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performance front, but with feature freeze upon us I think it's time to drive a stake in the ground and say that this will be in 7.5. Alvaro Herrera, with some help from Tom Lane.
322 lines
9.6 KiB
C
322 lines
9.6 KiB
C
/*-------------------------------------------------------------------------
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*
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* bufpage.h
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* Standard POSTGRES buffer page definitions.
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*
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*
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* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.59 2004/07/01 00:51:43 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef BUFPAGE_H
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#define BUFPAGE_H
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#include "storage/buf.h"
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#include "storage/bufmgr.h"
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#include "storage/item.h"
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#include "storage/itemid.h"
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#include "storage/off.h"
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#include "access/xlog.h"
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/*
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* A postgres disk page is an abstraction layered on top of a postgres
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* disk block (which is simply a unit of i/o, see block.h).
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*
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* specifically, while a disk block can be unformatted, a postgres
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* disk page is always a slotted page of the form:
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*
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* +----------------+---------------------------------+
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* | PageHeaderData | linp1 linp2 linp3 ... |
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* +-----------+----+---------------------------------+
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* | ... linpN | |
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* +-----------+--------------------------------------+
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* | ^ pd_lower |
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* | |
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* | v pd_upper |
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* +-------------+------------------------------------+
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* | | tupleN ... |
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* +-------------+------------------+-----------------+
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* | ... tuple3 tuple2 tuple1 | "special space" |
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* +--------------------------------+-----------------+
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* ^ pd_special
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*
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* a page is full when nothing can be added between pd_lower and
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* pd_upper.
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*
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* all blocks written out by an access method must be disk pages.
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*
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* EXCEPTIONS:
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*
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* obviously, a page is not formatted before it is initialized with by
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* a call to PageInit.
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*
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* NOTES:
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*
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* linp1..N form an ItemId array. ItemPointers point into this array
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* rather than pointing directly to a tuple. Note that OffsetNumbers
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* conventionally start at 1, not 0.
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*
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* tuple1..N are added "backwards" on the page. because a tuple's
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* ItemPointer points to its ItemId entry rather than its actual
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* byte-offset position, tuples can be physically shuffled on a page
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* whenever the need arises.
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*
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* AM-generic per-page information is kept in PageHeaderData.
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*
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* AM-specific per-page data (if any) is kept in the area marked "special
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* space"; each AM has an "opaque" structure defined somewhere that is
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* stored as the page trailer. an access method should always
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* initialize its pages with PageInit and then set its own opaque
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* fields.
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*/
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typedef Pointer Page;
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/*
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* location (byte offset) within a page.
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*
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* note that this is actually limited to 2^15 because we have limited
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* ItemIdData.lp_off and ItemIdData.lp_len to 15 bits (see itemid.h).
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*/
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typedef uint16 LocationIndex;
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/*
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* disk page organization
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* space management information generic to any page
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*
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* pd_lower - offset to start of free space.
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* pd_upper - offset to end of free space.
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* pd_special - offset to start of special space.
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* pd_pagesize_version - size in bytes and page layout version number.
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*
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* The page version number and page size are packed together into a single
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* uint16 field. This is for historical reasons: before PostgreSQL 7.3,
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* there was no concept of a page version number, and doing it this way
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* lets us pretend that pre-7.3 databases have page version number zero.
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* We constrain page sizes to be multiples of 256, leaving the low eight
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* bits available for a version number.
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*
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* Minimum possible page size is perhaps 64B to fit page header, opaque space
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* and a minimal tuple; of course, in reality you want it much bigger, so
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* the constraint on pagesize mod 256 is not an important restriction.
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* On the high end, we can only support pages up to 32KB because lp_off/lp_len
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* are 15 bits.
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*/
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typedef struct PageHeaderData
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{
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/* XXX LSN is member of *any* block, not */
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/* only page-organized - 'll change later */
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XLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog */
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/* record for last change of this page */
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StartUpID pd_sui; /* SUI of last changes (currently it's */
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/* used by heap AM only) */
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LocationIndex pd_lower; /* offset to start of free space */
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LocationIndex pd_upper; /* offset to end of free space */
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LocationIndex pd_special; /* offset to start of special space */
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uint16 pd_pagesize_version;
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ItemIdData pd_linp[1]; /* beginning of line pointer array */
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} PageHeaderData;
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typedef PageHeaderData *PageHeader;
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/*
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* Page layout version number 0 is for pre-7.3 Postgres releases.
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* Releases 7.3 and 7.4 use 1, denoting a new HeapTupleHeader layout.
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* Release 7.5 changed the HeapTupleHeader layout again.
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*/
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#define PG_PAGE_LAYOUT_VERSION 2
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/* ----------------------------------------------------------------
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* page support macros
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* ----------------------------------------------------------------
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*/
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/*
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* PageIsValid
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* True iff page is valid.
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*/
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#define PageIsValid(page) PointerIsValid(page)
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/*
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* line pointer does not count as part of header
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*/
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#define SizeOfPageHeaderData (offsetof(PageHeaderData, pd_linp[0]))
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/*
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* PageIsEmpty
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* returns true iff no itemid has been allocated on the page
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*/
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#define PageIsEmpty(page) \
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(((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData)
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/*
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* PageIsNew
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* returns true iff page has not been initialized (by PageInit)
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*/
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#define PageIsNew(page) (((PageHeader) (page))->pd_upper == 0)
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/*
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* PageGetItemId
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* Returns an item identifier of a page.
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*/
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#define PageGetItemId(page, offsetNumber) \
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((ItemId) (&((PageHeader) (page))->pd_linp[(offsetNumber) - 1]))
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/*
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* PageGetContents
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* To be used in case the page does not contain item pointers.
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*/
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#define PageGetContents(page) \
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((char *) (&((PageHeader) (page))->pd_linp[0]))
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/* ----------------
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* macros to access page size info
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* ----------------
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*/
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/*
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* PageSizeIsValid
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* True iff the page size is valid.
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*/
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#define PageSizeIsValid(pageSize) ((pageSize) == BLCKSZ)
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/*
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* PageGetPageSize
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* Returns the page size of a page.
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*
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* this can only be called on a formatted page (unlike
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* BufferGetPageSize, which can be called on an unformatted page).
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* however, it can be called on a page that is not stored in a buffer.
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*/
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#define PageGetPageSize(page) \
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((Size) (((PageHeader) (page))->pd_pagesize_version & (uint16) 0xFF00))
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/*
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* PageGetPageLayoutVersion
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* Returns the page layout version of a page.
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*/
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#define PageGetPageLayoutVersion(page) \
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(((PageHeader) (page))->pd_pagesize_version & 0x00FF)
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/*
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* PageSetPageSizeAndVersion
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* Sets the page size and page layout version number of a page.
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*
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* We could support setting these two values separately, but there's
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* no real need for it at the moment.
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*/
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#define PageSetPageSizeAndVersion(page, size, version) \
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( \
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AssertMacro(((size) & 0xFF00) == (size)), \
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AssertMacro(((version) & 0x00FF) == (version)), \
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((PageHeader) (page))->pd_pagesize_version = (size) | (version) \
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)
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/* ----------------
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* page special data macros
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* ----------------
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*/
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/*
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* PageGetSpecialSize
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* Returns size of special space on a page.
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*/
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#define PageGetSpecialSize(page) \
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((uint16) (PageGetPageSize(page) - ((PageHeader)(page))->pd_special))
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/*
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* PageGetSpecialPointer
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* Returns pointer to special space on a page.
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*/
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#define PageGetSpecialPointer(page) \
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( \
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AssertMacro(PageIsValid(page)), \
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(char *) ((char *) (page) + ((PageHeader) (page))->pd_special) \
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)
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/*
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* PageGetItem
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* Retrieves an item on the given page.
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*
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* Note:
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* This does not change the status of any of the resources passed.
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* The semantics may change in the future.
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*/
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#define PageGetItem(page, itemId) \
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( \
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AssertMacro(PageIsValid(page)), \
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AssertMacro((itemId)->lp_flags & LP_USED), \
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(Item)(((char *)(page)) + (itemId)->lp_off) \
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)
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/*
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* BufferGetPageSize
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* Returns the page size within a buffer.
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*
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* Notes:
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* Assumes buffer is valid.
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*
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* The buffer can be a raw disk block and need not contain a valid
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* (formatted) disk page.
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*/
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/* XXX should dig out of buffer descriptor */
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#define BufferGetPageSize(buffer) \
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( \
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AssertMacro(BufferIsValid(buffer)), \
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(Size)BLCKSZ \
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)
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/*
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* BufferGetPage
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* Returns the page associated with a buffer.
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*/
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#define BufferGetPage(buffer) ((Page)BufferGetBlock(buffer))
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/*
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* PageGetMaxOffsetNumber
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* Returns the maximum offset number used by the given page.
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* Since offset numbers are 1-based, this is also the number
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* of items on the page.
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*
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* NOTE: if the page is not initialized (pd_lower == 0), we must
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* return zero to ensure sane behavior. Accept double evaluation
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* of the argument so that we can ensure this.
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*/
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#define PageGetMaxOffsetNumber(page) \
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(((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData ? 0 : \
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((((PageHeader) (page))->pd_lower - SizeOfPageHeaderData) \
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/ sizeof(ItemIdData)))
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#define PageGetLSN(page) \
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(((PageHeader) (page))->pd_lsn)
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#define PageSetLSN(page, lsn) \
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(((PageHeader) (page))->pd_lsn = (lsn))
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#define PageGetSUI(page) \
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(((PageHeader) (page))->pd_sui)
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#define PageSetSUI(page, sui) \
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(((PageHeader) (page))->pd_sui = (StartUpID) (sui))
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/* ----------------------------------------------------------------
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* extern declarations
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* ----------------------------------------------------------------
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*/
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extern void PageInit(Page page, Size pageSize, Size specialSize);
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extern bool PageHeaderIsValid(PageHeader page);
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extern OffsetNumber PageAddItem(Page page, Item item, Size size,
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OffsetNumber offsetNumber, ItemIdFlags flags);
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extern Page PageGetTempPage(Page page, Size specialSize);
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extern void PageRestoreTempPage(Page tempPage, Page oldPage);
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extern int PageRepairFragmentation(Page page, OffsetNumber *unused);
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extern Size PageGetFreeSpace(Page page);
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extern void PageIndexTupleDelete(Page page, OffsetNumber offset);
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#endif /* BUFPAGE_H */
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