Почему postgresql выдает ошибку «возможно, не хватает места на диске», когда на диске достаточно места?

Я запускаю этот запрос в postgresql на Ubuntu 12.0.4:

SELECT t2.p AS prop, t2.o AS obj, COUNT(t2.o) AS num 
FROM "class_Event" AS t1, 
  ((SELECT s,p,o FROM "prop_sliceHasAnomaly")  
   UNION (SELECT s,p,o FROM "prop_eventHasDuration")  
   UNION (SELECT s,p,o FROM "prop_sliceHasEndEvent")  
   UNION (SELECT s,p,o FROM "prop_eventPrecedeInCPU")  
   UNION (SELECT s,p,o FROM "prop_eventFollowInTask")  
   UNION (SELECT s,p,o FROM "prop_topObjectProperty")  
   UNION (SELECT s,p,o FROM "prop_eventDetails")  
   UNION (SELECT s,p,o FROM "prop_switchTo")  
   UNION (SELECT s,p,o FROM "prop_eventIsExecutedOn")  
   UNION (SELECT s,p,o FROM "prop_runningAction")  
   UNION (SELECT s,p,o FROM "prop_anomalyHasSlice")  
   UNION (SELECT s,p,o FROM "prop_eventPrecedeInTrace")  
   UNION (SELECT s,p,o FROM "prop_sliceHasStartEvent")  
   UNION (SELECT s,p,o FROM "prop_eventHasActiveDuration")  
   UNION (SELECT s,p,o FROM "prop_eventFollowInTrace")  
   UNION (SELECT s,p,o FROM "prop_runningTask")  
   UNION (SELECT s,p,o FROM "prop_eventOrdering")  
   UNION (SELECT s,p,o FROM "prop_domain")  
   UNION (SELECT s,p,o FROM "prop_sliceHasFunctionality")  
   UNION (SELECT s,p,o FROM "prop_traceContainsEvent")  
   UNION (SELECT s,p,o FROM "prop_eventHasDurationFromPreviousOccurrence")  
   UNION (SELECT s,p,o FROM "prop_eventPrecedeOccurrence")  
   UNION (SELECT s,p,o FROM "prop_eventPrecedeinTask")  
   UNION (SELECT s,p,o FROM "prop_switchFrom")  
   UNION (SELECT s,p,o FROM "prop_eventEndAt")  
   UNION (SELECT s,p,o FROM "prop_subPropertyOf")  
   UNION (SELECT s,p,o FROM "prop_eventFollowOccurrence")  
   UNION (SELECT s,p,o FROM "prop_eventFollowInCPU")  
   UNION (SELECT s,p,o FROM "prop_subClassOf")  
   UNION (SELECT s,p,o FROM "prop_eventHasDurationToNextOccurrence")  
   UNION (SELECT s,p,o FROM "prop_requestComponent")  
   UNION (SELECT s,p,o FROM "prop_eventStartAt")  
   UNION (SELECT s,p,o FROM "prop_range")  
   UNION (SELECT s,p,o FROM "prop_functionalityHasSlice") ) AS t2 
WHERE t1.s = t2.s 
GROUP BY t2.p, t2.o 
HAVING (COUNT(t2.o) > 1) 

Но я вышел с этой ошибкой из posgresql:

ERROR:  could not write block 713 of temporary file: Aucun espace disponible sur le périphérique
HINT:  Perhaps out of disk space?

********** Erreur **********

ERROR: could not write block 713 of temporary file: Aucun espace disponible sur le périphérique
État SQL :53100
Astuce : Perhaps out of disk space?

Я проверил достаточно ли места на диске с помощью команды df -h

df -h
df: «/var/lib/lightdm/.gvfs»: Permission non accordée
Sys. de fichiers Taille Utilisé Dispo Uti% Monté sur
/dev/sda5           37G     35G   46M 100% /
udev                16G    4,0K   16G   1% /dev
tmpfs              6,3G    984K  6,3G   1% /run
none               5,0M       0  5,0M   0% /run/lock
none                16G    216K   16G   1% /run/shm
/dev/sda6           37G    411M   35G   2% /opt
/dev/sda9          499G    435G   40G  92% /home
/dev/sda7           37G    4,7G   30G  14% /usr
/dev/sda8           37G    5,1G   30G  15% /usr/local

и кажется, что на диске /home есть свободное место 40GB. Вот мне и интересно, что заставляет эту ошибку поднимать? есть ли параметр ограничения дискового пространства, который можно установить в конфигурации postgresql?

у кого-то есть идея по этому поводу?