From 96b9984c7acddf12b7d289be91af2b4a67860e80 Mon Sep 17 00:00:00 2001 From: Andrey Borodin Date: Tue, 30 May 2017 15:16:14 +0500 Subject: [PATCH] Use primes for hashtable size We often use sizes equal to power of 2. This can be damaging for hashtable. I haven't found any mitigation for this in nginx code. So I made my own. For the explanation of problem see https://stackoverflow.com/questions/3980117/hash-table-why-size-should-be-prime I didn't tested this with nginx, code is checked only for correctness of ngx_hash_min_prime(). Also beware that I've changed state of paremeter hinit. I'm not sure this is acceptable. --- src/core/ngx_hash.c | 148 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 148 insertions(+) diff --git a/src/core/ngx_hash.c b/src/core/ngx_hash.c index 1944c7a21d..e49806c616 100644 --- a/src/core/ngx_hash.c +++ b/src/core/ngx_hash.c @@ -244,6 +244,153 @@ ngx_hash_find_combined(ngx_hash_combined_t *hash, ngx_uint_t key, u_char *name, return NULL; } +static ngx_uint_t ngx_hash_min_prime(ngx_uint_t value) { + static ngx_uint_t primes[] = + { + 3, + 7, + 11, + 17, + 23, + 29, + 37, + 47, + 59, + 71, + 89, + 107, + 131, + 163, + 197, + 239, + 293, + 353, + 431, + 521, + 631, + 761, + 919, + 1103, + 1327, + 1597, + 1931, + 2333, + 2801, + 3371, + 4049, + 4861, + 5839, + 7013, + 8419, + 10103, + 12143, + 14591, + 17519, + 21023, + 25229, + 30293, + 36353, + 43627, + 52361, + 62851, + 75431, + 90523, + 108631, + 130363, + 156437, + 187751, + 225307, + 270371, + 324449, + 389357, + 467237, + 560689, + 672827, + 807403, + 968897, + 1162687, + 1395263, + 1674319, + 2009191, + 2411033, + 2893249, + 3471899, + 4166287, + 4999559, + 5999471, + 7199369, + 7919311, + 8711267, + 9582409, + 10540661, + 11594729, + 12754219, + 14029643, + 15432619, + 16975891, + 18673483, + 20540831, + 22594919, + 24854419, + 27339863, + 30073853, + 33081239, + 36389369, + 40028333, + 44031179, + 48434303, + 53277769, + 58605563, + 64466147, + 70912783, + 78004061, + 85804471, + 94384919, + 103823417, + 114205771, + 125626351, + 138189017, + 152007971, + 167208817, + 183929719, + 202322693, + 222554977, + 244810487, + 269291537, + 296220709, + 325842779, + 358427071, + 394269781, + 433696759, + 477066449, + 524773133, + 577250461, + 634975519, + 698473099, + 768320467, + 845152513, + 929667799, + 1022634581, + 1124898043, + 1237387859, + 1361126671, + 1497239377, + 1646963321, + 1811659669, + 1992825643, + }; + + for (size_t i = 0; i < sizeof(primes)/sizeof(*primes); ++i) + { + ngx_uint_t prime = primes[i]; + if (prime >= value) + { + value = prime; + break; + } + } + return value; +} #define NGX_HASH_ELT_SIZE(name) \ (sizeof(void *) + ngx_align((name)->key.len + 2, sizeof(void *))) @@ -264,6 +411,7 @@ ngx_hash_init(ngx_hash_init_t *hinit, ngx_hash_key_t *names, ngx_uint_t nelts) hinit->name, hinit->name, hinit->max_size); return NGX_ERROR; } + hinit->max_size = ngx_hash_min_prime(hinit->max_size); for (n = 0; n < nelts; n++) { if (hinit->bucket_size < NGX_HASH_ELT_SIZE(&names[n]) + sizeof(void *))