序列类型分析

结构定义

对数据库中类型为序列的字段进行操作的分析函数库使用在头文件 mcoseq.h 中定义的 mco_seq_iterator_t 结构，如下所示：

    typedef struct mco_seq_iterator_t_
    {
        mco_seq_iterator_next_t next; 		/* method for obtaning next portion of values */
        mco_seq_iterator_reset_t reset; 	/* start iteration from beginning */
        mco_seq_iterator_prepare_t prepare; /* prepare iterator (used to start parallel processing) */
        mco_seq_iterator_merge_t merge; 	/* merge two iterators (used to merge results of parallel processing) */
        uint2 elem_size; 			/* size of element */
        uint2 tile_size; 			/* number of tile items */
        uint2 tile_offs; 			/* offset to first not handled tile item */
        uint1 rle_offs;  			/* index within same RLE value */
        uint1 prepared;  			/* flag set by prepare function */
        mco_seq_no_t first_seq_no; 	/* first sequence number (inclusive) */
        mco_seq_no_t next_seq_no;  	/* sequence number of element returned by sudsequent invocation of next() function */
        mco_seq_no_t last_seq_no;  	/* last sequence number (inclusive) */
        struct mco_seq_iterator_t_* opd[3]; 	/*operands of sequence operator */
        void* buf; 					/* memory buffer used by operators requiring temporary memory (reverse, order_by) */
        mco_size_t buf_size; 		/* size of buffer */
        uint1 elem_type; 			/* result element type MCO_DD_... */
        uint1 bounded; 				/* iterator is used in expression */
        uint1 createdBySql; 		/* iterator was created by SQL */
        uint8 context[MCO_SEQ_ITERATOR_CTX_SIZE/8]; 	/* operator specific context */
        mco_seq_tile_t tile;  		/* tile of values */
     
    } mco_seq_iterator_t, *mco_seq_iterator_h;

诸如生成的函数 classname_fieldname_search() 这样的函数使用 mco_seq_boundary_kind_t 结构来指定边界类型：

    typedef enum mco_seq_boundary_kind_t_
    {
        MCO_SEQ_BOUNDARY_OPEN,
        MCO_SEQ_BOUNDARY_INCLUSIVE,
        MCO_SEQ_BOUNDARY_EXCLUSIVE
     
    } mco_seq_boundary_kind_t;

为了优化内存中序列的访问，序列函数在连续内存块中的序列值数组上运行。

用于此内部优化的 mco_seq_iterator_t 结构的最后一个元素层定义如下：

    typedef union mco_seq_tile_t_
    {
        mco_seq_bool 	arr_mco_seq_bool[MCO_SEQ_TILE_SIZE_BYTES/sizeof(mco_seq_bool)];
        char 	arr_char[MCO_SEQ_TILE_SIZE_BYTES];
        int1 	arr_int1[MCO_SEQ_TILE_SIZE_BYTES];
        int2 	arr_int2[MCO_SEQ_TILE_SIZE_BYTES/sizeof(int2)];
        int4 	arr_int4[MCO_SEQ_TILE_SIZE_BYTES/sizeof(int4)];
        mco_int8 	arr_int8[MCO_SEQ_TILE_SIZE_BYTES/sizeof(mco_int8)];
        uint1 	arr_uint1[MCO_SEQ_TILE_SIZE_BYTES/sizeof(uint1)];
        uint2 	arr_uint2[MCO_SEQ_TILE_SIZE_BYTES/sizeof(uint2)];
        uint4 	arr_uint4[MCO_SEQ_TILE_SIZE_BYTES/sizeof(uint4)];
        uint8 	arr_uint8[MCO_SEQ_TILE_SIZE_BYTES/sizeof(uint8)];
        mco_time 	arr_mco_time[MCO_SEQ_TILE_SIZE_BYTES/sizeof(mco_time)];
        mco_date 	arr_mco_date[MCO_SEQ_TILE_SIZE_BYTES/sizeof(mco_date)];
        mco_datetime 	arr_datetime[MCO_SEQ_TILE_SIZE_BYTES/sizeof(mco_datetime)];
        float 	arr_float[MCO_SEQ_TILE_SIZE_BYTES/sizeof(float)];
        double 	arr_double[MCO_SEQ_TILE_SIZE_BYTES/sizeof(double)];
     
    } mco_seq_tile_t MCO_ALIGN_16;