diff options
Diffstat (limited to 'db2/common/db_shash.c')
| -rw-r--r-- | db2/common/db_shash.c | 82 |
1 files changed, 59 insertions, 23 deletions
diff --git a/db2/common/db_shash.c b/db2/common/db_shash.c index ab188f564f..3f48a55907 100644 --- a/db2/common/db_shash.c +++ b/db2/common/db_shash.c @@ -1,14 +1,14 @@ /*- * See the file LICENSE for redistribution information. * - * Copyright (c) 1996, 1997 + * Copyright (c) 1996, 1997, 1998 * Sleepycat Software. All rights reserved. */ #include "config.h" #ifndef lint -static const char sccsid[] = "@(#)db_shash.c 10.4 (Sleepycat) 1/8/98"; +static const char sccsid[] = "@(#)db_shash.c 10.9 (Sleepycat) 4/10/98"; #endif /* not lint */ #ifndef NO_SYSTEM_INCLUDES @@ -19,39 +19,75 @@ static const char sccsid[] = "@(#)db_shash.c 10.4 (Sleepycat) 1/8/98"; #include "shqueue.h" #include "common_ext.h" -/* Powers-of-2 and close-by prime number pairs. */ +/* + * Table of good hash values. 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. + */ static const struct { - u_int power; - u_int prime; + u_int32_t power; + u_int32_t prime; } list[] = { - { 64, 67}, - { 128, 131}, - { 256, 257}, - { 512, 521}, - {1024, 1031}, - {2048, 2053}, - {4096, 4099}, - {8192, 8191}, - {0, 0} + { 64, 67}, /* 2^6 */ + { 128, 131}, /* 2^7 */ + { 256, 257}, /* 2^8 */ + { 512, 521}, /* 2^9 */ + { 1024, 1031}, /* 2^10 */ + { 2048, 2053}, /* 2^11 */ + { 4096, 4099}, /* 2^12 */ + { 8192, 8191}, /* 2^13 */ + { 16384, 16381}, /* 2^14 */ + { 32768, 32771}, /* 2^15 */ + { 65536, 65537}, /* 2^16 */ + { 131072, 131071}, /* 2^17 */ + { 262144, 262147}, /* 2^18 */ + { 393216, 393209}, /* 2^18 + 2^18/2 */ + { 524288, 524287}, /* 2^19 */ + { 786432, 786431}, /* 2^19 + 2^19/2 */ + { 1048576, 1048573}, /* 2^20 */ + { 1572864, 1572869}, /* 2^20 + 2^20/2 */ + { 2097152, 2097169}, /* 2^21 */ + { 3145728, 3145721}, /* 2^21 + 2^21/2 */ + { 4194304, 4194301}, /* 2^22 */ + { 6291456, 6291449}, /* 2^22 + 2^22/2 */ + { 8388608, 8388617}, /* 2^23 */ + { 12582912, 12582917}, /* 2^23 + 2^23/2 */ + { 16777216, 16777213}, /* 2^24 */ + { 25165824, 25165813}, /* 2^24 + 2^24/2 */ + { 33554432, 33554393}, /* 2^25 */ + { 50331648, 50331653}, /* 2^25 + 2^25/2 */ + { 67108864, 67108859}, /* 2^26 */ + { 100663296, 100663291}, /* 2^26 + 2^26/2 */ + { 134217728, 134217757}, /* 2^27 */ + { 201326592, 201326611}, /* 2^27 + 2^27/2 */ + { 268435456, 268435459}, /* 2^28 */ + { 402653184, 402653189}, /* 2^28 + 2^28/2 */ + { 536870912, 536870909}, /* 2^29 */ + { 805306368, 805306357}, /* 2^29 + 2^29/2 */ + {1073741824, 1073741827}, /* 2^30 */ + {0, 0} }; /* * __db_tablesize -- * Choose a size for the hash table. * - * PUBLIC: int __db_tablesize __P((u_int)); + * PUBLIC: int __db_tablesize __P((u_int32_t)); */ int __db_tablesize(n_buckets) - u_int n_buckets; + u_int32_t n_buckets; { int i; /* - * We try to be clever about how big we make the hash tables. Pick - * a prime number close to the "suggested" number of elements that - * will be in the hash table. We shoot for minimum collisions (i.e. - * one element in each bucket). We use 64 as the minimum table size. + * 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 64 as the minimum hash table size. * * Ref: Sedgewick, Algorithms in C, "Hash Functions" */ @@ -73,14 +109,14 @@ __db_tablesize(n_buckets) * __db_hashinit -- * Initialize a hash table that resides in shared memory. * - * PUBLIC: void __db_hashinit __P((void *, int)); + * PUBLIC: void __db_hashinit __P((void *, u_int32_t)); */ void __db_hashinit(begin, nelements) void *begin; - int nelements; + u_int32_t nelements; { - int i; + u_int32_t i; SH_TAILQ_HEAD(hash_head) *headp; headp = (struct hash_head *)begin; |