One of our clients caught an error "failed to find parent tuple for
heap-only tuple at (50661,130) in table "tbl'" in PostgreSQL v12.
Steps to reproduce (REL_12_STABLE):
1) Create table with primary key, create brin index, fill table with
some initial data:
create table tbl (id int primary key, a int) with (fillfactor=50);
create index idx on tbl using brin (a) with (autosummarize=on);
insert into tbl select i, i from generate_series(0,100000) as i;
2) Run script test_brin.sql using pgbench:
pgbench postgres -f ../review/brin_test.sql -n -T 120
The script is a bit messy because I was trying to reproduce a
problematic workload. Though I didn't manage to simplify it.
The idea is that it inserts new values into the table to produce
unindexed pages and also updates some values to trigger HOT-updates on
these pages.
3) Open psql session and run brin_summarize_new_values
select brin_summarize_new_values('idx'::regclass::oid); \watch 2
Wait a bit. And in psql you will see the ERROR.
This error is caused by the problem with root_offsets array bounds. It
occurs if a new HOT tuple was inserted after we've collected
root_offsets, and thus we don't have root_offset for tuple's offnum.
Concurrent insertions are possible, because brin_summarize_new_values()
only holds ShareUpdateLock on table and no lock (only pin) on the page.
The draft fix is in the attachments. It saves root_offsets_size and
checks that we only access valid fields.
Patch also adds some debug messages, just to ensure that problem was caught.
TODO:
- check if heapam_index_validate_scan() has the same problem
- code cleanup
- test other PostgreSQL versions
[1]
https://www.postgresql.org/message-id/flat/CA%2BTgmoYgwjmmjK24Qxb_vWAu8_Hh7gfVFcr3%2BR7ocdLvYOWJXg%40mail.gmail.com
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Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company