Re: pgsql: Skip full index scan during cleanup of B-tree indexes when possi

On Thu, Apr 5, 2018 at 2:26 PM, Alexander Korotkov <
a(dot)korotkov(at)postgrespro(dot)ru> wrote:

> On Thu, Apr 5, 2018 at 6:28 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Peter Geoghegan <pg(at)bowt(dot)ie> writes:
>> >>> TRAP: FailedAssertion("!(metad->btm_version == 3)", File:
>> >>> "/home/pg/postgresql/root/build/../source/src/backend/access
>> /nbtree/nbtpage.c",
>> >>> Line: 619)
>>
>> >> Hm, buildfarm's not complaining --- what's the test case?
>>
>> > This was discovered while testing/reviewing the latest version of the
>> > INCLUDE covering indexes patch. It now seems to be unrelated.
>>
>> Oh, wait ... I wonder if you saw that because you were running a new
>> backend without having re-initdb'd? Once you had re-initdb'd, then
>> of course there would be no old-format btree indexes anywhere. But
>> if you hadn't, then anyplace that was not prepared to cope with the
>> old header format would complain about pre-existing indexes.
>>
>> In short, this sounds like a place that did not get the memo about
>> how to cope with un-upgraded indexes.
>>
>
> That's an issue, because meta-page should be upgraded "on the fly".
> That was tested, but perhaps without assertions. I'll investigate more on
> this an propose a fix.
>

So, "Assert(metad->btm_version == BTREE_VERSION)" was failed, because
metadata was copied from meta page to rel->rd_amcache "as is" with
metad->btm_version == BTREE_MIN_VERSION.

Without assert everything works fine, because extended metadata fields are
never used from rel->rd_amcache. So my first intention was to relax this
assert to Assert(metad->btm_version >= BTREE_MIN_VERSION && metad->btm_version
<= BTREE_VERSION).
But then I still have concern that we copy metadata beyond pd_lower
when metapage is in old format.

memcpy(rel->rd_amcache, metad, sizeof(BTMetaPageData));

This is why I decided to write separate function to handle caching of
metadata,
which takes care about filling unavailable fields of metadata with default
values.
I also made same fix for pageinspect. Patch is attached.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company