When i use the system to do some queries,for example:select *,oid from testtable,i do it several times and then 
error will appear:
   Server closed the connection unexpectedly
           This probably means the server terminated abnormally before or while processing the request
    The connection to the server was lost.Attempting reset:DEBUG:server process(pid 1654)was terminated by signal 11
    DEBUG:......
 and then i am kicked from the database.I have to do "psql testdb" another time,but i do the query some times,the error
appear again.
   Why does this happen?