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POCannot grok python multiprocessing
 

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    <p>I need to run a function for the each of the elements of my database. </p> <p>When I try the following:</p> <pre><code>from multiprocessing import Pool from pymongo import Connection def foo(): ... connection1 = Connection('127.0.0.1', 27017) db1 = connection1.data my_pool = Pool(6) my_pool.map(foo, db1.index.find()) </code></pre> <p>I'm getting the following error: </p> <blockquote> <p>Job 1, 'python myscript.py ' terminated by signal SIGKILL (Forced quit)</p> </blockquote> <p>Which is, I think, caused by <code>db1.index.find()</code> eating all the available ram while trying to return millions of database elements... </p> <p>How should I modify my code for it to work? </p> <p>Some logs are here:</p> <pre><code>dmesg | tail -500 | grep memory [177886.768927] Out of memory: Kill process 3063 (python) score 683 or sacrifice child [177891.001379] [&lt;ffffffff8110e51a&gt;] out_of_memory+0xfa/0x250 [177891.021362] Out of memory: Kill process 3063 (python) score 684 or sacrifice child [177891.025399] [&lt;ffffffff8110e51a&gt;] out_of_memory+0xfa/0x250 </code></pre> <p>The actual function below:</p> <pre><code>def create_barrel(item): connection = Connection('127.0.0.1', 27017) db = connection.data print db.index.count() barrel = [] fls = [] if 'name' in item.keys(): barrel.append(WhitespaceTokenizer().tokenize(item['name'])) name = item['name'] elif 'name.utf-8' in item.keys(): barrel.append(WhitespaceTokenizer().tokenize(item['name.utf-8'])) name = item['name.utf-8'] else: print item.keys() if 'files' in item.keys(): for file in item['files']: if 'path' in file.keys(): barrel.append(WhitespaceTokenizer().tokenize(" ".join(file['path']))) fls.append(("\\".join(file['path']),file['length'])) elif 'path.utf-8' in file.keys(): barrel.append(WhitespaceTokenizer().tokenize(" ".join(file['path.utf-8']))) fls.append(("\\".join(file['path.utf-8']),file['length'])) else: print file barrel.append(WhitespaceTokenizer().tokenize(file)) if len(fls) &lt; 1: fls.append((name,item['length'])) barrel = sum(barrel,[]) for s in barrel: vs = re.findall("\d[\d|\.]*\d", s) #versions i.e. numbes such as 4.2.7500 b0 = [] for s in barrel: b0.append(re.split("[" + string.punctuation + "]", s)) b1 = filter(lambda x: x not in string.punctuation, sum(b0,[])) flag = True while flag: bb = [] flag = False for bt in b1: if bt[0] in string.punctuation: bb.append(bt[1:]) flag = True elif bt[-1] in string.punctuation: bb.append(bt[:-1]) flag = True else: bb.append(bt) b1 = bb b2 = b1 + barrel + vs b3 = list(set(b2)) b4 = map(lambda x: x.lower(), b3) b_final = {} b_final['_id'] = item['_id'] b_final['tags'] = b4 b_final['name'] = name b_final['files'] = fls print db.barrels.insert(b_final) </code></pre> <p>I've noticed interesting thing. Then I press ctrl+c to stop process I'm getting the following:</p> <pre><code>python index2barrel.py Traceback (most recent call last): File "index2barrel.py", line 83, in &lt;module&gt; my_pool.map(create_barrel, db1.index.find, 6) File "/usr/lib/python2.7/multiprocessing/pool.py", line 227, in map return self.map_async(func, iterable, chunksize).get() File "/usr/lib/python2.7/multiprocessing/pool.py", line 280, in map_async iterable = list(iterable) TypeError: 'instancemethod' object is not iterable </code></pre> <p>I mean, why multiprocessing is trying to convert somethin to the list? Isn't it the source of the problem? </p> <p>from the stack trace:</p> <pre><code>brk(0x231ccf000) = 0x231ccf000 futex(0x1abb150, FUTEX_WAKE_PRIVATE, 1) = 1 sendto(3, "+\0\0\0\260\263\355\356\0\0\0\0\325\7\0\0\0\0\0\0data.index\0\0"..., 43, 0, NULL, 0) = 43 recvfrom(3, "Some text from my database."..., 491663, 0, NULL, NULL) = 491663 ... [manymany times] brk(0x2320d5000) = 0x2320d5000 .... manymany times </code></pre> <p>The above sample goes and goes in strace output and for some reason strace -o logfile python myscript.py does not halt. It just eats all the available ram and writes in log file. </p> <p>UPDATE. Using imap instead of map solved my problem.</p>
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    1. COThis is Linux, yes? Do you have anything in the system logs showing the OOM killer terminated your process?
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    2. CO@cha0site Yes, this is ubuntu. I will examine the logs, but from htop I saw that memory (all the 8 GBs!) was eaten in a few seconds so I think the problem is the map(...) trying to get the whole database in list. Don't how to avoid this.
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    3. COI think we may need to see what `foo()` does. `find()` returns a `Cursor`, which shouldn't store all the records in memory...
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