Mysql源码学习——没那么简单的Hash(8)

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     动态Hash的本质是Hash函数的设计，图中给出的动态hash函数只是论文中提到的一个例子。下面就具体解读下Mysql中的hash插入——my_hash_insert

my_hash_insert非深入解析

    首先给出my_hash_insert的源代码,代码在mysys/hash.c中。

my_bool my_hash_insert(HASH *info, const uchar *record)

{

    int flag;

    size_t idx,halfbuff,first_index;

    my_hash_value_type hash_nr;

    uchar *UNINIT_VAR(ptr_to_rec),*UNINIT_VAR(ptr_to_rec2);

    HASH_LINK *data,*empty,*UNINIT_VAR(gpos),*UNINIT_VAR(gpos2),*pos;

    if (HASH_UNIQUE & info->flags)

    {

        uchar *key= (uchar*) my_hash_key(info, record, &idx, 1);

        if (my_hash_search(info, key, idx))

            return(TRUE);               /* Duplicate entry */

    }

    flag=0;

    if (!(empty=(HASH_LINK*) alloc_dynamic(&info->array)))

        return(TRUE);               /* No more memory */

    data=dynamic_element(&info->array,0,HASH_LINK*);

    halfbuff= info->blength >> 1;

    idx=first_index=info->records-halfbuff;

    if (idx != info->records)                /* If some records */

    {

        do

        {

            pos=data+idx;

            hash_nr=rec_hashnr(info,pos->data);

            if (flag == 0)              /* First loop; Check if ok */

                if (my_hash_mask(hash_nr, info->blength, info->records) != first_index)

                    break;

            if (!(hash_nr & halfbuff))