plperl: which version of Perl?
When executing Perl 5 code within the database, PostgreSQL uses the /embedded Perl 5/ to create one (or more) instance of the interpreter. The version of the compiler and virtual machine that runs depends on how PostgreSQL has been compiled, or better, how
libperl.so has been created.
It is possible to use a specific version of Perl without having to change the system wide Perl 5, and in particular it is possible with some effort to use
perlbrew to this aim.
Understanding which perl the database is executing
To know which
perl executable the server will run it is possible to use the
Config module for a little introspection:
# DO LANGUAGE plperlu
$PERL$
use Config;
elog( INFO, 'Perl executable ' . $Config{ perlpath } );
elog( INFO, 'Perl version ' . $Config{ version } );
elog( INFO, 'Perl library ' . $Config{ libperl } );
$PERL$;
For example, the above piece of code produces the following output on my system:
INFO: Perl executable /usr/local/bin/perl
INFO: Perl version 5.24.3
INFO: Perl library libperl.so.5.24.3
that tells clearly the
perl executable is at version
5.24.3.
The same could have been checked from the
plperl.so library file, that is linked to the above version of the library:
% ldd /usr/local/lib/postgresql/plperl.so
/usr/local/lib/postgresql/plperl.so:
libthr.so.3 => /lib/libthr.so.3 (0x801214000)
libperl.so.5.24 => /usr/local/lib/perl5/5.24/mach/CORE/libperl.so.5.24 (0x80143c000)
libc.so.7 => /lib/libc.so.7 (0x800824000)
libm.so.5 => /lib/libm.so.5 (0x801833000)
libcrypt.so.5 => /lib/libcrypt.so.5 (0x801a5e000)
libutil.so.9 => /lib/libutil.so.9 (0x801c7d000)
that is
libperl.so.5.24.
Installing a different plperl version using perlbrew
perlbrew is a great tool to make different versions of Perl 5 co-exist on the same system.
Thanks to
perlbrew** it is possible to install another version of Perl 5 without tossing the system wide installation.
**In order to be usable by PostgreSQL, Perl must be compiled with the shared library option -D useshrplib`**, so as the user that owns the PostgreSQL daemon:
% perlbrew install --multi perl-5.26.2 -D useshrplib
...
% perlbrew switch perl-5.26.2
It is now possible to compile a new version of PostgreSQL, in order to get the new
plperl:
% ./configure --prefix=/opt/postgresql/10/3 --with-perl --with-python --without-readline
...
% ldd /opt/postgresql/10/3/lib/plperl.so
/opt/postgresql/10/3/lib/plperl.so:
libperl.so =>
/var/db/postgres/perl5/perlbrew/perls/perl-5.26.2/lib/5.26.2/amd64-freebsd-multi/CORE/libperl.so
(0x801214000)
libc.so.7 => /lib/libc.so.7 (0x800824000)
libthr.so.3 => /lib/libthr.so.3 (0x801612000)
libm.so.5 => /lib/libm.so.5 (0x80183a000)
libcrypt.so.5 => /lib/libcrypt.so.5 (0x801a65000)
libutil.so.9 => /lib/libutil.so.9 (0x801c84000)
As you can see, the
libperl.so is now linked to the
5.26.2 version of
libperl.so.
It is now time to test the new installation!
# CREATE EXTENSION plperl;
# CREATE LANGUAGE plperlu;
# DO LANGUAGE plperlu
$PERL$
use Config;
elog( INFO, 'Perl executable ' . $Config{ perlpath } );
elog( INFO, 'Perl version ' . $Config{ version } );
elog( INFO, 'Perl library ' . $Config{ libperl } );
$PERL$;
INFO: Perl executable /var/db/postgres/perl5/perlbrew/perls/perl-5.26.2/bin/perl
INFO: Perl version 5.26.2
INFO: Perl library libperl.so
DO
That’s it!