【MogDB】在MogDB中引入murmurhash3算法

背景

前一篇写了在ORACLE中引入murmurhash3算法的函数，【ORACLE】在ORACLE中使用自定义C语言函数引入cityhash和murmurhash3算法
本篇把相同算法的函数也放到MogDB中，这样就可以在数据同步后，使用相同算法计算hash值，来比较两个数据库中的数据是否一致

C源码

#include "postgres.h"
#include "fmgr.h"
#include <stdint.h>
#include <string.h>

PG_MODULE_MAGIC;

// MurmurHash3 32-bit implementation
uint32_t MurmurHash3_x86_32(const void *key, int len, uint32_t seed) {
    const uint8_t *data = (const uint8_t *)key;
    const int nblocks = len / 4;
    uint32_t h1 = seed;
    const uint32_t c1 = 0xcc9e2d51;
    const uint32_t c2 = 0x1b873593;

    // Body
    const uint32_t *blocks = (const uint32_t *)(data + nblocks * 4);
    for (int i = -nblocks; i; i++) {
        uint32_t k1 = blocks[i];
        k1 *= c1;
        k1 = (k1 << 15) | (k1 >> (32 - 15));
        k1 *= c2;
        h1 ^= k1;
        h1 = (h1 << 13) | (h1 >> (32 - 13));
        h1 = h1 * 5 + 0xe6546b64;
    }

    // Tail
    const uint8_t *tail = (const uint8_t *)(data + nblocks * 4);
    uint32_t k1 = 0;
    switch (len & 3) {
        case 3:
            k1 ^= tail[2] << 16;
        case 2:
            k1 ^= tail[1] << 8;
        case 1:
            k1 ^= tail[0];
            k1 *= c1;
            k1 = (k1 << 15) | (k1 >> (32 - 15));
            k1 *= c2;
            h1 ^= k1;
    }

    // Finalization
    h1 ^= len;
    h1 ^= h1 >> 16;
    h1 *= 0x85ebca6b;
    h1 ^= h1 >> 13;
    h1 *= 0xc2b2ae35;
    h1 ^= h1 >> 16;

    return h1;
}

extern "C" Datum murmurhash3(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(murmurhash3);

Datum murmurhash3(PG_FUNCTION_ARGS) {
    text *input = PG_GETARG_TEXT_PP(0);
    size_t len = VARSIZE_ANY_EXHDR(input);
    const char *str = VARDATA_ANY(input);
    uint32_t seed = 42; // You can use any seed value
    uint32_t hash = MurmurHash3_x86_32(str, len, seed);
    PG_RETURN_INT32((int32_t)hash);
}

编译

建议在数据库安装用户下编译

g++ -shared -o murmurhash3_function.so -fPIC murmurhash3_function.c -I`pg_config --includedir-server` -I`pg_config --includedir`

cp murmurhash3_function.so `pg_config --pkglibdir`/proc_srclib/

数据库函数

CREATE or replace FUNCTION murmurhash3(text) RETURNS integer immutable authid current_user
AS 'murmurhash3_function.so', 'murmurhash3'
LANGUAGE C STRICT;