SIGSEGV on querying using multiple connections

[dhe128]

What happens?

Concurrently querying select 1 for 8 DuckDBPyConnections, one in each thread, segfaults.

To Reproduce

Minimal reproduction:

import concurrent.futures
import faulthandler
import duckdb

faulthandler.enable()

conns = [duckdb.connect() for _ in range(8)]

def run(i):
    conns[i % 8].execute('SELECT 1').fetchall()

with concurrent.futures.ThreadPoolExecutor(8) as ex:
    for f in [ex.submit(run, i) for i in range(200)]:
        try: f.result()
        except Exception as e: print(f'{type(e).__name__}: {e}')

Expected output:
Empty, exit code 0

Actual output

RuntimeError: Could not allocate tuple object!
Fatal Python error: Segmentation fault

System: mac arm64, python3.12, duckdb 1.5.2
Also reproducible on a railway env with python 3.13, linux x86-64, duckdb 1.5.2

OS:

aarch64

DuckDB Version:

1.5.2

DuckDB Client:

1.5.2

Hardware:

No response

Full Name:

David He

Affiliation:

Intercept

Did you include all relevant configuration (e.g., CPU architecture, Linux distribution) to reproduce the issue?

• Yes, I have

Did you include all code required to reproduce the issue?

• Yes, I have

Did you include all relevant data sets for reproducing the issue?

Not applicable - the reproduction does not require a data set

[evertlammerts]

Hey @dhe128, thanks for the report. The segfault should definitely not happen, I put up #462 for that.

However, it's not possible to re-use connections across threads. You can create cursors from a connection and use those:

import concurrent.futures
import faulthandler
import duckdb

faulthandler.enable()

conns = [duckdb.connect() for _ in range(8)]

def run(i):
    conns[i % 8].cursor().execute('SELECT 1').fetchall()

with concurrent.futures.ThreadPoolExecutor(8) as ex:
    for f in [ex.submit(run, i) for i in range(200)]:
        try: f.result()
        except Exception as e: print(f'{type(e).__name__}: {e}')

This would work with a single connection as well, btw:

import concurrent.futures
import faulthandler
import duckdb

faulthandler.enable()

conn = duckdb.connect()

def run(i):
    conn.cursor().execute('SELECT 1').fetchall()

with concurrent.futures.ThreadPoolExecutor(8) as ex:
    for f in [ex.submit(run, i) for i in range(200)]:
        try: f.result()
        except Exception as e: print(f'{type(e).__name__}: {e}')