Michael Bayer wrote:
>
> On Jan 9, 2007, at 5:24 AM, Michele Petrazzo wrote:
>> Because, like what I wrote on the psycopg2 ml (lists.initd.org/
>> pipermail/psycopg/2007-January/005250.html)
>> without the "server side cursor", the memory usage on the client
>> side is proportionally at the number of records returned by the
>> query (on my example 400k records, 60MB ram). I think because the
>> driver fetch all the data from the server and leave it available
>> with the fetchXXX methods.
>
> really ? im not sure about psycopg2 specifically,
Here, sure! Assuming the I'm on linux and I have "ps" utility locally.
The db are on the same machine where I'm making tests. PG are 8.1.5 and
psycopg2 2.0.4.
This is my test:
<-code->
import time
import subprocess as SP
import psycopg2
NAMED_CURSOR = 1
def get_mem():
#Wait for the memory stabilization
time.sleep(0.5)
#get the memory usage with ps.
output = SP.Popen(["ps","-eo","rss,args"],
stdout=SP.PIPE).communicate()[0]
for line in output.split('\n'):
if not line: continue
mem, pr_name = line.split(None,1)
#show only the my python exe
if not "python " + __file__ in pr_name: continue
return mem
def create_cur():
if NAMED_CURSOR:
return con.cursor("test")
else:
return con.cursor()
def exec_q(q):
cur = create_cur()
print "empty cursor ", get_mem()
cur.execute(q)
print "cursor after execute ", get_mem()
print "result --", cur.fetchone()
print "after fetchone ", get_mem()
cur.close()
print "cursor closed ", get_mem()
print "python and modules ", get_mem()
con = psycopg2.connect('user=test password=test dbname=book')
print "connection ", get_mem()
exec_q("SELECT COUNT(id) FROM book")
exec_q("SELECT * FROM book")
</-code->
## with NAMED_CURSOR = 1
michele:~/tmp$ time python test_sql_mem.py
python and modules 3928
connection 4048
empty cursor 4068
cursor after execute 4080
result -- (406500L,)
after fetchone 4088
cursor closed 4092
empty cursor 4092
cursor after execute 4092
result -- (6087, 'title', 15, '18', 'Sonzogno', 508126)
after fetchone 4092
cursor closed 4092
real 0m6.107s
user 0m0.080s
sys 0m0.076s
michele:~/tmp$
## with NAMED_CURSOR = 0
michele:~/tmp$ time python test_sql_mem.py
python and modules 3932
connection 4048
empty cursor 4068
cursor after execute 4080
result -- (406500L,)
after fetchone 4092
cursor closed 4092
empty cursor 4092
cursor after execute 58440
result -- (6087, 'title', 15, '18', 'Sonzogno', 508126)
after fetchone 58452
cursor closed 58452
real 0m11.499s
user 0m0.544s
sys 0m0.176s
michele:~/tmp$
> but its been my
> experience with virtually all database client libraries that as you
> fetch rows and discard them, you only pull as much as you fetch into
> memory. i.e. if you had a resultset of 4000 rows and just fetched 5
> rows, only 5 rows get pulled over the wire. thats definitely how the
> lower level APIs work
I'm with you, but my code show other results
> and it would be pretty bad if psycopg2 didnt maintain that behavior.
I'll send another email to the psycopg2 ml, with this results, and I'll
reply you in the near future.
Michele
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