Thread: queriing the version of libpq

On Tue, Oct 5, 2010 at 09:33, Massa, Harald Armin <chef@ghum.de> wrote:
> With 9.0 there is the new hex encoding for BYTEA, which is activated by
> default.
> libpq BEFORE 9.0 are not able to decode that encoding.
> I am programming with Python, using psycopg2. When psycopg2 is linked with
> libpq 9.0, everything works fine with hex-encoding; if psycopg2 is linked
> with libpq < 9.0, decoding hex-encoded bytea fails (it stays hexencoded).
> This happens because in default configuration psycopg2 calls the
> libpq-decode-encoded-bytea function (which is the way it should be done).
> Now I would love to have an additional check "is the used psycopg2 linked to
> an advanced-enough libpq", to be able to set bytea_output to 'escape' if the
> libpq is not worthy.
> My question: Which way is available to query the linked libpq version?
> My other option is to select 'something_that_gets_casted_to_bytea'::bytea,
> and check the return value. BUT that requires a round-trip to the server....

You can try calling PQconninfoParse() on a connectino string that has
applicationname= in it. That will fail on anything pre-9.0. Assuming
there's a way to access that function through psycopg2.

But it does outline that fact that it wouldn't suck to have a function
in libpq returning the version so that application can check this at
runtime - clearly it would also be useful when being linked "through"
something like psycopg2.

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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> My question: Which way is available to query the linked libpq version?

That's information your driver should be supplying. For example, in
Perl (DBD::Pg), you would say

if ($dbh->{pg_lib_version} >= 90000) {

I'd raise a bug with psycopg2 if it does not provide that information.

- --
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On Tue, Oct 5, 2010 at 16:32, Greg Sabino Mullane <greg@turnstep.com> wrote:
>> My question: Which way is available to query the linked libpq version?
>
> That's information your driver should be supplying. For example, in
> Perl (DBD::Pg), you would say
>
> if ($dbh->{pg_lib_version} >= 90000) {
>
> I'd raise a bug with psycopg2 if it does not provide that information.

How does the driver figure it out?

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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>> if ($dbh->{pg_lib_version} >= 90000) {
>>
>> I'd raise a bug with psycopg2 if it does not provide that information.
>
> How does the driver figure it out?

DBD::Pg parses pg_config --version, then passes the information
to the C programs for directive fiddling. I certainly hope
other drivers are doing the same, as libpq varies across
major versions a good deal.

- --
Greg Sabino Mullane greg@turnstep.com
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On 5 October 2010 16:33, Greg Sabino Mullane <greg@turnstep.com> wrote:
>
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>
>
>>> if ($dbh->{pg_lib_version} >= 90000) {
>>>
>>> I'd raise a bug with psycopg2 if it does not provide that information.
>>
>> How does the driver figure it out?
>
> DBD::Pg parses pg_config --version, then passes the information
> to the C programs for directive fiddling. I certainly hope
> other drivers are doing the same, as libpq varies across
> major versions a good deal.

I would imagine that most libpq wrapping drivers use libpq's
PQserverVersion(), which returns an integer that looks like 90000.


--
Regards,
Peter Geoghegan

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> I would imagine that most libpq wrapping drivers use libpq's
> PQserverVersion(), which returns an integer that looks like 90000.

Yeah, I'm familiar with that (I wrote it :) but it's not useful
here for two reasons:

1) It's not available on older versions

2) It returns the *target* version, not the *compiled* version.
In other words, it requires an existing PGconn object.

- --
Greg Sabino Mullane greg@turnstep.com
End Point Corporation http://www.endpoint.com/
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Peter Geoghegan <peter.geoghegan86@gmail.com> writes:
> On 5 October 2010 16:33, Greg Sabino Mullane <greg@turnstep.com> wrote:
>>> How does the driver figure it out?
>>
>> DBD::Pg parses pg_config --version, then passes the information
>> to the C programs for directive fiddling. I certainly hope
>> other drivers are doing the same, as libpq varies across
>> major versions a good deal.

> I would imagine that most libpq wrapping drivers use libpq's
> PQserverVersion(), which returns an integer that looks like 90000.

The real problem is that neither of these can be trusted to tell you the
*library* version.  PQserverVersion() is something else altogether,
and I wouldn't want to assume that pg_config exactly matches the library
you're linked to --- if it's even present at all.

We could add a PQlibpqVersion(), maybe, but it would be many years
before client code could rely on that being present.

            regards, tom lane

On Tue, Oct 5, 2010 at 18:41, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Peter Geoghegan <peter.geoghegan86@gmail.com> writes:
>> On 5 October 2010 16:33, Greg Sabino Mullane <greg@turnstep.com> wrote:
>>>> How does the driver figure it out?
>>>
>>> DBD::Pg parses pg_config --version, then passes the information
>>> to the C programs for directive fiddling. I certainly hope
>>> other drivers are doing the same, as libpq varies across
>>> major versions a good deal.
>
>> I would imagine that most libpq wrapping drivers use libpq's
>> PQserverVersion(), which returns an integer that looks like 90000.
>
> The real problem is that neither of these can be trusted to tell you the
> *library* version.  PQserverVersion() is something else altogether,
> and I wouldn't want to assume that pg_config exactly matches the library
> you're linked to --- if it's even present at all.
>
> We could add a PQlibpqVersion(), maybe, but it would be many years
> before client code could rely on that being present.

I think we should.

And in a small way they can already - if they check for it
dynamically, they'll know if it was 9.1 or newer at least :-) It'll be
a long time before it's *easy* to use though. But if we don't add it
now, it'll be even longer...

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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> The real problem is that neither of these can be trusted to tell you the
> *library* version.  PQserverVersion() is something else altogether,
> and I wouldn't want to assume that pg_config exactly matches the library
> you're linked to --- if it's even present at all.

Er...yes it will match exact...because we[1] get the location of the
library files from pg_config as well. :) Handy little utility that.

[1] DBD::Pg


- --
Greg Sabino Mullane greg@turnstep.com
End Point Corporation http://www.endpoint.com/
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On Tue, Oct 5, 2010 at 22:39, Greg Sabino Mullane <greg@turnstep.com> wrote:
>
>
>> The real problem is that neither of these can be trusted to tell you the
>> *library* version.  PQserverVersion() is something else altogether,
>> and I wouldn't want to assume that pg_config exactly matches the library
>> you're linked to --- if it's even present at all.
>
> Er...yes it will match exact...because we[1] get the location of the
> library files from pg_config as well. :) Handy little utility that.

How do you get pg_config to tell you which of the multiple versions of
libpq that may be installed on the machine you are actually linking
against?

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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>> Er...yes it will match exact...because we[1] get the location of the
>> library files from pg_config as well. :) Handy little utility that.
>
> How do you get pg_config to tell you which of the multiple versions of
> libpq that may be installed on the machine you are actually linking
> against?

Not sure what you mean. pg_config *drives* the compilation and linking,
we don't blindly compile and simply take pg_config's word for it.
pg_config --libdir and pg_config --includedir.

- --
Greg Sabino Mullane greg@turnstep.com
End Point Corporation http://www.endpoint.com/
PGP Key: 0x14964AC8 201010051651
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"Greg Sabino Mullane" <greg@turnstep.com> writes:
>> The real problem is that neither of these can be trusted to tell you the
>> *library* version.  PQserverVersion() is something else altogether,
>> and I wouldn't want to assume that pg_config exactly matches the library
>> you're linked to --- if it's even present at all.

> Er...yes it will match exact...because we[1] get the location of the
> library files from pg_config as well. :) Handy little utility that.

[ shrug... ]  It's not at all hard to think of scenarios where that will
give you misleading results, even granted that you're willing to fall
over when pg_config isn't present.  But regardless of that, the
technique simply isn't available to ordinary C code using the standard
dynamic linker.

            regards, tom lane

On Tue, Oct 5, 2010 at 22:53, Greg Sabino Mullane <greg@turnstep.com> wrote:
>
>>> Er...yes it will match exact...because we[1] get the location of the
>>> library files from pg_config as well. :) Handy little utility that.
>>
>> How do you get pg_config to tell you which of the multiple versions of
>> libpq that may be installed on the machine you are actually linking
>> against?
>
> Not sure what you mean. pg_config *drives* the compilation and linking,
> we don't blindly compile and simply take pg_config's word for it.
> pg_config --libdir and pg_config --includedir.

But that's build-time, not run-time.

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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> Not sure what you mean. pg_config *drives* the compilation and linking,
> we don't blindly compile and simply take pg_config's word for it.
> pg_config --libdir and pg_config --includedir.

> But that's build-time, not run-time.

Correct, not sure of your point. Is this a problem? Build-time is
what we want here (determining the libpq we were built with)

- --
Greg Sabino Mullane greg@turnstep.com
End Point Corporation http://www.endpoint.com/
PGP Key: 0x14964AC8 201010060816
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On Wed, Oct 6, 2010 at 14:17, Greg Sabino Mullane <greg@turnstep.com> wrote:
>
>
>> Not sure what you mean. pg_config *drives* the compilation and linking,
>> we don't blindly compile and simply take pg_config's word for it.
>> pg_config --libdir and pg_config --includedir.
>
>> But that's build-time, not run-time.
>
> Correct, not sure of your point. Is this a problem? Build-time is
> what we want here (determining the libpq we were built with)

The original question was how to find this out from python, which
means at runtime.

And the pg_lib_version of DBD::Pg clearly doesn't tell you what
version of libpq it's using, only what it was built against.

As long as you have libpq 9.0, you can decode the bytea hex thingy,
irregardless of what version of libpq your <whatever other
code/library> was linked against.

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

Magnus Hagander <magnus@hagander.net> writes:
> On Wed, Oct 6, 2010 at 14:17, Greg Sabino Mullane <greg@turnstep.com> wrote:
>>> But that's build-time, not run-time.
>>
>> Correct, not sure of your point. Is this a problem? Build-time is
>> what we want here (determining the libpq we were built with)

> The original question was how to find this out from python, which
> means at runtime.

> And the pg_lib_version of DBD::Pg clearly doesn't tell you what
> version of libpq it's using, only what it was built against.

> As long as you have libpq 9.0, you can decode the bytea hex thingy,
> irregardless of what version of libpq your <whatever other
> code/library> was linked against.

The problem here is that you might actually be *running* with a
different version of libpq than you built against.  This is actually
highly likely if you distribute an executable that dynamically links
to a shared library at runtime.  And the dynamic linker will take any
version of libpq.so that has the same major number, meaning that you
cannot assume that it's not 8.4 just because you built against 9.0.

            regards, tom lane

On Wed, Oct 6, 2010 at 15:54, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Magnus Hagander <magnus@hagander.net> writes:
>> On Wed, Oct 6, 2010 at 14:17, Greg Sabino Mullane <greg@turnstep.com> wrote:
>>>> But that's build-time, not run-time.
>>>
>>> Correct, not sure of your point. Is this a problem? Build-time is
>>> what we want here (determining the libpq we were built with)
>
>> The original question was how to find this out from python, which
>> means at runtime.
>
>> And the pg_lib_version of DBD::Pg clearly doesn't tell you what
>> version of libpq it's using, only what it was built against.
>
>> As long as you have libpq 9.0, you can decode the bytea hex thingy,
>> irregardless of what version of libpq your <whatever other
>> code/library> was linked against.
>
> The problem here is that you might actually be *running* with a
> different version of libpq than you built against.  This is actually
> highly likely if you distribute an executable that dynamically links
> to a shared library at runtime.  And the dynamic linker will take any
> version of libpq.so that has the same major number, meaning that you
> cannot assume that it's not 8.4 just because you built against 9.0.

Uh, that's what I was saying. The build version is quite irrelevant for that.

Not to mention when you're on windows (and I dunno if any other
platforms are like *that*), where they're all  libpq.dll and we'll
happily take *any* other libpq.dll (even an older one, but that will
give you an error if you're actually using any functions not present
in it).


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On tis, 2010-10-05 at 09:33 +0200, Massa, Harald Armin wrote:
> Now I would love to have an additional check "is the used psycopg2
> linked to an advanced-enough libpq", to be able to set bytea_output to
> 'escape' if the libpq is not worthy.

This is really something that psycopg2 should work out for you.  I
suggest you take up a discussion on this on their mailing list.

On Thu, 2010-10-07 at 12:23 +0300, Peter Eisentraut wrote:
> This is really something that psycopg2 should work out for you.  I
> suggest you take up a discussion on this on their mailing list.

...which is down over the last 3 weeks or so:

http://www.initd.org/

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On Oct 7, 2010, at 5:34 AM, Devrim GÜNDÜZ wrote:

> On Thu, 2010-10-07 at 12:23 +0300, Peter Eisentraut wrote:
>> This is really something that psycopg2 should work out for you.  I
>> suggest you take up a discussion on this on their mailing list.
>
> ...which is down over the last 3 weeks or so:
>
> http://www.initd.org/

In addition, I posted a patch for 9.0 support which was supposed to be rolled in to psycopg2 weeks ago. Now I am stuck
pushingmy own psycopg2 egg around. The psycopg2 project is too reliant on one person (who has trouble managing his
servers)-I wish he would move the project to a public project management service. 

I also remember a discussion on the poor state of postgresql drivers for python and which driver the PostgreSQL project
shouldendorse- it looks like the situation has not improved. Here's the thread:
http://archives.postgresql.org/pgsql-hackers/2010-02/msg00351.php

Cheers,
M

A.M. wrote:
>
> On Oct 7, 2010, at 5:34 AM, Devrim G?ND?Z wrote:
>
> > On Thu, 2010-10-07 at 12:23 +0300, Peter Eisentraut wrote:
> >> This is really something that psycopg2 should work out for you.  I
> >> suggest you take up a discussion on this on their mailing list.
> >
> > ...which is down over the last 3 weeks or so:
> >
> > http://www.initd.org/
>
> In addition, I posted a patch for 9.0 support which was supposed to be
> rolled in to psycopg2 weeks ago. Now I am stuck pushing my own psycopg2
> egg around. The psycopg2 project is too reliant on one person (who has
> trouble managing his servers)- I wish he would move the project to a
> public project management service.
>
> I also remember a discussion on the poor state of postgresql drivers
> for python and which driver the PostgreSQL project should endorse- it
> looks like the situation has not improved. Here's the thread:
> http://archives.postgresql.org/pgsql-hackers/2010-02/msg00351.php

The python driver situation did improve, for a while.  :-|

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +

>> My question: Which way is available to query the linked libpq version?

> But it does outline that fact that it wouldn't suck to have a >function  in libpq returning the version so that
applicationcan >check this at  runtime - clearly it would also be useful when >being linked "through" something like
psycopg2.

did there something happen?

happen as in "an addition of a function to libpq to query its version
without a server roundtrip AFTER libpq has been linked into sth has
been decided for / against"

Harald


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Amtsgericht Stuttgart, HRB 734971
-
persuadere.
et programmare

#include <pg_config.h>

/usr/include/pg_config-x86_64.h:#define PG_VERSION "9.6.9"
/usr/include/pg_config-x86_64.h:#define PG_VERSION_NUM 90609
/usr/include/pg_config-x86_64.h:#define PG_VERSION_STR "PostgreSQL 9.6.9 on
x86_64-redhat-linux-gnu, compiled by gcc (GCC) 7.3.1 20180303 (Red Hat
7.3.1-5), 64-bit"

I also have source for 8.4 and its there too.



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