queriing the version of libpq
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....
Harald
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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 ($dbh->{pg_lib_version} >= 90000) {
I'd raise a bug with psycopg2 if it does not provide that information.
- --
Greg Sabino Mullane greg@turnstep.com
PGP Key: 0x14964AC8 201010051030
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On Tue, Oct 5, 2010 at 16:32, Greg Sabino Mullane <greg@turnstep.com> wrote:
My question: Which way is available to query the linked libpq version?
That's information your driver should be supplying. For example, in
Perl (DBD::Pg), you would sayif ($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 ($dbh->{pg_lib_version} >= 90000) {
I'd raise a bug with psycopg2 if it does not provide that information.
How does the driver figure it out?
DBD::Pg parses pg_config --version, then passes the information
to the C programs for directive fiddling. I certainly hope
other drivers are doing the same, as libpq varies across
major versions a good deal.
- --
Greg Sabino Mullane greg@turnstep.com
PGP Key: 0x14964AC8 201010051132
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8
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On 5 October 2010 16:33, Greg Sabino Mullane <greg@turnstep.com> wrote:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: RIPEMD160if ($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/
PGP Key: 0x14964AC8 201010051212
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I would imagine that most libpq wrapping drivers use libpq's
PQserverVersion(), which returns an integer that looks like 90000.exactly that is exposed as cn.server_version property of the psycopg2
connection object; but it does not help, as a 8.4libpq happily connects to a
9.0 server... for some values of happy :)
Harald
--
GHUM GmbH
Harald Armin Massa
Spielberger Straße 49
70435 Stuttgart
0173/9409607
Amtsgericht Stuttgart, HRB 734971
-
persuadere.
et programmare
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/
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...
and an additional argument: Isn't it a wise decision for clients, to allways
use the newset libpq, independent of the server? As younger libpqs happily
connect to older servers AND are supposed to have less bugs.
As libpq is very small, can be statically linked into applications and there
are no license troubles, I can see no argument to use something that is not
brand new... (compared to other databases with 120megabyte clients with
longer licence restrictions than documentations...)
Or am I missing sth?
Harald
--
GHUM GmbH
Harald Armin Massa
Spielberger Straße 49
70435 Stuttgart
0173/9409607
Amtsgericht Stuttgart, HRB 734971
-
persuadere.
et programmare
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Hash: RIPEMD160
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]DBD::Pg 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/
PGP Key: 0x14964AC8 201010051638
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8
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Hey all,
Could you call it as PQlibVersion() or even PQversion() instead of
PQlibpqVersion() ?
2010/10/5 Tom Lane <tgl@sss.pgh.pa.us>
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
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// Dmitriy.
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
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8
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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/
-----BEGIN PGP SIGNED MESSAGE-----
Hash: RIPEMD160
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
http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8
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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
