"korryd@enterprisedb.com" <korryd@enterprisedb.com> writes:
The attached patch adds support for loadable instrumentation plugins for
procedural languages (as discussed at the anniversary summit). It also
adds plugin support to the PL/pgSQL language handler.
In view of the other patch submitted to support init/fini functions for
shared libraries, I'm inclined to change this one to depend on that;
in particular it seems like we could eliminate the necessity for users
to specify the correct setup-function names. Thoughts?

regards, tom lane

Search Discussions

  • Korryd at Aug 8, 2006 at 5:36 pm

    In view of the other patch submitted to support init/fini functions for
    shared libraries, I'm inclined to change this one to depend on that;
    in particular it seems like we could eliminate the necessity for users
    to specify the correct setup-function names. Thoughts?


    I think that would be great. Can you point me to the patch you're
    referring to? I can convert my patch if you prefer.

    -- Korry


    --
    Korry Douglas korryd@enterprisedb.com
    EnterpriseDB http://www.enterprisedb.com
  • Tom Lane at Aug 9, 2006 at 4:44 pm
    Yesterday I suggested that we should redesign the PL plugin patch:
    http://archives.postgresql.org/pgsql-patches/2006-07/msg00291.php
    in view of the recently-committed patch to add initialization/
    finalization support for all dynamic libraries loaded into the backend:
    http://archives.postgresql.org/pgsql-committers/2006-08/msg00176.php

    That was just handwaving at the time, because I didn't have a concrete
    proposal, but here is one.

    Overview
    --------

    ISTM there are two separate bits of functionality that the core backend
    needs to provide in support of PL plugins. The first is that we need a
    "rendezvous" facility whereby two separately-loaded shared libraries can
    connect and exchange data (a struct of function pointers for the immediate
    plans for plpgsql, but in general it might be anything). The exchanged
    data mustn't be limited to things known in advance to the core backend.
    The facility should support loading of communicating libraries in either
    order, and it should also allow for unloading of libraries. This seems
    easy enough to design: the core backend should basically provide a
    hashtable that maps names to "void *" pointer variables, and then two
    libraries that want to communicate just agree on a name and the data
    structure to be pointed to. (More details below.)

    The other, probably more controversial bit of functionality is that there
    needs to be a way to cause a backend to load a PL plugin shared library
    without any cooperation from the connected client application. For
    interactive use of a PL debugger it might be sufficient to tell people to
    do "LOAD 'plpgsql_debugger'" before running their function-to-be-tested,
    but if you're trying to debug some behavior that only manifests in a large
    complicated application, it may be impractical to get the application to
    issue such a command. We agreed while discussing this at the PG
    Anniversary Conference that providing a GUC variable for this purpose is
    probably sufficient, as there are multiple ways that such a variable can
    be set on behalf of an application: ALTER USER SET, ALTER DATABASE SET,
    "export PGOPTIONS=--var=val" before starting the app, etc. As submitted,
    the plugin patch envisions defining a custom GUC variable for each PL and
    having each PL add logic to force loading of any shared library mentioned
    in its specific variable. I claim however that that is just duplicative,
    and that a single backend-wide GUC variable should be sufficient.

    Details
    -------

    I propose adding one function to dfmgr.c,

    void ** find_rendezvous_variable(const char *varname)

    Internally this function has a per-backend hashtable that associates names
    with "void *" data fields. It merely looks up the given name and returns
    a pointer to the data field; if the name is not already present then it's
    added with a data field initialized to NULL. The hashtable entries
    continue to exist for the life of the backend, and are never modified by
    the core backend code.

    A plugin such as a plpgsql debugger would do this in its _PG_init()
    function:

    static PLpgSQL_plugin my_plugin = { ... function addresses ... };

    PLpgSQL_plugin **var_ptr;

    var_ptr = (PLpgSQL_plugin **) find_rendezvous_variable("PLpgSQL_plugin");
    *var_ptr = &my_plugin;

    and this in its _PG_fini() function:

    PLpgSQL_plugin **var_ptr;

    var_ptr = (PLpgSQL_plugin **) find_rendezvous_variable("PLpgSQL_plugin");
    *var_ptr = NULL;

    Meanwhile, plpgsql itself would do this in its _PG_init() function:

    static PLpgSQL_plugin **plugin_ptr = NULL;

    plugin_ptr = (PLpgSQL_plugin **) find_rendezvous_variable("PLpgSQL_plugin");

    and in the places where it wants to pass control to the plugin, it'd do

    if (*plugin_ptr)
    ((*plugin_ptr)->function_field) (... args ...);

    The principal difference between this proposal and the original patch
    is that this way supports unloading of PL plugins; AFAICS, the original
    patch would just crash if the plugin were unloaded and then use of plpgsql
    continued. Also, this way doesn't depend on the user to correctly specify
    an initialization function within the plugin: as long as you load the
    right shared library, everything works.


    As for forcing the library load to occur, I propose a new GUC variable
    "backend_load_libraries" that is much like the postmaster's
    preload_libraries, except that the requested library loads happen
    at backend start time instead of in the postmaster. Then we need
    write and document the code only once, and there are other possible
    uses for it besides PL plugins.

    We need to think about security issues in defining such a variable:
    we don't want unprivileged users to be able to load arbitrary code
    into the server. One solution to this is to make the variable SUSET,
    ie, you must be superuser to set it. This would make it impossible
    for people to debug their own functions without superuser privileges
    ... but IIRC actual use of the proposed plpgsql debugger requires
    superuser privileges too, so this isn't necessarily a fatal objection.
    Still, it'd be nice if the PGOPTIONS way of setting the variable could
    be used without requiring that the client app itself run as superuser.
    Plan B is to restrict which shared libraries can be loaded using the
    variable --- there are different ways we could do that, but my suggestion
    would be to insist that the shared library come from "$libdir/plugins/".
    The DBA is then responsible for allowing only "safe" shared libraries
    to be installed in that directory, and therefore we can allow unprivileged
    users to set "backend_load_libraries". (We might as well also allow them
    to execute LOAD for these libraries, so that plugins could be switched
    intra-session without superuser privileges.)

    BTW, is anyone up for renaming the existing "preload_libraries" variable
    to "postmaster_load_libraries"? This would be more symmetrical with
    "backend_load_libraries", and so perhaps clearer about which does what
    when.

    Comments?

    regards, tom lane
  • Andreas Pflug at Aug 9, 2006 at 5:28 pm

    Tom Lane wrote:
    The other, probably more controversial bit of functionality is that there
    needs to be a way to cause a backend to load a PL plugin shared library
    without any cooperation from the connected client application. For
    interactive use of a PL debugger it might be sufficient to tell people to
    do "LOAD 'plpgsql_debugger'" before running their function-to-be-tested,
    but if you're trying to debug some behavior that only manifests in a large
    complicated application, it may be impractical to get the application to
    issue such a command.
    A similar issue applies to plain SQL that's not touching any PL: In the
    past, I encountered numerous situations where I'd have liked to take a
    peek at the current application's queries (on MSSQL, this can be done
    with SQL Profiler), but not have constant statement logging. IMHO it
    would be a good idea if

    - debugging could be turned on and off on-the-fly, e.g. to skip the app
    startup phase. Thus I question the statement "GUC variable is sufficient"
    - the mechnism would cover plain SQL too.

    Regards,
    Andreas
  • Tom Lane at Aug 9, 2006 at 8:04 pm

    Andreas Pflug writes:
    Tom Lane wrote:
    The other, probably more controversial bit of functionality is that there
    needs to be a way to cause a backend to load a PL plugin shared library
    without any cooperation from the connected client application.
    A similar issue applies to plain SQL that's not touching any PL: In the
    past, I encountered numerous situations where I'd have liked to take a
    peek at the current application's queries (on MSSQL, this can be done
    with SQL Profiler), but not have constant statement logging. IMHO it
    would be a good idea if
    - debugging could be turned on and off on-the-fly, e.g. to skip the app
    startup phase. Thus I question the statement "GUC variable is sufficient"
    - the mechnism would cover plain SQL too.
    I'd turn that around: I think you are arguing for a way to change GUC
    settings on-the-fly for a single existing session, without cooperation
    from the client. You can do that now if you're desperate enough (change
    postgresql.conf, SIGHUP just that backend, revert postgresql.conf
    change) but I agree something easier would be nice. In any case the
    problem needs a generic solution not something that only works for PL
    plugin loading, so solving it within GUC seems right to me.

    regards, tom lane
  • Andreas Pflug at Aug 9, 2006 at 8:47 pm

    Tom Lane wrote:
    I'd turn that around: I think you are arguing for a way to change GUC
    settings on-the-fly for a single existing session, without cooperation
    from the client.
    Ok, implemented that way would solve it (partially)
    Something like pg_set_guc(pid int4, varname text, value text) would be
    fine to set GUC on-the-fly. Could probably be signaled to the target
    backend with SIGHUP, but how should the individual parameter be
    transmitted, and eventually be retrieved? What about multiple parameters
    to be set atomically?

    A different aproach: A system table pg_guc, that holds current GUC
    settings for each backend.
    - on SIGHUP, the backend reload postgresql.conf as usual and writes guc
    into pg_guc, unless a "config file override" flag is set.
    - if pg_guc.config_override is set, guc are read from the table instead,
    and the flag is reset.
    - truncate pg_guc on postmaster start/restart

    Regards,
    Andreas

    PS the non-solved part for me is still that log_statement logging would
    still go to the standard log, in a less machine-readable way, mixed with
    other backend's data and possibly truncated. But that's a different story.
  • Jeff Davis at Aug 9, 2006 at 6:18 pm

    On Wed, 2006-08-09 at 12:44 -0400, Tom Lane wrote:
    A plugin such as a plpgsql debugger would do this in its _PG_init()
    function:

    static PLpgSQL_plugin my_plugin = { ... function addresses ... };

    PLpgSQL_plugin **var_ptr;

    var_ptr = (PLpgSQL_plugin **) find_rendezvous_variable("PLpgSQL_plugin");
    *var_ptr = &my_plugin;

    and this in its _PG_fini() function:

    PLpgSQL_plugin **var_ptr;

    var_ptr = (PLpgSQL_plugin **) find_rendezvous_variable("PLpgSQL_plugin");
    *var_ptr = NULL;

    Meanwhile, plpgsql itself would do this in its _PG_init() function:

    static PLpgSQL_plugin **plugin_ptr = NULL;

    plugin_ptr = (PLpgSQL_plugin **) find_rendezvous_variable("PLpgSQL_plugin");

    and in the places where it wants to pass control to the plugin, it'd do

    if (*plugin_ptr)
    ((*plugin_ptr)->function_field) (... args ...);
    I know this is a trivial question, but is there some kind of lock that
    would prevent the PG_fini for the plpgsql debugger from executing after
    "if(*plugin_ptr)" and before "((*plugin_ptr)->function_field)(...)"?

    Regards,
    Jeff Davis
  • Tom Lane at Aug 9, 2006 at 6:27 pm

    Jeff Davis writes:
    I know this is a trivial question, but is there some kind of lock that
    would prevent the PG_fini for the plpgsql debugger from executing after
    "if(*plugin_ptr)" and before "((*plugin_ptr)->function_field)(...)"?
    Backends are not multi-threaded.

    regards, tom lane
  • Korryd at Aug 9, 2006 at 9:25 pm

    ISTM there are two separate bits of functionality that the core backend
    needs to provide in support of PL plugins. The first is that we need a
    "rendezvous" facility whereby two separately-loaded shared libraries can
    connect and exchange data (a struct of function pointers for the immediate
    plans for plpgsql, but in general it might be anything). The exchanged
    data mustn't be limited to things known in advance to the core backend.
    The facility should support loading of communicating libraries in either
    order, and it should also allow for unloading of libraries. This seems
    easy enough to design: the core backend should basically provide a
    hashtable that maps names to "void *" pointer variables, and then two
    libraries that want to communicate just agree on a name and the data
    structure to be pointed to. (More details below.)

    I like it so far...

    The other, probably more controversial bit of functionality is that there
    needs to be a way to cause a backend to load a PL plugin shared library
    without any cooperation from the connected client application. For
    interactive use of a PL debugger it might be sufficient to tell people to
    do "LOAD 'plpgsql_debugger'" before running their function-to-be-tested,
    but if you're trying to debug some behavior that only manifests in a large
    complicated application, it may be impractical to get the application to
    issue such a command.

    Ok, but you should know that the PL/pgSQL debugger already handles this
    without any cooperation from the client.

    Loading the PL debugger means that your backend becomes debuggable, not
    that it actually starts debugging.

    If you want to debug a PL/pgSQL function invoked by some other process
    (such as a Web server), you create a "global breakpoint". When a
    debuggable process (that is, a process that has loaded the debugger
    plugin) trips across the breakpoint, that's when it starts debugging.
    (Note: a global breakpoint can identify a particular backend, by process
    ID, or it can omit the process ID and trap the first debuggable backend
    that trips across the breakpoint).

    So, other than the (negligible) performance penalty, its safe to load
    the debugger plugin into every backend. (If you've loaded the debugger,
    the extra overhead is a single, lightweight-lock protected,
    shared-memory hash lookup for each PL function invocation).

    We agreed while discussing this at the PG
    Anniversary Conference that providing a GUC variable for this purpose is
    probably sufficient, as there are multiple ways that such a variable can
    be set on behalf of an application: ALTER USER SET, ALTER DATABASE SET,
    "export PGOPTIONS=--var=val" before starting the app, etc. As submitted,
    the plugin patch envisions defining a custom GUC variable for each PL and
    having each PL add logic to force loading of any shared library mentioned
    in its specific variable. I claim however that that is just duplicative,
    and that a single backend-wide GUC variable should be sufficient.

    Ok, so the rendevous variables replace the per-language GUC variables
    (from my patch). In effect, a GUC variable is something that a user
    would manage, a rendevous variable is something that two (or more)
    pieces of code manage.

    GUC variables are visible to the user, rendevous variables are visible
    to dynamically loaded libraries.

    Oh, and rendevous variables are insensitve to load order too.

    Nice design.

    The principal difference between this proposal and the original patch
    is that this way supports unloading of PL plugins; AFAICS, the original
    patch would just crash if the plugin were unloaded and then use of plpgsql
    continued.

    I don't think it could crash because there's no way to unload a plugin
    (there is no UNLOAD statement, is there?).

    Which reminds me, you haven't proposed a way to unload a shared-library.

    We need to think about security issues in defining such a variable:
    we don't want unprivileged users to be able to load arbitrary code
    into the server. One solution to this is to make the variable SUSET,
    ie, you must be superuser to set it. This would make it impossible
    for people to debug their own functions without superuser privileges
    ... but IIRC actual use of the proposed plpgsql debugger requires
    superuser privileges too, so this isn't necessarily a fatal objection.

    Correct (the debugger currently requires superuser privileges). We'll
    probably want to relax that later.

    Still, it'd be nice if the PGOPTIONS way of setting the variable could
    be used without requiring that the client app itself run as superuser.
    Plan B is to restrict which shared libraries can be loaded using the
    variable --- there are different ways we could do that, but my suggestion
    would be to insist that the shared library come from "$libdir/plugins/".
    The DBA is then responsible for allowing only "safe" shared libraries
    to be installed in that directory, and therefore we can allow unprivileged
    users to set "backend_load_libraries". (We might as well also allow them
    to execute LOAD for these libraries, so that plugins could be switched
    intra-session without superuser privileges.)

    How about a combination of plan A and plan B? Make
    backend_load_libraries a USERSET variable, but you can't *add* libraries
    outside of $libdir/plugins/ unless you are a superuser.

    BTW, is anyone up for renaming the existing "preload_libraries" variable
    to "postmaster_load_libraries"? This would be more symmetrical with
    "backend_load_libraries", and so perhaps clearer about which does what

    Makes sense to me, of course that breaks existing postgresql.conf files.

    Do you want me to do any of this coding?


    --
    Korry Douglas korryd@enterprisedb.com
    EnterpriseDB http://www.enterprisedb.com
  • Tom Lane at Aug 9, 2006 at 10:05 pm

    "korryd@enterprisedb.com" <korryd@enterprisedb.com> writes:
    The other, probably more controversial bit of functionality is that there
    needs to be a way to cause a backend to load a PL plugin shared library
    without any cooperation from the connected client application.
    Ok, but you should know that the PL/pgSQL debugger already handles this
    without any cooperation from the client.
    Loading the PL debugger means that your backend becomes debuggable, not
    that it actually starts debugging.
    Right, the question is how do you load it, assuming that you do not want
    to enable it for every single session in your database.
    So, other than the (negligible) performance penalty, its safe to load
    the debugger plugin into every backend. (If you've loaded the debugger,
    the extra overhead is a single, lightweight-lock protected,
    shared-memory hash lookup for each PL function invocation).
    I'm not sure you'll be able to convince everyone that the penalty is so
    negligible --- any high-rate access to shared memory is potentially very
    expensive, see nearby threads for examples. Even if this is affordable
    for the debugger, what of more-invasive plugins such as the performance
    monitor? I think a credible general-purpose plugin design has to
    address the problem of enabling plugins on-the-fly.
    I don't think it could crash because there's no way to unload a plugin
    (there is no UNLOAD statement, is there?).
    What we actually have at the moment is that you can LOAD a library
    again, which causes an unload of the prior version and then loading the
    new. I suppose this feature was intended to speed library development by
    letting you recompile and then update into your existing backend session.
    Not sure how many people are using it, but it's there ...
    Which reminds me, you haven't proposed a way to unload a shared-library.
    This depends on the semantics we want to assign to
    backend_shared_libraries --- I could imagine defining it as "if you
    remove an entry from the value then we'll unload that library".
    How about a combination of plan A and plan B? Make
    backend_load_libraries a USERSET variable, but you can't *add* libraries
    outside of $libdir/plugins/ unless you are a superuser.
    Not sure how easy that is (ie, can we track which part of the list came
    from where), but if doable it'd be OK with me. We might have to split
    it into two list variables to make it work, and I'm not sure it's worth
    the complication.
    BTW, is anyone up for renaming the existing "preload_libraries" variable
    to "postmaster_load_libraries"? This would be more symmetrical with
    "backend_load_libraries", and so perhaps clearer about which does what
    Makes sense to me, of course that breaks existing postgresql.conf files.
    We already broke them by removing the init-function name...
    Do you want me to do any of this coding?
    Up to you --- I can do it if you don't want to.

    regards, tom lane
  • Korryd at Aug 9, 2006 at 10:43 pm

    I'm not sure you'll be able to convince everyone that the penalty is so
    negligible --- any high-rate access to shared memory is potentially very
    expensive, see nearby threads for examples. Even if this is affordable
    for the debugger, what of more-invasive plugins such as the performance
    monitor? I think a credible general-purpose plugin design has to
    address the problem of enabling plugins on-the-fly.

    I have no problem with your solution - I think its a very nice design.

    I don't think it could crash because there's no way to unload a plugin
    (there is no UNLOAD statement, is there?).
    What we actually have at the moment is that you can LOAD a library
    again, which causes an unload of the prior version and then loading the
    new. I suppose this feature was intended to speed library development by
    letting you recompile and then update into your existing backend session.
    Not sure how many people are using it, but it's there ...

    Right, but you still end up with a plugin loaded afterwards so no crash
    (of course you could do something stupid like load a new plugin with the
    same name that isn't really a plugin).

    Which reminds me, you haven't proposed a way to unload a shared-library.
    This depends on the semantics we want to assign to
    backend_shared_libraries --- I could imagine defining it as "if you
    remove an entry from the value then we'll unload that library".

    That's what I was thinking too.

    How about a combination of plan A and plan B? Make
    backend_load_libraries a USERSET variable, but you can't *add* libraries
    outside of $libdir/plugins/ unless you are a superuser.
    Not sure how easy that is (ie, can we track which part of the list came
    from where), but if doable it'd be OK with me. We might have to split
    it into two list variables to make it work, and I'm not sure it's worth
    the complication.

    The GUC assign hook would parse through backend_load_libraries...

    for each library,
    {
    if ( the library is already loaded )
    {
    // it's not a new library, doesn't matter where it lives,
    doesn't matter if we're a superuser

    load( library)
    }
    else
    {
    // it's a new entry in backed_load_libraries

    if( library lives in $libdir/plugins )
    load( library )
    else
    {
    if( is_superuser())
    load( library )
    else
    throw an error
    }
    }
    }

    We already broke them by removing the init-function name...

    Right...

    Do you want me to do any of this coding?
    Up to you --- I can do it if you don't want to.

    I'll take a stab at it... thanks for your help so far.

    -- Korry



    --
    Korry Douglas korryd@enterprisedb.com
    EnterpriseDB http://www.enterprisedb.com
  • Tom Lane at Aug 9, 2006 at 11:05 pm

    "korryd@enterprisedb.com" <korryd@enterprisedb.com> writes:
    (there is no UNLOAD statement, is there?).
    What we actually have at the moment is that you can LOAD a library
    again, which causes an unload of the prior version and then loading the
    new.
    Right, but you still end up with a plugin loaded afterwards so no crash
    (of course you could do something stupid like load a new plugin with the
    same name that isn't really a plugin).
    That is only true given careful design and implementation of the
    hooks. Right now for instance I think it's possible to crash the
    backend by doing "LOAD 'plpgsql'" multiple times, because it hooks
    into CallXactCallbacks and doesn't unhook. (Now that we have PG_fini
    it should be possible to fix that...) Doesn't seem to crash
    on the HPUX machine I just tried it on, but maybe HPUX is weird and
    doesn't actually remove the old library from the address space?

    Anyway I disagree with your proposal to let unprivileged users re-LOAD
    random libraries. If they've not been modified to have clean unload
    semantics this isn't safe.

    regards, tom lane
  • Simon Riggs at Aug 10, 2006 at 6:45 am

    On Wed, 2006-08-09 at 18:04 -0400, Tom Lane wrote:
    BTW, is anyone up for renaming the existing "preload_libraries"
    variable
    to "postmaster_load_libraries"? This would be more symmetrical
    with
    "backend_load_libraries", and so perhaps clearer about which does
    what
    Makes sense to me, of course that breaks existing postgresql.conf
    files.

    We already broke them by removing the init-function name...
    How about:

    shared_load_libraries (rather than postmaster_load_libraries)
    local_load_libraries (rather than backend_load_libraries)

    which is more informative for people that don't know/care what a
    postmaster or a backend is and what implications those phrases carry.

    --
    Simon Riggs
    EnterpriseDB http://www.enterprisedb.com
  • Korryd at Aug 10, 2006 at 3:55 pm

    As for forcing the library load to occur, I propose a new GUC variable
    "backend_load_libraries" that is much like the postmaster's
    preload_libraries, except that the requested library loads happen
    at backend start time instead of in the postmaster. Then we need
    write and document the code only once, and there are other possible
    uses for it besides PL plugins.

    Any thoughts about where to put the call to process_backend_libraries()
    (the new function to handle backend_load_libraries)?

    I'm thinking that it should go in PostgresMain(), just after (before?)
    the call to BeginReportingGUCOptions() - by that time, we know whether
    we are a superuser and we have processed all GUC options.

    Also, should we create an on_proc_exit() handler that would unload all
    dynamic libraries (specifically to call the _PG_fini() functions)?

    -- Korry


    --
    Korry Douglas korryd@enterprisedb.com
    EnterpriseDB http://www.enterprisedb.com
  • Tom Lane at Aug 10, 2006 at 4:05 pm

    "korryd@enterprisedb.com" <korryd@enterprisedb.com> writes:
    Any thoughts about where to put the call to process_backend_libraries()
    (the new function to handle backend_load_libraries)?
    I'm thinking that it should go in PostgresMain(), just after (before?)
    the call to BeginReportingGUCOptions() - by that time, we know whether
    we are a superuser and we have processed all GUC options.
    Sounds fine.
    Also, should we create an on_proc_exit() handler that would unload all
    dynamic libraries (specifically to call the _PG_fini() functions)?
    Yeah, I thought about that too, but I'm inclined not to do it;
    it seems like just excess cycles. The process is quitting anyway,
    so the only reason this would be useful is if the library thinks it's
    going to update external or shared state during _PG_fini ... and on
    the whole that sounds like a bad idea. Besides, if a library really
    needs this it can add its own on_proc_exit handler.

    regards, tom lane
  • Korryd at Aug 10, 2006 at 11:03 pm

    Also, should we create an on_proc_exit() handler that would unload all
    dynamic libraries (specifically to call the _PG_fini() functions)?
    Yeah, I thought about that too, but I'm inclined not to do it;
    it seems like just excess cycles. The process is quitting anyway,
    so the only reason this would be useful is if the library thinks it's
    going to update external or shared state during _PG_fini ... and on
    the whole that sounds like a bad idea. Besides, if a library really
    needs this it can add its own on_proc_exit handler.

    It seems a little dangerous for a dynamic library to register an
    on_proc_exit() handler. If we ever add support for unloading a dynamic
    library, we'll have to add an unregister_on_proc_exit() too. Otherwise,
    a dynamic library might register a function pointer with on_proc_exit()
    and then leave a dangling pointer when it gets unloaded.

    Given that, I assume you don't feel the need to unload old shared
    libraries if the user (a superuser) removes an entry from
    backend_load_libraries, right?

    In fact, it looks _PG_fini() is only called if you *reload* a library,
    unless I'm missing something somwhere.


    --
    Korry Douglas korryd@enterprisedb.com
    EnterpriseDB http://www.enterprisedb.com
  • Tom Lane at Aug 11, 2006 at 12:17 am

    "korryd@enterprisedb.com" <korryd@enterprisedb.com> writes:
    It seems a little dangerous for a dynamic library to register an
    on_proc_exit() handler. If we ever add support for unloading a dynamic
    library, we'll have to add an unregister_on_proc_exit() too.
    True, but there might be other uses for such a thing anyway. I can't
    see any objection to adding that routine.
    In fact, it looks _PG_fini() is only called if you *reload* a library,
    unless I'm missing something somwhere.
    Sure, because we don't currently have a routine for unloading a library
    without immediately reloading it.

    regards, tom lane

Related Discussions

Discussion Navigation
viewthread | post
Discussion Overview
grouppgsql-hackers @
categoriespostgresql
postedAug 8, '06 at 5:26p
activeAug 11, '06 at 12:17a
posts17
users5
websitepostgresql.org...
irc#postgresql

People

Translate

site design / logo © 2022 Grokbase