Re: BUG #16925: ERROR: invalid DSA memory alloc request size 1073741824 CONTEXT: parallel worker

Hi! Thank you for your work on the subject.

On 11.12.2023 02:30, Alena Rybakina wrote:
>
> On 06.12.2023 07:46, Andrei Lepikhov wrote:
>> On 18/3/2021 16:21, Thomas Munro wrote:
>>> ===8<===
>>> shared_buffers=2GB
>>> fsync=off
>>> max_wal_size=10GB
>>> min_dynamic_shared_memory=2GB
>>> ===8<===
>>> create table bigger_than_it_looks as
>>>    select generate_series(1, 256000000) as id;
>>> alter table bigger_than_it_looks set (autovacuum_enabled = 'false');
>>> alter table bigger_than_it_looks set (parallel_workers = 1);
>>> analyze bigger_than_it_looks;
>>> update pg_class set reltuples = 5000000 where relname =
>>> 'bigger_than_it_looks';
>>> ===8<===
>>> postgres=# set work_mem = '4.5GB';
>>> SET
>>> postgres=# explain analyze select count(*) from bigger_than_it_looks
>>> t1 join bigger_than_it_looks t2 using (id);
>>> ERROR:  invalid DSA memory alloc request size 1073741824
>>> CONTEXT:  parallel worker
>>> ===8<===
>>
>> This bug still annoyingly interrupts the queries of some clients.
>> Maybe complete this work?
>> It is stable and reproduces on all PG versions. The case:
>> work_mem = '2GB'
>>
>> test table:
>> -----------
>> CREATE TABLE bigger_than_it_looks AS
>>   SELECT generate_series(1, 512E6) AS id;
>> ALTER TABLE bigger_than_it_looks SET (autovacuum_enabled = 'false');
>> ALTER TABLE bigger_than_it_looks SET (parallel_workers = 1);
>> ANALYZE bigger_than_it_looks;
>> UPDATE pg_class SET reltuples = 5000000
>> WHERE relname = 'bigger_than_it_looks';
>>
>> The parallel workers number impacts size of the allowed memory under
>> the hash table and in that sense correlates with the work_mem value,
>> needed for the bug reproduction (keep in mind also that
>> hash_mem_multiplier has been changed recently).
>>
>> Query:
>> SELECT sum(a.id)
>> FROM bigger_than_it_looks a
>> JOIN bigger_than_it_looks b ON a.id =b.id
>> LEFT JOIN bigger_than_it_looks c ON b.id = c.id;
>>
>> Any query that needs Parallel Hash Join can be found here. The case
>> here is as follows.
>> The first batch contains a lot of tuples (on increment, it has about
>> 67mln tuples.). We calculate the number of buckets needed,
>> approximately 134 mln (134217728). Remember, the size of
>> dsa_pointer_atomic is 8 in my case, and it ends up with an overflow
>> of the max number of DSA, which can be allocated (1073741823 bytes).
>> See the new patch in the attachment.
I've looked through your code and haven't seen any errors yet, but I
think we could rewrite these lines of code as follows:

-                    dbuckets = ceil(dtuples / NTUP_PER_BUCKET);
-                    dbuckets = Min(dbuckets, max_buckets);
-                    new_nbuckets = (int) dbuckets;
-                    new_nbuckets = Max(new_nbuckets, 1024);
+                    dbuckets = Min(ceil(dtuples / NTUP_PER_BUCKET),
max_buckets);
+                    new_nbuckets = Max((int) dbuckets, 1024);

I have attached a diff file with the proposed changes to this email.

--
Regards,
Alena Rybakina
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company