Re: pg_verify_checksums failure with hash indexes

On Wed, 29 Aug 2018 14:39:10 +0530
Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:

> On Tue, Aug 28, 2018 at 2:51 PM Peter Eisentraut
> <peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:
> >
> > This is reproducible with PG11 and PG12:
> >
> > initdb -k data
> > postgres -D data
> >
> > make installcheck
> > # shut down postgres with Ctrl-C
> >
> ..
> >
> > The files in question correspond to
> >
> > hash_i4_index
> > hash_name_index
> > hash_txt_index
> >
>
> I have looked into this problem and found the cause of it. This
> problem is happening for the empty page in the hash index. On a
> split, we allocate a new splitpoint's worth of bucket pages wherein we
> initialize the last page with zero's, this is all fine, but we forgot
> to set the checksum for that last page. Attached patch fixes the
> problem for me.
>
> Can someone try and share their findings?

I confirmed that this patch fixed the problem by setting a checksum in the last
page in hash indexes, and pg_veviry_checksum is done successfully.

regression=# select * from page_header(get_raw_page('hash_i4_index',65));
lsn | checksum | flags | lower | upper | special | pagesize | version | prune_xid
-----------+----------+-------+-------+-------+---------+----------+---------+-----------
0/41CACF0 | 18720 | 0 | 24 | 8176 | 8176 | 8192 | 4 | 0
(1 row)

By the way, I think we can fix this also by clearing the header information of the last
page instead of setting a checksum to the unused page although I am not sure which way
is better.

Regards,

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>