| CC: | dbd-pg [...] perl.org |
| Subject: | DBD::Pg not thread safe ? |
| Date: | Sun, 21 Mar 2010 10:22:45 +0100 (CET) |
| To: | bug-dbd-pg [...] rt.cpan.org |
| From: | Fabien COELHO <fabien.coelho [...] mines-paristech.fr> |
Hello bug-report automaton !
Hello maintainer !
I always run into segmentation faults when running two parallel database
connections in distinct threads. It is not new and was always true, it is
just that today I decided to write a bug report:-)
Version: DBI 1.609, DBD:Pg 2.13.1
Perl: v5.10.0 built for i486-linux-gnu-thread-multi
OS: Linux Ubuntu Karmic (9.10)
libpq: 8.4.2
With pg_comparator (http://www.coelho.net/pg_comparator) using the
-T (thread option). The script creates two threads which perform queries
in parallel on two distinct connections. This result in:
...
Can't call do method on handle DBI::db=HASH(0xb6c1a238) after take_imp_data() at ./pg_comparator line 789.
...
Use of uninitialized value in subroutine entry at ./pg_comparator line 789.
Segmentation fault
line 789 is : return $dbh->do($query);
query is (from the debug output, if I'm not mistaken about the thread) :
CREATE TEMPORARY TABLE cmp_2_1 AS
SELECT idc & 0 AS idc, xor(cks) AS cks
FROM cmp_2_0 GROUP BY idc & 0
Sorry, no time for a "minimal" or even "small" example... However you can
find attached a DBI level 10 trace with and without threads. Only the
threaded version does a segmentation fault.
Repeat: with pg_comparator (http://coelho.net/pg_comparator), load
extensions (see INSTALL) and then run on a table in a base by
substitutuing login, password, host, base, table, pkey, other, cols
according to your setting...
Show quoted text
sh> DBI_TRACE=10 pg_comparator -v -v -v -T \
login:password@host/base/table?pkey:other,cols \
login:password@host/base/table?pkey:other,cols
...
lots of stuff, see trace...
...
segmentation fault
Note that it works fine when the -T option is removed, so there is a
workaround which is not to use threads. Possibly the issue is in libpq
which may not be thread safe under some conditions, but this is not
expected. I tested:
Show quoted text sh> cat test.c
#include<stdio.h>
#include "libpq-fe.h"
int main(void) {
fprintf(stdout, "thread safety is %d\n", PQisthreadsafe());
return 0;
}
Show quoted text sh> gcc -I/usr/include/postgresql -lpq test.c
sh> ./a.out
thread safety is 1
--
Fabien COELHO.
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