python - DynamoDB Parallel Scan not splitting results -

i'm using segment , totalsegments parameters split dynamodb scan on multiple workers (as shown in parallel scan section of developer guide).

however, of results returned 1 worker. issue here? there perhaps issue how i've implemented threading?

import threading import boto3  def scan_foo_table(foo, segment, total_segments):     print 'looking @ segment ' + str(segment)     session = boto3.session.session()     dynamodbclient = session.client('dynamodb')     response = dynamodbclient.scan(         tablename='footable',         filterexpression='bar=:bar',         expressionattributevalues={             ':bar': {'s': bar}         },         segment=segment,         totalsegments=total_segments,     )     print 'segment ' + str(segment) + ' returned ' + str(len(response['items'])) + ' items'  def create_threads(bar):     thread_list = []     total_threads = 3      in range(total_threads):         # instantiate , store thread         thread = threading.thread(target=scan_foo_table, args=(bar, i, total_threads))         thread_list.append(thread)      # start threads     thread in thread_list:         thread.start()      # block main thread until threads finished     thread in thread_list:         thread.join()  def lambda_handler(event, context):     create_threads('123') 

output:

looking @ segment 0 looking @ segment 1 looking @ segment 2 segment 1 returned 0 items segment 2 returned 0 items segment 0 returned 10000 items 

one thing jumps @ me filter expression.

it possible items match filter expression located in first segment.

it worth noting parallel scan doesn't split items, splits key-space searched items. think of dividing large highway multiple lanes. possible le cars in fast lane , won't see cars in other lanes.

though in case seems more filter expression causing 1 segment return items.