SQLite3 multithreading cache inconsistency
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Descrição
Bug report
Bug description:
When using SQLite3 in multi-threading application, the fetch reuslts are not consistent. After some testing, this seems to be caused by the caching.
The SQLite threading mode is serialized.
This issue only exists in python 3.12 and 3.13. No issue in 3.11.
Currently solution is to set cached_statements=0 when connect to the database.
A simple demo to reproduce the error:
import sqlite3
import threading
KB = sqlite3.connect(
"example.db", check_same_thread=False
)
def execute_query():
cursor = KB.cursor()
cursor.execute("SELECT * FROM test_table")
result = cursor.fetchall()
assert result == [(1, 'test1'), (2, 'test2'), (3, 'test3')], str(result)
return result
def run_threads():
threads = []
for i in range(50):
thread = threading.Thread(target=execute_query)
threads.append(thread)
thread.start()
for thread in threads:
thread.join()
def test_multithreading():
cursor = KB.cursor()
cursor.execute(
"""CREATE TABLE IF NOT EXISTS test_table (id INTEGER PRIMARY KEY, value TEXT)"""
)
KB.commit()
cursor.execute("""DELETE FROM test_table""")
KB.commit()
cursor.execute("""INSERT INTO test_table (value) VALUES ('test1')""")
cursor.execute("""INSERT INTO test_table (value) VALUES ('test2')""")
cursor.execute("""INSERT INTO test_table (value) VALUES ('test3')""")
KB.commit()
run_threads()
KB.close()
if __name__ == "__main__":
test_multithreading()
Test output: (Different in each run because of inconsistent fetch results)
Exception in thread Thread-3 (execute_query):
Traceback (most recent call last):
File "/usr/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
self.run()
File "/usr/lib/python3.12/threading.py", line 1010, in run
Exception in thread Thread-7 (execute_query):
Traceback (most recent call last):
File "/usr/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
self._target(*self._args, **self._kwargs)
File "/home/user/tmp/kb_test.py", line 13, in execute_query
self.run()
File "/usr/lib/python3.12/threading.py", line 1010, in run
Exception in thread Thread-12 (execute_query):
Traceback (most recent call last):
File "/usr/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
assert result == [(1, 'test1'), (2, 'test2'), (3, 'test3')], str(result)
self._target(*self._args, **self._kwargs)
AssertionError: [(1, 'test2'), (3, 'test3')]
File "/home/user/tmp/kb_test.py", line 13, in execute_query
Exception in thread Thread-1 (execute_query):
Traceback (most recent call last):
File "/usr/lib/python3.12/threading.py", line 1073, in _bootstrap_inner
self.run()
assert result == [(1, 'test1'), (2, 'test2'), (3, 'test3')], str(result)
self.run()
AssertionError: [(3, 'test3')]
File "/usr/lib/python3.12/threading.py", line 1010, in run
File "/usr/lib/python3.12/threading.py", line 1010, in run
self._target(*self._args, **self._kwargs)
File "/home/user/tmp/kb_test.py", line 13, in execute_query
self._target(*self._args, **self._kwargs)
File "/home/user/tmp/kb_test.py", line 13, in execute_query
assert result == [(1, 'test1'), (2, 'test2'), (3, 'test3')], str(result)
assert result == [(1, 'test1'), (2, 'test2'), (3, 'test3')], str(result)
AssertionError: [(None, None), (), (2, 'test2'), (), (), (2, 'test2'), (0, None), (1, 'test1'), (2, 'test2'), (3, 'test3')]
AssertionError: [(3, 'test3')]
CPython versions tested on:
3.12, 3.13
Operating systems tested on:
Linux
Guia de contribuição
Primeiros passos
- Leia a issue inteira e depois o guia de contribuição do projeto.
- Comente na issue dizendo que vai assumir — evita que duas pessoas façam o mesmo trabalho.
- Faça um fork do repositório e trabalhe em uma branch.
- Abra um pull request que referencie o número da issue.
Direção de pesquisa
Comece com o reprodutor Python fornecido para sqlite3.connect(), comparando Python 3.11 com 3.12 e 3.13 enquanto executa a consulta com 50 threads e varia cached_statements. Investigue o comportamento do cache de statements do sqlite3 no modo de threading serializado do SQLite. Considera-se concluído quando a busca com threads retorna consistentemente as três linhas esperadas sem exigir cached_statements=0.
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Avaliação
- Stack de tecnologia
- python, sqlite
- Domínio
- databases
- Tipo de issue
- Bug
- Dificuldade
- 4/5
- Tempo estimado
- 3-5 dias
- Status de atividade
- Estagnada
- Clareza
- Precisa de esclarecimento
- Facilidade para iniciantes
- 35/100