Thread: General Bug Report: Large Object Example testlo fails

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                        POSTGRESQL BUG REPORT TEMPLATE
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Your name               : Mika Saari
Your email address      : Mika.Saari@nokia.com

Category                : runtime: front-end: C++
Severity                : non-critical

Summary: Large Object Example testlo fails

System Configuration
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  Operating System   : Linux 2.2.5 ELF

  PostgreSQL version : 6.5

  Compiler used      : egcs-2.91.66

Hardware:
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PII, 128MB RAM, 18Gb DISK
Linux <mymachine> 2.2.5-15 #1 Mon Apr 19 23:00:46 EDT 1999 unknown
RedHat 6.0

Versions of other tools:
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GNU Make version 3.77
Flex Version 2.5.4


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Problem Description:
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Large Object Example testlo fails in PostgreSQL 6.5 but NOT
in 6.4.2. The ERROR message is

  Connection to database 'template1' failed.
  PQsendQuery() -- There is no connection to the backend.


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Test Case:
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1. tar xvzf postgresql-6.5.tar.gz
2. cd postgresql-6.5
3. cd src
4. ./configure --prefix=/opt/postgresql-v6.5
5. make; make install
6. ldconfig
7. chown -R postgres /opt/postgresql-v6.5 /opt/postgresql-6.5
8. su - postgres
9. initdb
10.postmaster -i
11.cd /opt/postgresql-6.5/src/interfaces/libpq++/examples
12.vi Makefile
  HEADERDIR=/opt/postgresql-v6.5/include
  LIBPQDIR=/opt/postgresql-v6.5/lib
  LDFALGS+= -L$(LIBPQDIR) -lcrypt -lpq++
13. make
14. ./testlo template1 testlo test 0
  This command has been tested with all parameters world
  can handle ;)

All other example files libtestpq0 - libtestpq6 works
without any problem.

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Solution:
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Mika.Saari@nokia.com writes:
> libpq++ Large Object Example testlo fails in PostgreSQL 6.5 but NOT
> in 6.4.2. The ERROR message is
>   Connection to database 'template1' failed.
>   PQsendQuery() -- There is no connection to the backend.

> 14. ./testlo template1 testlo test 0

It looks like testlo is now set up so that the first argument is a
conninfo string, not just a database name.  So, something like

    ./testlo dbname=template1 testlo test 0

should work.

If the other method is still being recommended in some documentation
somewhere, then we need to fix that --- where did you find the info?

Also, I'd say that the error message here is pretty awful.  Looks like
that's because PQconnectdb's original message about bogus syntax for a
conninfo string (which might actually have been helpful) is being
overwritten when the PgLargeObject constructors plow ahead with trying
to create and open a large object.  They should not do that if the
underlying connection constructor failed :-(.

Finally, I don't particularly like the fact that both constructors for
PgLargeObject insist on creating and opening a LO.  If you're going to
import() or export() you do not need an LO filehandle; and if you're
going to import() then the constructor-created LO is wasted, making
for a semi-permanent diskspace leak.

Perhaps the best way to design PgLargeObject is to make both creation
and opening "lazy", happening only at the first call that requires 'em.

            regards, tom lane