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comparison xml/en/docs/hash.xml @ 215:abb48e50ff7f
Translated the "Setting Up Hashes" article into English.
| author | Ruslan Ermilov <ru@nginx.com> |
|---|---|
| date | Wed, 30 Nov 2011 09:20:55 +0000 |
| parents | |
| children | a1071d0d0979 |
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| 214:c99c8df86eb9 | 215:abb48e50ff7f |
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| 1 <!DOCTYPE article SYSTEM "../../../dtd/article.dtd"> | |
| 2 | |
| 3 <article name="Setting Up Hashes" | |
| 4 link="/en/docs/hash.html" | |
| 5 lang="en"> | |
| 6 | |
| 7 <section> | |
| 8 | |
| 9 <para> | |
| 10 To quickly process static sets of data such as server names, | |
| 11 map directive's values, mime-types, names of request header strings, | |
| 12 nginx uses hash tables. | |
| 13 During the start and each re-configuration nginx picks out | |
| 14 minimally possible sizes of hash tables such that the bucket size | |
| 15 that stores keys with identical hash values does not exceed the | |
| 16 configured parameter (hash bucket size). | |
| 17 The size of the table is expressed in buckets. | |
| 18 The adjustment is continued until the table size exceeds the | |
| 19 hash max size parameter. | |
| 20 Most hashes have the corresponding directives that allow to change | |
| 21 these parameters, for example, for the server names hash they are | |
| 22 <link doc="http/ngx_http_core_module.xml" id="server_names_hash_max_size"/> | |
| 23 and <link doc="http/ngx_http_core_module.xml" id="server_names_hash_bucket_size"/>. | |
| 24 </para> | |
| 25 | |
| 26 <para> | |
| 27 The hash bucket size parameter is aligned to the size that is a | |
| 28 multiple of the processor's cache line size. This speeds up | |
| 29 key search in a hash on modern processors by reducing the number | |
| 30 of memory accesses. | |
| 31 If hash bucket size is equal to one processor's cache line size | |
| 32 then the number of memory accesses during the key search will be | |
| 33 two in the worst case—first to compute the bucket address, | |
| 34 and second during the key search inside the bucket. | |
| 35 Therefore, if nginx emits the message requesting to increase | |
| 36 either hash max size or hash bucket size then the first parameter | |
| 37 should first be increased. | |
| 38 </para> | |
| 39 | |
| 40 </section> | |
| 41 | |
| 42 </article> |