Re: BUG #18314: PARALLEL UNSAFE function does not prevent parallel index build
| От | Tender Wang |
|---|---|
| Тема | Re: BUG #18314: PARALLEL UNSAFE function does not prevent parallel index build |
| Дата | |
| Msg-id | CAHewXNkPK9F-0fQ8komhJ_fW6Sk=QL4YDvTjVZwqBM2ZEzTd+A@mail.gmail.com обсуждение исходный текст |
| Ответ на | BUG #18314: PARALLEL UNSAFE function does not prevent parallel index build (PG Bug reporting form <noreply@postgresql.org>) |
| Ответы |
Re: BUG #18314: PARALLEL UNSAFE function does not prevent parallel index build
|
| Список | pgsql-bugs |
Thanks for reporting this issue.
I debug the process of creating index, and in plan_create_index_workers() func, which use the planner to
decide if use parallel building index.
But the index expression passed to is_parallel_safe() has already simplified by RelationGetIndexExpressions() func.
In this case, FunExpr node will be simplified to Const node. So the check in is_parallel_safe() will return true.
The goal of plan_create_index_workers() is to decide whether it's safe to build index parallelly. I think we just check the raw index
expression no need to simplify the index expression.
PG Bug reporting form <noreply@postgresql.org> 于2024年1月29日周一 19:02写道：
The following bug has been logged on the website:
Bug reference: 18314
Logged by: Alexander Lakhin
Email address: exclusion@gmail.com
PostgreSQL version: 16.1
Operating system: Ubuntu 22.04
Description:
When planner chooses to perform parallel index build, it doesn't
check whether functions used in an index expression or predicate are
parallel-safe. For example:
CREATE FUNCTION f() RETURNS int IMMUTABLE PARALLEL UNSAFE
AS $$
BEGIN
RETURN 0;
EXCEPTION WHEN OTHERS THEN
RETURN 1;
END$$ LANGUAGE plpgsql;
CREATE TABLE t(i int);
INSERT INTO t SELECT g FROM generate_series(1, 300000) g;
CREATE INDEX ON t((i + f()));
results in:
ERROR: cannot start subtransactions during a parallel operation
CONTEXT: PL/pgSQL function f() line 2 during statement block entry
parallel worker
Although with 200000 records, the index created with no error.
Reproduced on REL_12_STABLE .. master.
Tender Wang
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