Python Gensim how to make WMD similarity run faster with multiprocessing

Question

I am trying to run gensim WMD similarity faster. Typically, this is what is in the docs: Example corpus:

    my_corpus = ["Human machine interface for lab abc computer applications",
>>>              "A survey of user opinion of computer system response time",
>>>              "The EPS user interface management system",
>>>              "System and human system engineering testing of EPS",
>>>              "Relation of user perceived response time to error measurement",
>>>              "The generation of random binary unordered trees",
>>>              "The intersection graph of paths in trees",
>>>              "Graph minors IV Widths of trees and well quasi ordering",
>>>              "Graph minors A survey"]

my_query = 'Human and artificial intelligence software programs'
my_tokenized_query =['human','artificial','intelligence','software','programs']

model = a trained word2Vec model on about 100,000 documents similar to my_corpus.
model = Word2Vec.load(word2vec_model)

---

from gensim import Word2Vec
from gensim.similarities import WmdSimilarity

def init_instance(my_corpus,model,num_best):
    instance = WmdSimilarity(my_corpus, model,num_best = 1)
    return instance
instance[my_tokenized_query]

the best matched document is "Human machine interface for lab abc computer applications" which is great.

However the function instance above takes an extremely long time. So I thought of breaking up the corpus into N parts and then doing WMD on each with num_best = 1, then at the end of it, the part with the max score will be the most similar.

    from multiprocessing import Process, Queue ,Manager

    def main( my_query,global_jobs,process_tmp):
        process_query = gensim.utils.simple_preprocess(my_query)

        def worker(num,process_query,return_dict):  
            instance=init_instance\
(my_corpus[num*chunk+1:num*chunk+chunk], model,1)
            x = instance[process_query][0][0]
            y = instance[process_query][0][1]
            return_dict[x] = y
        manager = Manager()
        return_dict = manager.dict()

        for num in range(num_workers):
            process_tmp = Process(target=worker, args=(num,process_query,return_dict))
            global_jobs.append(process_tmp)
            process_tmp.start()
        for proc in global_jobs:
            proc.join()

        return_dict = dict(return_dict)
        ind = max(return_dict.iteritems(), key=operator.itemgetter(1))[0]
        print corpus[ind]
        >>> "Graph minors A survey"

The problem I have with this is that, even though it outputs something, it doesn't give me a good similar query from my corpus even though it gets the max similarity of all the parts.

Am I doing something wrong?

Answer 1

Comment: chunk is a static variable: e.g. chunk = 600 ...

If you define chunk static, then you have to compute num_workers.

10001 / 600 = 16,6683333333 = 17 num_workers

It's common to use not more process than cores you have.
If you have 17 cores, that's ok.

cores are static, therefore you should:

num_workers = os.cpu_count()
chunk = chunksize(my_corpus, num_workers)

---

1. Not the same result, changed to:

   #process_query = gensim.utils.simple_preprocess(my_query)
   process_query = my_tokenized_query
   

2. All worker results Index 0..n.
   Therefore, return_dict[x] could be overwritten from last worker with same Index having lower value. The Index in return_dict is NOT the same as Index in my_corpus. Changed to:

   #return_dict[x] = y
   return_dict[ (num * chunk)+x ] = y
   

3. Using +1 in chunk size computing, will skip that first Document.
   I don't know how you compute chunk, consider this example:

   def chunksize(iterable, num_workers):
       c_size, extra = divmod(len(iterable), num_workers)
       if extra:
           c_size += 1
       if len(iterable) == 0:
           c_size = 0
       return c_size
   
   #Usage
   chunk = chunksize(my_corpus, num_workers)
   ...
   #my_corpus_chunk = my_corpus[num*chunk+1:num*chunk+chunk]
   my_corpus_chunk = my_corpus[num * chunk:(num+1) * chunk]
   

Results: 10 cycle, Tuple=(Index worker num=0, Index worker num=1)

With multiprocessing, with chunk=5:
02,09:(3, 8), 01,03:(3, 5):
System and human system engineering testing of EPS
04,06,07:(0, 8), 05,08:(0, 5), 10:(0, 7):
Human machine interface for lab abc computer applications

Without multiprocessing, with chunk=5:
01:(3, 6), 02:(3, 5), 05,08,10:(3, 7), 07,09:(3, 8):
System and human system engineering testing of EPS
03,04,06:(0, 5):
Human machine interface for lab abc computer applications

Without multiprocessing, without chunking:
01,02,03,04,06,07,08:(3, -1):
System and human system engineering testing of EPS
05,09,10:(0, -1):
Human machine interface for lab abc computer applications

Tested with Python: 3.4.2

Answer 2

Using Python 2.7: I used threading instead of multi-processing. In the WMD-Instance creation thread, I do something like this:

    wmd_instances = []
    if wmd_instance_count > len(wmd_corpus):
        wmd_instance_count = len(wmd_corpus)
    chunk_size = int(len(wmd_corpus) / wmd_instance_count)
    for i in range(0, wmd_instance_count):
        if i == wmd_instance_count -1:
            wmd_instance = WmdSimilarity(wmd_corpus[i*chunk_size:], wmd_model, num_results)
        else:
            wmd_instance = WmdSimilarity(wmd_corpus[i*chunk_size:chunk_size], wmd_model, num_results)
        wmd_instances.append(wmd_instance)
    wmd_logic.setWMDInstances(wmd_instances, chunk_size)

'wmd_instance_count' is the number of threads to use to search. I also remember the chunk-size. Then, when I want to search for something, I start "wmd_instance_count"-threads to search for and they return found sims:

def perform_query_for_job_on_instance(wmd_logic, wmd_instances, query, jobID, instance):
    wmd_instance = wmd_instances[instance]
    sims = wmd_instance[query]
    wmd_logic.set_mt_thread_result(jobID, instance, sims)

'wmd_logic' is the instance of a class that then does this:

def set_mt_thread_result(self, jobID, instance, sims):
    res = []
    #
    # We need to scale the found ids back to our complete corpus size...
    #
    for sim in sims:
        aSim = (int(sim[0] + (instance * self.chunk_size)), sim[1])
        res.append(aSim)

I know, the code isn't nice, but it works. It uses 'wmd_instance_count' threads to find results, I aggregate them and then choose the top-10 or something like that.

Hope this helps.