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annotate xml/en/docs/hash.xml @ 215:abb48e50ff7f

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Translated the "Setting Up Hashes" article into English.
author Ruslan Ermilov <ru@nginx.com>
date Wed, 30 Nov 2011 09:20:55 +0000
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children a1071d0d0979
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abb48e50ff7f Translated the "Setting Up Hashes" article into English.
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1 <!DOCTYPE article SYSTEM "../../../dtd/article.dtd">
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2
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3 <article name="Setting Up Hashes"
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4 link="/en/docs/hash.html"
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5 lang="en">
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6
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7 <section>
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8
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9 <para>
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10 To quickly process static sets of data such as server names,
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11 map directive's values, mime-types, names of request header strings,
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12 nginx uses hash tables.
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13 During the start and each re-configuration nginx picks out
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14 minimally possible sizes of hash tables such that the bucket size
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15 that stores keys with identical hash values does not exceed the
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16 configured parameter (hash bucket size).
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17 The size of the table is expressed in buckets.
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18 The adjustment is continued until the table size exceeds the
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19 hash max size parameter.
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20 Most hashes have the corresponding directives that allow to change
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21 these parameters, for example, for the server names hash they are
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22 <link doc="http/ngx_http_core_module.xml" id="server_names_hash_max_size"/>
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23 and <link doc="http/ngx_http_core_module.xml" id="server_names_hash_bucket_size"/>.
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24 </para>
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25
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26 <para>
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27 The hash bucket size parameter is aligned to the size that is a
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28 multiple of the processor's cache line size. This speeds up
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29 key search in a hash on modern processors by reducing the number
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30 of memory accesses.
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31 If hash bucket size is equal to one processor's cache line size
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32 then the number of memory accesses during the key search will be
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33 two in the worst case&mdash;first to compute the bucket address,
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34 and second during the key search inside the bucket.
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35 Therefore, if nginx emits the message requesting to increase
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36 either hash max size or hash bucket size then the first parameter
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37 should first be increased.
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38 </para>
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39
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40 </section>
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41
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42 </article>