Re: pg11.1 jit segv - Mailing list pgsql-hackers

On Thu, Nov 15, 2018 at 04:17:51PM -0800, Andres Freund wrote:
> I'm about to commit some changes to 12/master that'd possibly make it
> easier to find issues like this.

Are you referring to this  a future commit ?
commit 763f2edd92095b1ca2f4476da073a28505c13820
Rejigger materializing and fetching a HeapTuple from a slot.

I was able to reproduce under HEAD with pg_restored data.

I guess you're right that the "memory alloc failure" is related/same thing,
I've seen it intermittently with queries which also sometimes crash (and also
sometimes don't).

Note that when it crashes, it seems to take a longer time to do so than the
query would normally take.  Like we're walking off the end of an array, say.

I've been able to reproduce the crash with a self join of a table (no view, no
expressions, no parallel, directly querying a relkind='r' child).  In that
case, enable_bitmapscan=on and jit_tuple_deforming=on are both needed to crash,
and jit_debugging_support=on does not yield a useful bt.

The table is not too special, but was probably ALTERed to add columns a good
number of times by one of our processes.  It has ~1100 columns, including
arrays, and some with null_frac=1.  I'm trying to come up with a test case
involving column types and order.

(gdb) bt
#0  0x00007f81a08b8b98 in ?? ()
#1  0x0000000000000000 in ?? ()

ts=# SET jit=on;SET jit_above_cost=0;explain(analyze off,verbose off) SELECT a.* FROM
child.daily_eric_umts_rnc_utrancell_view_201804a JOIN child.daily_eric_umts_rnc_utrancell_view_201804 b
USING(start_time,sect_id)WHERE a.start_time BETWEEN '2018-04-30' AND '2018-05-04' AND b.start_time BETWEEN '2018-04-30'
AND'2018-05-04';
 
SET
SET
                                                                                 QUERY PLAN
                                                    
 

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Hash Join  (cost=527.36..1038.17 rows=1 width=7760)
   Hash Cond: ((a.start_time = b.start_time) AND (a.sect_id = b.sect_id))
   ->  Bitmap Heap Scan on daily_eric_umts_rnc_utrancell_view_201804 a  (cost=9.78..515.59 rows=133 width=7760)
         Recheck Cond: ((start_time >= '2018-04-30 00:00:00'::timestamp without time zone) AND (start_time <=
'2018-05-0400:00:00'::timestamp without time zone))
 
         ->  Bitmap Index Scan on daily_eric_umts_rnc_utrancell_view_201804_unique_idx  (cost=0.00..9.74 rows=133
width=0)
               Index Cond: ((start_time >= '2018-04-30 00:00:00'::timestamp without time zone) AND (start_time <=
'2018-05-0400:00:00'::timestamp without time zone))
 
   ->  Hash  (cost=515.59..515.59 rows=133 width=12)
         ->  Bitmap Heap Scan on daily_eric_umts_rnc_utrancell_view_201804 b  (cost=9.78..515.59 rows=133 width=12)
               Recheck Cond: ((start_time >= '2018-04-30 00:00:00'::timestamp without time zone) AND (start_time <=
'2018-05-0400:00:00'::timestamp without time zone))
 
               ->  Bitmap Index Scan on daily_eric_umts_rnc_utrancell_view_201804_unique_idx  (cost=0.00..9.74 rows=133
width=0)
                     Index Cond: ((start_time >= '2018-04-30 00:00:00'::timestamp without time zone) AND (start_time <=
'2018-05-0400:00:00'::timestamp without time zone))
 
 JIT:
   Functions: 19
   Options: Inlining false, Optimization false, Expressions true, Deforming true

BTW find attached patch which I believe corrects some comments.

Justin