2004-07-31 00:27:55 +00:00
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/************************************************************************
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* @file implementation of variable-sized slotted pages
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STRUCTURE OF A PAGE
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<pre>
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+-----------------------------------------+-----------------------+----+
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| DATA SECTION +--------->| RID: (PAGE, 0) | |
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| +-----------------+ | +-----------------------+ |
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| +-->| RID: (PAGE, 1) | | |
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| | +-----------------+ | |
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| | | |
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| ----------------+ | +------------------------------+
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| | | +--->| RID: (PAGE, n) |
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| | | | +------------------------------+
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|======================================================================|
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| ^ FREE SPACE | | | |
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| +-------------------|-------|---|--------------------+ |
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| | | | | |
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| +-------------|-------|---+ | |
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| | | | | |
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| +---|---+-----+---|---+---|---+--------------+-----|------+-------+
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| | slotn | ... | slot1 | slot0 | num of slots | free space | *** |
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+----+-------+-----+-------+-------+--------------+------------+-------+
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</pre>
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*** = @see page.h for information on this field.
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NOTE:
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- slots are zero indexed.
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- slots are of implemented as (offset, length)
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Slotted page layout:
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END:
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lsn (4 bytes)
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type (2 bytes)
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free space (2 bytes)
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num of slots (2 bytes)
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freelist head(2 bytes)
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slot 0 (4 bytes)
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slot 1 (4 bytes)
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...
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slot n (4 bytes)
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...
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unused
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...
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record n (x bytes)
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...
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record 0 (y bytes)
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record 1 (z bytes)
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START
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$Id$
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************************************************************************/
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#define SLOTTED_PAGE_OVERHEAD_PER_RECORD 4
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#define SLOTTED_PAGE_HEADER_OVERHEAD 6
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2004-07-30 01:28:39 +00:00
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void pageWriteRecord(int xid, Page * page, lsn_t lsn, recordid rid, const byte *data);
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void pageReadRecord(int xid, Page * page, recordid rid, byte *buff);
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/**
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* assumes that the page is already loaded in memory. It takes as a
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* parameter a Page, and returns an estimate of the amount of free space on this
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* page. This is either exact, or an underestimate.
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* @todo how should this be handled? */
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int freespace(Page * p);
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void pageInitialize(Page * p);
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#define freespace_ptr(page) shorts_from_end((page), 1)
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#define numslots_ptr(page) shorts_from_end((page), 2)
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#define freelist_ptr(page) shorts_from_end((page), 3)
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#define slot_ptr(page, n) shorts_from_end((page), (2*(n))+4)
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#define slot_length_ptr(page, n) shorts_from_end((page), (2*(n))+5)
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#define record_ptr(page, n) bytes_from_start((page), *slot_ptr((page), (n)))
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#define isValidSlot(page, n) ((*slot_ptr((page), (n)) == INVALID_SLOT) ? 0 : 1)
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