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https://github.com/haproxy/haproxy.git
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98634f0c7b
Summary:
In testing at tumblr, we found that using djb2 hashing instead of the
default sdbm hashing resulted is better workload distribution to our backends.
This commit implements a change, that allows the user to specify the hash
function they want to use. It does not limit itself to consistent hashing
scenarios.
The supported hash functions are sdbm (default), and djb2.
For a discussion of the feature and analysis, see mailing list thread
"Consistent hashing alternative to sdbm" :
http://marc.info/?l=haproxy&m=138213693909219
Note: This change does NOT make changes to new features, for instance,
applying an avalance hashing always being performed before applying
consistent hashing.
61 lines
1.7 KiB
C
61 lines
1.7 KiB
C
/*
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* Hash function implementation
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*
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* See mailing list thread on "Consistent hashing alternative to sdbm"
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* http://marc.info/?l=haproxy&m=138213693909219
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*
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* Copyright 2000-2010 Willy Tarreau <w@1wt.eu>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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*/
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#include <common/hash.h>
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unsigned long hash_djb2(const char *key, int len)
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{
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unsigned long hash = 5381;
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/* the hash unrolled eight times */
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for (; len >= 8; len -= 8) {
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hash = ((hash << 5) + hash) + *key++;
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hash = ((hash << 5) + hash) + *key++;
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hash = ((hash << 5) + hash) + *key++;
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hash = ((hash << 5) + hash) + *key++;
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hash = ((hash << 5) + hash) + *key++;
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hash = ((hash << 5) + hash) + *key++;
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hash = ((hash << 5) + hash) + *key++;
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hash = ((hash << 5) + hash) + *key++;
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}
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switch (len) {
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case 7: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
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case 6: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
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case 5: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
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case 4: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
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case 3: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
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case 2: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
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case 1: hash = ((hash << 5) + hash) + *key++; break;
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default: /* case 0: */ break;
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}
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return hash;
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}
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unsigned long hash_sdbm(const char *key, int len)
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{
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unsigned long hash = 0;
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int c;
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while (len--) {
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c = *key++;
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hash = c + (hash << 6) + (hash << 16) - hash;
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}
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return hash;
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}
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