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POSearch with index is slower than without index in pytables when the result is large
 

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  1. POSearch with index is slower than without index in pytables when the result is large
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    <p>The following code create a test hdf5 file:</p> <pre><code>from tables import * class KeyValue(IsDescription): key = StringCol(itemsize=30, dflt=" ", pos=0) # character String value = Int64Col(dflt=0, pos=1) f = open_file("keyvalue.h5", "w") kv = f.create_table("/", "keyvalues", KeyValue) import string import random for j in range(20): values = [] for i in xrange(100000): key = "".join(random.sample(string.uppercase, 5)) value = random.randint(0, 1000000) values.append((key, value)) kv.append(values) f.close() </code></pre> <p>Here is the speed test code:</p> <pre><code>f = open_file("keyvalue.h5", "a") kv = f.root.keyvalues kv.cols.value.remove_index() print "without index" %timeit a = kv.read_where('value &lt; 10') %timeit a = kv.read_where('value &lt; 1000') kv.cols.value.create_csindex() print "with index" %timeit a = kv.read_where('value &lt; 10') %timeit a = kv.read_where('value &lt; 1000') f.close() </code></pre> <p>the output is:</p> <pre><code>without index 10 loops, best of 3: 66.1 ms per loop 10 loops, best of 3: 109 ms per loop with index 10000 loops, best of 3: 164 µs per loop 10 loops, best of 3: 121 ms per loop </code></pre> <p>When query 'value &lt; 10', search with index is much faster than without index, but when query 'value &lt; 1000', it's slower than without index.</p> <p>I want to know how can this happen, and can you post the <code>timeit</code> result on your machine?</p>
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    1. USHYRY
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    1. CONote that your code samples seem to be in ipython, not pure python.
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      1. POSearch with index is slower than without index in pytables when the result is large
      1. USAnthony Scopatz
 

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