On Sunday, February 9, 2014 1:00:58 PM UTC+2, Chris Angelico wrote:
> The biggest downside of SQLite3 is concurrency. I haven't dug into the
> exact details of the pager system and such, but it seems to be fairly
> coarse in its locking. Also, stuff gets a bit complicated when you do
> a single transaction involving multiple files. So if you have lots of
> processes writing to the same set of SQLite tables, you'll see pretty
> poor performance.
> ChrisA
Hi Chris
i simply tested running 2 independent processes started at same time in
parallel towards same sqlite database and never get 20000 in that row
though used exclusive lock on DB. might be i did something wrong.
p.s. threading locks don't do anything in this example.
import sqlite3
import threading
#from threading import Lock
# Constants
CNT_DB_NAME = "messageid.db"
class MessageId:
'''
--------------------------------------------------------------------------
Following must be done in advance:
- Create DB sqlite3 sqlite_msgd.db
- Create table CREATE TABLE msgid (id INTEGER PRIMARY KEY, val
INTEGER);
- Inser def INSERT INTO msgid VALUES (0, 0);
--------------------------------------------------------------------------'''
def __init__(self, dflag = False, dbname = 'messageid.db'):
#print(type(self))
#print(id(self))
self._debug = dflag
self._lock = threading.Lock()
self._dbname = dbname
if self._debug:
print("MessageId.__init__(dbname = {0})".format(dbname))
def get_msgid(self):
'''
--------------------------------------------------------------------------
- Acquire lock
- Connect to database
- Select current value SELECT val FROM msgid WHERE id = 0;
- Increment current value
- Insert a row of data UPDATE msgid SET val = 1 WHERE id =
new_val;
--------------------------------------------------------------------------'''
self._lock.acquire(True, 1)
conn = sqlite3.connect('example.db', 10.0, True, "EXCLUSIVE")
c = conn.cursor()
c.execute("SELECT val FROM msgid WHERE id = 0")
tint = int(c.fetchone()[0]) + 1
c.execute("UPDATE msgid SET val={0} WHERE id = 0".format(tint))
conn.commit()
conn.close()
self._lock.release()
if self._debug:
print("MessageId.get_msgid() = ", tint)
return tint
tclass = MessageId()
for k in range(10000):
tclass.get_msgid()
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