45.4. Global Values in PL/Perl

45.4. Global Values in PL/Perl
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+ You can use the global hash %_SHARED to store + data, including code references, between function calls for the + lifetime of the current session. +

+ Here is a simple example for shared data: +

+CREATE OR REPLACE FUNCTION set_var(name text, val text) RETURNS text AS $$
+    if ($_SHARED{$_[0]} = $_[1]) {
+        return 'ok';
+    } else {
+        return "cannot set shared variable $_[0] to $_[1]";
+    }
+$$ LANGUAGE plperl;
+
+CREATE OR REPLACE FUNCTION get_var(name text) RETURNS text AS $$
+    return $_SHARED{$_[0]};
+$$ LANGUAGE plperl;
+
+SELECT set_var('sample', 'Hello, PL/Perl!  How''s tricks?');
+SELECT get_var('sample');
+

+ Here is a slightly more complicated example using a code reference: + +

+CREATE OR REPLACE FUNCTION myfuncs() RETURNS void AS $$
+    $_SHARED{myquote} = sub {
+        my $arg = shift;
+        $arg =~ s/(['\\])/\\$1/g;
+        return "'$arg'";
+    };
+$$ LANGUAGE plperl;
+
+SELECT myfuncs(); /* initializes the function */
+
+/* Set up a function that uses the quote function */
+
+CREATE OR REPLACE FUNCTION use_quote(TEXT) RETURNS text AS $$
+    my $text_to_quote = shift;
+    my $qfunc = $_SHARED{myquote};
+    return &$qfunc($text_to_quote);
+$$ LANGUAGE plperl;
+

+ + (You could have replaced the above with the one-liner + return $_SHARED{myquote}->($_[0]); + at the expense of readability.) +

+ For security reasons, PL/Perl executes functions called by any one SQL role + in a separate Perl interpreter for that role. This prevents accidental or + malicious interference by one user with the behavior of another user's + PL/Perl functions. Each such interpreter has its own value of the + %_SHARED variable and other global state. Thus, two + PL/Perl functions will share the same value of %_SHARED + if and only if they are executed by the same SQL role. In an application + wherein a single session executes code under multiple SQL roles (via + SECURITY DEFINER functions, use of SET ROLE, etc.) + you may need to take explicit steps to ensure that PL/Perl functions can + share data via %_SHARED. To do that, make sure that + functions that should communicate are owned by the same user, and mark + them SECURITY DEFINER. You must of course take care that + such functions can't be used to do anything unintended. +

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45.3. Built-in Functions	Home	45.5. Trusted and Untrusted PL/Perl