Mercurial > hg > nginx-site
annotate xml/en/docs/hash.xml @ 241:664b6b874da2
Removed superfluous link.
author | Ruslan Ermilov <ru@nginx.com> |
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date | Tue, 13 Dec 2011 20:33:29 +0000 |
parents | abb48e50ff7f |
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"> |
abb48e50ff7f
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2 |
abb48e50ff7f
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3 <article name="Setting Up Hashes" |
abb48e50ff7f
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4 link="/en/docs/hash.html" |
abb48e50ff7f
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5 lang="en"> |
abb48e50ff7f
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6 |
abb48e50ff7f
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7 <section> |
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8 |
abb48e50ff7f
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9 <para> |
abb48e50ff7f
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10 To quickly process static sets of data such as server names, |
abb48e50ff7f
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11 map directive's values, mime-types, names of request header strings, |
abb48e50ff7f
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12 nginx uses hash tables. |
abb48e50ff7f
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13 During the start and each re-configuration nginx picks out |
abb48e50ff7f
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14 minimally possible sizes of hash tables such that the bucket size |
abb48e50ff7f
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15 that stores keys with identical hash values does not exceed the |
abb48e50ff7f
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16 configured parameter (hash bucket size). |
abb48e50ff7f
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17 The size of the table is expressed in buckets. |
abb48e50ff7f
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18 The adjustment is continued until the table size exceeds the |
abb48e50ff7f
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19 hash max size parameter. |
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20 Most hashes have the corresponding directives that allow to change |
abb48e50ff7f
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21 these parameters, for example, for the server names hash they are |
abb48e50ff7f
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22 <link doc="http/ngx_http_core_module.xml" id="server_names_hash_max_size"/> |
abb48e50ff7f
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23 and <link doc="http/ngx_http_core_module.xml" id="server_names_hash_bucket_size"/>. |
abb48e50ff7f
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24 </para> |
abb48e50ff7f
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25 |
abb48e50ff7f
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26 <para> |
abb48e50ff7f
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27 The hash bucket size parameter is aligned to the size that is a |
abb48e50ff7f
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28 multiple of the processor's cache line size. This speeds up |
abb48e50ff7f
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29 key search in a hash on modern processors by reducing the number |
abb48e50ff7f
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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—first to compute the bucket address, |
abb48e50ff7f
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34 and second during the key search inside the bucket. |
abb48e50ff7f
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35 Therefore, if nginx emits the message requesting to increase |
abb48e50ff7f
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36 either hash max size or hash bucket size then the first parameter |
abb48e50ff7f
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37 should first be increased. |
abb48e50ff7f
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38 </para> |
abb48e50ff7f
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39 |
abb48e50ff7f
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40 </section> |
abb48e50ff7f
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41 |
abb48e50ff7f
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42 </article> |