Re: ERROR: could not read block 0 in file when creating an index out of a function

On Wed, Mar 12, 2025 at 12:54 PM Artur Zakirov <zaartur@gmail.com> wrote:

I can reproduce this with the table `t` on PG 15.10.

I didn't mention I'm running 16.6, but I'm pretty sure it is
reproducible on other versions too.

In your case `base/357283/365810` file is a new index file. For some
reason Postgres tries to read the new index. I suppose this is because
during reading the table `t` within the function `f_t` it tries to
access the new index.

Yeah, even if it is not clear to me why it is trying to read the index
that is under creation (i.e., not usable yet).

According to the documentation, IMMUTABLE functions should not only
modify the database, but also return the same results given the same
arguments forever, which might not be true when you query a table
within such a function. Such a function should be defined as STABLE or
VOLATILE.

As I stated, this example is controversial, and as the documentation
states, the IMMUTABLE set of functions should not perform database
lookups, as in my example.
However, the error message is quite obscure to me, and reminds me a
disk corruption rather a stability/function/lookup problem.

Test on 17.0:

It seems inconsistent to me :

creating a fresh ttt (no PK no constraint) :

amantzio@[local]/test=# CREATE INDEX IF NOT EXISTS idx_t ON ttt( f_ttt( pk ) );
CREATE INDEX
amantzio@[local]/test=# drop index idx_t ;
DROP INDEX
amantzio@[local]/test=# ALTER TABLE ttt ALTER pk SET NOT NULL ;
ALTER TABLE
amantzio@[local]/test=# CREATE INDEX IF NOT EXISTS idx_t ON ttt( f_ttt( pk ) );
ERROR:  could not read blocks 0..0 in file "base/17753/596558047": read only 0 of 8192 bytes
CONTEXT:  SQL statement "SELECT pk
                 FROM public.ttt
WHERE pk = i"
PL/pgSQL function f_ttt(integer) line 5 at SQL statement
amantzio@[local]/test=# ALTER TABLE ttt ALTER pk DROP NOT NULL ;
ALTER TABLE
amantzio@[local]/test=# CREATE INDEX IF NOT EXISTS idx_t ON ttt( f_ttt( pk ) );
ERROR:  could not read blocks 0..0 in file "base/17753/596558048": read only 0 of 8192 bytes
CONTEXT:  SQL statement "SELECT pk
                 FROM public.ttt
WHERE pk = i"
PL/pgSQL function f_ttt(integer) line 5 at SQL statement
amantzio@[local]/test=#  
\q

So yep you are definitely right as far as the error message is concerned plus the inconsistent pattern shown above.

Luca