTimeOut($data_source, $timeout)
135 This configures the usage of the ping method, to validate a connection.
137 Setting the timeout to 0 will always validate the database connection
138 using the ping method (default). Setting the timeout < 0 will de-
139 activate the validation of the database handle. This can be used for
140 drivers, which do not implement the ping-method. Setting the timeout >
141 0 will ping the database only if the last access was more than timeout
142 seconds before.
143 For the menu item 'DBI connections' you need to call
145 Apache::Status/Apache2::Status BEFORE Apache::DBI ! For an example of
146 the configuration order see startup.pl.
147 To enable debugging the variable $Apache::DBI::DEBUG must be set. This
149 can either be done in startup.pl or in the user script. Setting the
150 variable to 1, just reports about a new connect. Setting the variable
151 to 2 enables full debug output.
152
154 MOD_PERL 2.0
155 Apache::DBI version 0.96 and later should work under mod_perl 2.0 RC5
156 and later with httpd 2.0.49 and later.
157 Apache::DBI versions less than 1.00 are NO longer supported.
159 Additionally, mod_perl versions less then 2.0.0 are NO longer
160 supported.
161 MOD_PERL 1.0 Note that this module needs mod_perl-1.08 or higher,
163 apache_1.3.0 or higher and that mod_perl needs to be configured with
164 the appropriate call-back hooks:
165 PERL_CHILD_INIT=1 PERL_STACKED_HANDLERS=1
166 Apache::DBI v0.94 was the last version before dual mod_perl 2.x support
168 was begun. It still recommended that you use the latest version of
169 Apache::DBI because Apache::DBI versions less than 1.00 are NO longer
170 supported.
171
173 Note that this module is intended for use in porting existing DBI code
174 to mod_perl, or writing code that can run under both mod_perl and CGI.
175 If you are using a database abstraction layer such as Class::DBI or
176 DBIx::Class that already manages persistent connections for you, there
177 is no need to use this module in addition. (Another popular choice,
178 Rose::DB::Object, can cooperate with Apache::DBI or use your own custom
179 connection handling.) If you are developing new code that is strictly
180 for use in mod_perl, you may choose to use "DBI->connect_cached()"
181 instead, but consider adding an automatic rollback after each request,
182 as described above.
183
185 Apache, mod_perl, DBI
186
188 • Philip M. Gollucci <pgollucci@p6m7g8.com> is currently packaging
189 new releases.
190 Ask Bjoern Hansen <ask@develooper.com> packaged a large number of
192 releases.
193 • Edmund Mergl was the original author of Apache::DBI. It is now
195 supported and maintained by the modperl mailinglist, see the
196 mod_perl documentation for instructions on how to subscribe.
197 • mod_perl by Doug MacEachern.
199 • DBI by Tim Bunce <dbi-users-subscribe@perl.org>
201
203 The Apache::DBI module is free software; you can redistribute it and/or
204 modify it under the same terms as Perl itself.
205perl v5.34.0 2021-07-22 Apache::DBI(3)