Mercurial > hg > nginx-site
diff xml/en/docs/hash.xml @ 215:abb48e50ff7f
Translated the "Setting Up Hashes" article into English.
author | Ruslan Ermilov <ru@nginx.com> |
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date | Wed, 30 Nov 2011 09:20:55 +0000 |
parents | |
children | a1071d0d0979 |
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new file mode 100644 --- /dev/null +++ b/xml/en/docs/hash.xml @@ -0,0 +1,42 @@ +<!DOCTYPE article SYSTEM "../../../dtd/article.dtd"> + +<article name="Setting Up Hashes" + link="/en/docs/hash.html" + lang="en"> + +<section> + +<para> +To quickly process static sets of data such as server names, +map directive's values, mime-types, names of request header strings, +nginx uses hash tables. +During the start and each re-configuration nginx picks out +minimally possible sizes of hash tables such that the bucket size +that stores keys with identical hash values does not exceed the +configured parameter (hash bucket size). +The size of the table is expressed in buckets. +The adjustment is continued until the table size exceeds the +hash max size parameter. +Most hashes have the corresponding directives that allow to change +these parameters, for example, for the server names hash they are +<link doc="http/ngx_http_core_module.xml" id="server_names_hash_max_size"/> +and <link doc="http/ngx_http_core_module.xml" id="server_names_hash_bucket_size"/>. +</para> + +<para> +The hash bucket size parameter is aligned to the size that is a +multiple of the processor's cache line size. This speeds up +key search in a hash on modern processors by reducing the number +of memory accesses. +If hash bucket size is equal to one processor's cache line size +then the number of memory accesses during the key search will be +two in the worst case—first to compute the bucket address, +and second during the key search inside the bucket. +Therefore, if nginx emits the message requesting to increase +either hash max size or hash bucket size then the first parameter +should first be increased. +</para> + +</section> + +</article>