Database owner installable modules patch - Mailing list pgsql-patches
From | Tom Dunstan |
---|---|
Subject | Database owner installable modules patch |
Date | |
Msg-id | ca33c0a30804061349s41b4d8fcsa9c579454b27ecd2@mail.gmail.com Whole thread Raw |
Responses |
Re: Database owner installable modules patch
Re: Database owner installable modules patch Re: Database owner installable modules patch |
List | pgsql-patches |
Hi all Here is a patch that provides an initial implementation of the module idea that was kicked around over the last few days. While there certainly wasn't consensus on list, enough people seemed interested in the idea of database-owner-installable modules that I thought it was worth having a play with. The general idea, to recap, is to have modules, whether included in the distribution a la contrib or installed separately, installed under a directory such as $pkglib_dir/modules/foo. A typical module directory might contain: - foo.so/foo.dll - install.sql - uninstall.sql - foo.conf - some-other-file-needed-by-foo-module.dat The module would be installed on the system, but the necessary scripts to install it in a particular database have not been run. In particular, the modules would not usually be install in template1. Database owners themselves can then opt to enable a particular installed module in their own database - they do not have to hassle a sysadmin to do it for them. Features of the patch: - A database owner can issue the command "INSTALL MODULE foo", and pgsql will look for a $pkglib_dir/modules/foo/install.sql file to run, and run it. - The install script can do pretty much anything - the user is treated as the superuser for the duration of the script. The main and obvious usage is to create C language functions required by the module. - An entry is created in a new pg_module catalog. This is mainly to guard against someone trying to install a module twice at this point, but it may have other uses in the future (see below). - "UNINSTALL MODULE foo" looks for and executes $pkglib_dir/modules/foo/uninstall.sql and cleans up the catalog. Here is a list of things that are either still to do before I'd consider it worthy of inclusion (should the general approach be considered acceptable), or which I'd like some guidance on: - Currently the script is executed in one big SPI_execute call, and so errors and NOTICEs print out the entire script as context. I'm not sure how to break it up without writing a full parser - we must have something available in the backend to break a string up into multiple statements to execute, but I'm not sure where to look. Also, is there a better way to do this than SPI? - I've hacked in a bit of an end-run around permissions checks to make the current user look like a super-user while a module script is running. Is there a better way to do this? - I can't create C language functions from dlls under the modules dir. I'd like to be able to specify 'modules/foo/foo' as the library name, but the backend sees a slash and decides that must mean the path is absolute. I see two ways to fix this: change the existing code in dfmgr.c to *really* check for absolute/relative paths rather than the current hack, or I could stick in a special case for when it starts with "modules/". I thought I'd get some guidance on-list. Do people think that sticking the dll in with other resources for the module under $pkglib_dir is a bad thing? (I think having everything in one place is a very good thing myself).Is the existing check written the way it is for a particular reason, or is it just "good enough"? - It would be nice to create the empty modules dir when we install pgsql, but while I suppose hacking a Makefile to install it is the way to go, I'm not sure which one would be appropriate. - Hack pgxs to install stuff into a modules dir if we give it some appropriate flag. - I'd like to add pg_depend entries for stuff installed by the module on the pd_module entry, so that you can't drop stuff required by the module without uninstalling the module itself. There would have to be either a function or more syntax to allow a script to do that, or some sort of module descriptor that let the backend do it itself. - Once the issue of loading a dll from inside the module's directory is done, I'd like to look for an e.g. module_install() function inside there, and execute that rather than the install.sql if found. Ditto for uninstall. - Maybe a basic mechanism to allow a module to require another one. Even just a "SELECT require_module('bar')" call at the top of a script. - It would be nice to suppress NOTICEs when installing stuff - the user almost certainly doesn't care. - Pick up config files in module directories, so that a module can install and pick up config for itself rather than getting the sysadmin to hack the global custom_variable_classes setting. - Should plperl etc be done as modules so that their config can live independently as well? And to allow modules to "require" them? Some other nice to haves for some point in the future: - Have some sort of install module privilege, rather than just a check for database ownership - Allow looking for modules under some module path for e.g. /usr/local module installs - Convert existing contrib to modules where appropriate :) - I really have no idea what happens if non-ascii characters are in an install script at the moment. What happens if funky characters are passed to an SPI_execute call? Very far future: - Have pgxs auto-generate rpm .spec files for modules, plus e.g. .deb equivalent, wix files for windows etc etc. - Versioning on modules? General discussion: I see this work as orthogonal to both the CPAN-style distribution / repository discussion, and the fate-of-contrib discussion. If contrib modules are reworked as this sort of module and left in the distribution, they'll be easier to use and more likely to be installed than they are now. If, as Tom suggested, they're mostly moved out of the pgsql source tree and to e.g. pgfoundry or whatever, this mechanism should make them (and every other extension out there) easy to package, install and enable in a user's database. Similarly, I don't personally care for a CPAN-style distribution setup - on my preferred unix-like system I use yum and on windows I prefer installers. Nonetheless, a standardised system to install and enable/disable modules acts as an enabler for all packaging and distribution systems. I'm not sure about the command names - there was already a tendency in the recent discussion to mix the notion of installation of code on the filesystem versus installation into a particular user's database. The convention for doing stuff in a db is CREATE/DROP, but CREATE MODULE doesn't feel right to me, just as I don't really like CREATE LANGUAGE. How about ENABLE/DISABLE MODULE? Makes it clear that the module is installed, it's just not available in this database yet. Thoughts? Anyway, discussion and feedback hereby solicited! Cheers Tom
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