Re: BUG #17406: Segmentation fault on GiST index after 14.2 upgrade

On 2/23/22 16:41, Tomas Vondra wrote:
> On 2/23/22 16:36, Tomas Vondra wrote:
>>>
>>> I got approval to send a table with its data and index in the subject
>>> datafile.
>>> Taken from the v14 database.
>>>
>>
>> Thanks for the data! I've been able to reproduce the issue (load into
>> 12, pg_upgrade to 14 and run the query). After bisecting this for a
>> while, this seems like a bug in PG13 commit
>>
>> commit 911e70207703799605f5a0e8aad9f06cff067c63 (HEAD)
>> Author: Alexander Korotkov <akorotkov@postgresql.org>
>> Date:   Mon Mar 30 19:17:11 2020 +0300
>>
>>     Implement operator class parameters
>>
>>     ...
>>
>> It works fine when upgrading to an earlier build, and crashes since this
>> commit. I haven't investigated this further, but I guess there's some
>> thinko in gist_ltree_ops, affecting how we interpret existing indexes.
>>
>> Alexander, any ideas?
>>
> 
> Sorry, I accidentally used Alexander's old address, so let me CC him
> with the correct/current one.
> 

I tried investigating this a bit further, but my gist-foo is rather
limited so I haven't made much progress so far. But as Victor already
mentioned, REINDEX fixes this - so I tried comparing the broken index
with a new one built on PG13.

And the it seems the indexes are mostly the same, with the exception of
LSN in the page header. The only page that substantially differs is the
first page, which is also storing less data (the broken version):

test=# SELECT * FROM
page_header(get_raw_page('v3_region_copy_ltree_path_idx', 0));
    lsn    | checksum | flags | lower | upper | special | pagesize | ...
----------+----------+-------+-------+-------+---------+----------+- ...
 0/1CD80C8 |        0 |     0 |    40 |  7856 |    8176 |     8192 | ...
  (1 row)

test=# SELECT * FROM
page_header(get_raw_page('v3_region_copy_13_ltree_path_idx', 0));
    lsn    | checksum | flags | lower | upper | special | pagesize | ...
-----------+----------+-------+-------+-------+---------+----------+-...
 0/7029760 |        0 |     0 |    40 |  7760 |    8176 |     8192 | ...
(1 row)


regards

-- 
Tomas Vondra
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