Thread: [HACKERS] wrong t_bits alignment in pageinspect

Hi!


I found out the problem in exposing values of t_bits field from 
heap_page_items function.

When the number of attributes in table is multiple of eight, t_bits 
column shows double number of bits in which data fields are included.

For example:

# create table tbl(f1 int, f2 int, f3 int, f4 int, f5 int, f6 int, f7 
int, f8 int);
# insert into tbl(f1, f8) values (x'f1'::int, 0);

# select t_bits, t_data from heap_page_items(get_raw_page('tbl', 0));

                    t_bits      |       t_data
            ------------------+--------------------
  1000000110001111 | \xf100000000000000

I suppose the prefix 10000001 corresponds to real value of t_bits, the 
rest part 10001111 - to the lower byte of f1 field of tbl.


Attached patch fixes this issue.


-- 
Regards,
Maksim Milyutin

Hi!
> 15 дек. 2017 г., в 18:53, Maksim Milyutin <milyutinma@gmail.com> написал(а):
>
> I found out the problem in exposing values of t_bits field from heap_page_items function.

Probably, this [0] place contains similar bug too?
Also, may be macro HeapTupleHeaderGetNatts() will be a little bit easier to read.

Best regards, Andrey Borodin.

[0] https://github.com/postgres/postgres/blob/master/contrib/pageinspect/heapfuncs.c#L439

Hi!


02.01.2018 12:33, Andrey Borodin wrote:
>> 15 дек. 2017 г., в 18:53, Maksim Milyutin <milyutinma@gmail.com> написал(а):
>>
>> I found out the problem in exposing values of t_bits field from heap_page_items function.
> Probably, this [0] place contains similar bug too?
>
> [0] https://github.com/postgres/postgres/blob/master/contrib/pageinspect/heapfuncs.c#L439

Yes, it's so. Thanks a lot for notice.

Attached a new version of patch with regression test.

-- 
Regards,
Maksim Milyutin

The following review has been posted through the commitfest application:
make installcheck-world:  tested, passed
Implements feature:       not tested
Spec compliant:           tested, passed
Documentation:            tested, passed

Everything is fixed, works properly and I have no new notices.
I think that patch is ready for committer.

Best regards, Andrey Borodin.

The new status of this patch is: Ready for Committer

Maksim Milyutin <milyutinma@gmail.com> writes:
> Attached a new version of patch with regression test.

Looks good, pushed.

I also removed one error check from tuple_data_split --- there doesn't
seem to be a lot of point in checking that bits_str_len is some multiple
of 8 when we're about to check that it's equal to a particular multiple
of 8.

            regards, tom lane