/*- * See the file LICENSE for redistribution information. * * Copyright (c) 1996,2007 Oracle. All rights reserved. * * \$Id: db_shash.c,v 12.7 2007/05/17 15:14:55 bostic Exp \$ */ #include "db_config.h" #include "db_int.h" /* * __db_tablesize -- * Choose a size for the hash table. * * PUBLIC: u_int32_t __db_tablesize __P((u_int32_t)); */ u_int32_t __db_tablesize(n_buckets) u_int32_t n_buckets; { /* * We try to be clever about how big we make the hash tables. Use a * prime number close to the "suggested" number of elements that will * be in the hash table. Use 32 as the minimum hash table size. * * Ref: Sedgewick, Algorithms in C, "Hash Functions" * * Up to ~250,000 buckets, we use powers of 2. After that, we slow * the rate of increase by half. For each choice, we then use a * nearby prime number as the hash value. * * If a terabyte is the maximum cache we'll see, and we assume there * are 10 1K buckets on each hash chain, then 107374182 is the maximum * number of buckets we'll ever need. * * We don't use the obvious static data structure because some C * compilers (and I use the term loosely), can't handle them. */ #define HASH_SIZE(power, prime) { \ if ((power) >= n_buckets) \ return (prime); \ } HASH_SIZE(32, 37); /* 2^5 */ HASH_SIZE(64, 67); /* 2^6 */ HASH_SIZE(128, 131); /* 2^7 */ HASH_SIZE(256, 257); /* 2^8 */ HASH_SIZE(512, 521); /* 2^9 */ HASH_SIZE(1024, 1031); /* 2^10 */ HASH_SIZE(2048, 2053); /* 2^11 */ HASH_SIZE(4096, 4099); /* 2^12 */ HASH_SIZE(8192, 8191); /* 2^13 */ HASH_SIZE(16384, 16381); /* 2^14 */ HASH_SIZE(32768, 32771); /* 2^15 */ HASH_SIZE(65536, 65537); /* 2^16 */ HASH_SIZE(131072, 131071); /* 2^17 */ HASH_SIZE(262144, 262147); /* 2^18 */ HASH_SIZE(393216, 393209); /* 2^18 + 2^18/2 */ HASH_SIZE(524288, 524287); /* 2^19 */ HASH_SIZE(786432, 786431); /* 2^19 + 2^19/2 */ HASH_SIZE(1048576, 1048573); /* 2^20 */ HASH_SIZE(1572864, 1572869); /* 2^20 + 2^20/2 */ HASH_SIZE(2097152, 2097169); /* 2^21 */ HASH_SIZE(3145728, 3145721); /* 2^21 + 2^21/2 */ HASH_SIZE(4194304, 4194301); /* 2^22 */ HASH_SIZE(6291456, 6291449); /* 2^22 + 2^22/2 */ HASH_SIZE(8388608, 8388617); /* 2^23 */ HASH_SIZE(12582912, 12582917); /* 2^23 + 2^23/2 */ HASH_SIZE(16777216, 16777213); /* 2^24 */ HASH_SIZE(25165824, 25165813); /* 2^24 + 2^24/2 */ HASH_SIZE(33554432, 33554393); /* 2^25 */ HASH_SIZE(50331648, 50331653); /* 2^25 + 2^25/2 */ HASH_SIZE(67108864, 67108859); /* 2^26 */ HASH_SIZE(100663296, 100663291); /* 2^26 + 2^26/2 */ HASH_SIZE(134217728, 134217757); /* 2^27 */ HASH_SIZE(201326592, 201326611); /* 2^27 + 2^27/2 */ HASH_SIZE(268435456, 268435459); /* 2^28 */ HASH_SIZE(402653184, 402653189); /* 2^28 + 2^28/2 */ HASH_SIZE(536870912, 536870909); /* 2^29 */ HASH_SIZE(805306368, 805306357); /* 2^29 + 2^29/2 */ HASH_SIZE(1073741824, 1073741827); /* 2^30 */ return (1073741827); } /* * __db_hashinit -- * Initialize a hash table that resides in shared memory. * * PUBLIC: void __db_hashinit __P((void *, u_int32_t)); */ void __db_hashinit(begin, nelements) void *begin; u_int32_t nelements; { u_int32_t i; SH_TAILQ_HEAD(hash_head) *headp; headp = (struct hash_head *)begin; for (i = 0; i < nelements; i++, headp++) SH_TAILQ_INIT(headp); }