There appears to be a bug in the code used by DBD::Pg's 'lo_read' function. I presume the code with the bug is a part of libpq, and thus the postgresql-libs RPM binary distribution.
The nature of the bug is that an 'lo_read' operation performed with DBD::Pg caused a segfault with postgresql-libs-7.3.2 and "hangs" on files >= 32768 bytes with postgresql-libs-7.3.4. The hang is actually a read() loop on the socket generating EAGAIN error on each read().
I've attached a short perl script that demonstrates the bug. The database server does not seem to matter; I get the same results using 7.2 as I do with 7.3.x servers. I also get the same results when I vary the perl-DBD-Pg and perl-DBI module versions. The bug seems to be following libpg.
All of my testing has been on the i686 platform using linux 2.4.20 kernels.
Test case #1:
- client = postgresql-libs-7.2.3-5 (redhat-7.3)
perl-DBI-1.21-1 (redhat-7.3)
perl-DBD-Pg-1.01-8 (redhat-7.3)
perl-5.6.1
- server = postgresql-server-7.3.2-3 (redhat-9)
- transport = tcpip + ssl$ perl test.pl - reading testfile '/bin/ls' - inserting testfile contents - oid = '16265435' - reading large object success.. removing large object
Test case #2:
- client = postgresql-libs-7.3.2-3 (redhat-9)
perl-DBI-1.32-5 (redhat-9)
perl-DBD-Pg-1.21-2 (redhat-9)
-server = postgresql-server-7.3.2-3 (redhat-9)
-transport = tcpip + ssl$ perl test.pl - reading testfile '/bin/ls' - inserting testfile contents - oid = '16265436' - reading large object Segmentation fault
... after ~32768 bytes, process loops reading the socket read(3, 0x81cc938, 5) = -1 EAGAIN (Resource temporarily unavailable) and eventually segfaults
Test case #3: - same as #2 except - transport = tcpip (localhost)
$ perl test.pl - reading testfile '/bin/ls' - inserting testfile contents - oid = '16265436' - reading large object Segmentation fault
Test case #4: - same as #2 and #3 except - postgresql-libs-7.3.4 PGDG used
$ perl test.pl - reading testfile '/bin/ls' - inserting testfile contents - oid = '16265437' - reading large object
... after ~32768 bytes, process loops reading the socket read(3, 0x81cc938, 5) = -1 EAGAIN (Resource temporarily unavailable) but doesn't appear to segfault (unless I am not patient enough)
This problem is a bastard as it makes getting data out of an otherwise perfectly good database rather difficult. In other words, its a show-stopper when migrating from 7.2 -> 7.3.
Regards, Kevin
test.pl
Description: Binary data
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