Unable to dump database/table

Hello.

pg_dump cann't dump some databases (at least one table) with the
following error ;

$ pg_dump -b -F c -v -f pgdump_void_2004-10-11T03:04:00 void
pg_dump: saving encoding
pg_dump: saving database definition
pg_dump: reading schemas
pg_dump: reading user-defined types
pg_dump: reading user-defined functions
pg_dump: reading user-defined aggregate functions
pg_dump: reading user-defined operators
pg_dump: reading user-defined operator classes
pg_dump: reading user-defined tables
pg_dump: reading table inheritance information
pg_dump: finding inheritance relationships
pg_dump: reading column info for interesting tables
pg_dump: finding the columns and types of table ...
...
pg_dump: flagging inherited columns in subtables
pg_dump: dumping out database comment
pg_dump: dumping out user-defined schemas
pg_dump: dumping out user-defined types
pg_dump: dumping out tables
pg_dump: dumping out indexes
pg_dump: dumping out user-defined procedural languages
pg_dump: dumping out user-defined functions
pg_dump: dumping out user-defined aggregate functions
pg_dump: dumping out user-defined operators
pg_dump: dumping out user-defined operator classes
pg_dump: dumping out user-defined casts
pg_dump: preparing to dump the contents of table ...
...
pg_dump: dumping foreign key constraints for table ...
...
pg_dump: dumping triggers for table ...
...
pg_dump: dumping out rules
pg_dump: dumping contents of table ...
...
pg_dump: dumping contents of table users
pg_dump: ERROR: out of memory
DETAIL: Failed on request of size 536870920.
pg_dump: SQL command to dump the contents of table "users" failed:
PQendcopy() failed.
pg_dump: Error message from server: ERROR: out of memory
DETAIL: Failed on request of size 536870920.
pg_dump: The command was: COPY public.users (<fields>) TO stdout;
pg_dump: *** aborted because of error
$

Configuration of server is :
1GB RAM

$ ipc_check

shared memory enabled: 262144 kB available

==========================

semaphores enabled
$ uname -r
4.10-RELEASE-p2
$ pg_config --version
PostgreSQL 7.4.5
$ pg_config --configure
'--with-libraries=/usr/local/lib' '--with-includes=/usr/local/include'
'--enable-nls' '--with-openssl=/usr/local' '--prefix=/usr/local'
'i386-portbld-freebsd4.10' 'LDFLAGS= -rpath=/usr/local/lib
-L/usr/local/lib -lgnugetopt' 'CFLAGS=-O2 -pipe -march=pentiumpro -O3
-funroll-loops' 'CPPFLAGS=-O2 -pipe -fmemoize-lookups -fsave-memoized
-I/usr/local/include' 'host_alias=i386-portbld-freebsd4.10'
'build_alias=i386-portbld-freebsd4.10'
'target_alias=i386-portbld-freebsd4.10' 'CC=cc'
$

I've REINDEX and VACUUM table, but it doesn't help.
Can anybody help with this ?

And a question : is the size, that pg_dump has reported (Failed on
request of size 536870920) is required size of available shared memory ?
If it is, then what ?! I need to have 10GB shared memory to dump table
whith 100'000'000 records ?!

--
With best regards,
Krok