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34 * @(#)page.h 8.2 (Berkeley) 5/31/94
39 * Definitions for hashing page file format.
43 * routines dealing with a data page
46 * +------------------------------+
47 * p | n | keyoff | datoff | keyoff |
48 * +------------+--------+--------+
49 * | datoff | free | ptr | --> |
50 * +--------+---------------------+
52 * +--------------+---------------+
53 * | <---- - - - | data |
54 * +--------+-----+----+----------+
55 * | key | data | key |
56 * +--------+----------+----------+
58 * Pointer to the free space is always: p[p[0] + 2]
59 * Amount of free space on the page is: p[p[0] + 1]
63 * How many bytes required for this pair?
64 * 2 shorts in the table at the top of the page + room for the
65 * key and room for the data
67 * We prohibit entering a pair on a page unless there is also room to append
68 * an overflow page. The reason for this it that you can get in a situation
69 * where a single key/data pair fits on a page, but you can't append an
70 * overflow page and later you'd have to split the key/data and handle like
72 * You might as well do this up front.
75 #define PAIRSIZE(K,D) (2*sizeof(u_int16_t) + (K)->size + (D)->size)
76 #define BIGOVERHEAD (4*sizeof(u_int16_t))
77 #define KEYSIZE(K) (4*sizeof(u_int16_t) + (K)->size);
78 #define OVFLSIZE (2*sizeof(u_int16_t))
79 #define FREESPACE(P) ((P)[(P)[0]+1])
80 #define OFFSET(P) ((P)[(P)[0]+2])
81 #define PAIRFITS(P,K,D) \
82 (((P)[2] >= REAL_KEY) && \
83 (PAIRSIZE((K),(D)) + OVFLSIZE) <= FREESPACE((P)))
84 #define PAGE_META(N) (((N)+3) * sizeof(u_int16_t))