Re: Segmentation fault - PostgreSQL 17.0

On 11/11/24 16:20, Ľuboslav Špilák wrote:
> Hello.
> 
> I had similar ly created table in a different schema, so there were
> truly 2 rows in the given select (but the 2^nd  one was created to test
> the problem), so even after  removing one of them the problem still
> persists.
> 
> *select* * *from* pg_class *where* relname='test_idxbrin';
>
"oid","relname","relnamespace","reltype","reloftype","relowner","relam","relfilenode","reltablespace","relpages","reltuples","relallvisible","reltoastrelid","relhasindex","relisshared","relpersistence","relkind","relnatts","relchecks","relhasrules","relhastriggers","relhassubclass","relrowsecurity","relforcerowsecurity","relispopulated","relreplident","relispartition","relrewrite","relfrozenxid","relminmxid","relacl","reloptions","relpartbound"
>
1128187015,test_idxbrin,2200,0,0,10,3580,1128187015,0,3,0.0,0,0,false,false,p,i,1,0,false,false,false,false,false,true,n,false,0,"0","0",,{pages_per_range=32},
>
1128178819,test_idxbrin,16830,0,0,10,3580,1128178819,0,3,0.0,0,0,false,false,p,i,1,0,false,false,false,false,false,true,n,false,0,"0","0",,{pages_per_range=32},
> 
> So we removed one of the tables with this index and now this select
> returned one row
> 
>  *select* * *from* pg_class *where* relname='test_idxbrin';
>
"oid","relname","relnamespace","reltype","reloftype","relowner","relam","relfilenode","reltablespace","relpages","reltuples","relallvisible","reltoastrelid","relhasindex","relisshared","relpersistence","relkind","relnatts","relchecks","relhasrules","relhastriggers","relhassubclass","relrowsecurity","relforcerowsecurity","relispopulated","relreplident","relispartition","relrewrite","relfrozenxid","relminmxid","relacl","reloptions","relpartbound"
>
1128178819,test_idxbrin,16830,0,0,10,3580,1128178819,0,3,0.0,0,0,false,false,p,i,1,0,false,false,false,false,false,true,n,false,0,"0","0",,{pages_per_range=32},
> 
> 
> Then we called the problematic function again and it crashed.
> 

Ah, I see. I've been looking at this assuming the descriptor is for the
index, when in fact it's for the result, which actually has more
attributes (so my comment about the index having just 1 attribute was
misguided).

But now I noticed an interesting thing - if I print the descriptor in
heap_compute_data_size, I get this:

(gdb) p *tupleDesc
$1 = {natts = 8, tdtypeid = 2249, tdtypmod = 0, tdrefcount = -1, constr
= 0x0, attrs = 0xb2d29b0}

There's 8 attributes, not 7 (which is what you get).

Well, the reason is likely pretty simple - I'd bet you have pageinspect
at version 1.11 (or older), which didn't know about empty ranges. And
1.12 added that, and the C code dutifully fills that. But the descriptor
is derived from the function signature, and that doesn't have that
attribute. So it tries to interpret 0 (=false) as a pointer, and that
just segfaults.

If you do \dx (or select * from pg_extension), what version you get for
pageinspect? And if you do "\df brin_page_items" does it have "empty" as
one of the output arguments?

You can try "alter extension pageinspect update" to update the function
signatures, etc. That should make the segfault go away.

I can reproduce this by installing pageinspect 1.11 and running the
brin_page_items() query. What a stupid bug, I should have thought about
this when adding the "empty" field.

Thanks for the report!


regards

-- 
Tomas Vondra