Thread

1. Backend crashes on select ... union

   Michael Bussmann <bus@fgan.de> — 1998-03-07T16:01:19Z

   Hi there!
   
   I played around with subselects and union and noticed that issuing strange
   statements can make the backend crash.  The problem is that other clients
   connected to the same db get disconnected as well.
   
   I issued the following statement by mistake. (x1 is a table consisting only
   of one int4 value):
   select * from x1 union select * from pg_user;
   
   This crashes the backend. Postmaster (-d 2) says:
   > NOTICE:  Message from PostgreSQL backend:
   >         The Postmaster has informed me that some other backend died
   >         abnormally and possibly corrupted shared memory.
   >         I have rolled back the current transaction and am going to
   >         terminate your database system connection and exit.
   >         Please reconnect to the database system and repeat your query.
   
   Having nothing to lose, I typed:
   create table x1 (a text, b int4);
   create table x2 (c int4, d int4);
   insert into x1 values ('Test', '123');
   insert into x2 values (1,2);
   select * from x1 union select * from x2;
   FATAL:  unrecognized data from the backend.  It probably dumped core.
   FATAL:  unrecognized data from the backend.  It probably dumped core.
   
   postmaster prints:
   >   Too Large Allocation Request("!(0 < (size) && (size) <=
   >   (0xfffffff)):size=-2 [0xfffffffe]", File: "mcxt.c", Line: 232)
   >         ProcessQuery() at Sat Mar  7 16:45:48 1998
   > 
   >   !(0 < (size) && (size) <= (0xfffffff)) (0)
   > NOTICE: Message from ... [same as above]
   
   Is there anything one can do to stop postgres from breaking all connections
   except telling your users not to type such useless statements?
   
   TIA
   
   MfG
   MB
   
   PS: I noticed that NO_ASSERT_CHECKING is undef'ed by default (so assert
   checking is enabled) and will only be defined if you specify either 
   --enable-cassert or --disable-cassert.
   The INSTALL file, however, says assert checking is disabled by default (so
   NO_ASSERT_CHECKING should be set). Am I confusing something, or is it
   configure that gets confused?
   
   -- 
   Michael Bussmann <bus@fgan.de> [Tel.: +49 228 9435 211; Fax: +49 228 348953]
   Today's Excuse:
           static from plastic slide rules
   
   

2. Re: [HACKERS] Backend crashes on select ... union

   Bruce Momjian <maillist@candle.pha.pa.us> — 1998-03-07T21:16:29Z

   > 
   > Hi there!
   > 
   > I played around with subselects and union and noticed that issuing strange
   > statements can make the backend crash.  The problem is that other clients
   > connected to the same db get disconnected as well.
   > 
   > I issued the following statement by mistake. (x1 is a table consisting only
   > of one int4 value):
   > select * from x1 union select * from pg_user;
   > 
   
   My fault.  I never went back to make sure all union columns have the same
   types.  I will work on that.
   
   -- 
   Bruce Momjian                          |  830 Blythe Avenue
   maillist@candle.pha.pa.us              |  Drexel Hill, Pennsylvania 19026
     +  If your life is a hard drive,     |  (610) 353-9879(w)
     +  Christ can be your backup.        |  (610) 853-3000(h)