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/*-------------------------------------------------------------------------
*
* bufpage.h
* Standard POSTGRES buffer page definitions.
*
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/bufpage.h
*
*-------------------------------------------------------------------------
*/
#ifndef BUFPAGE_H
#define BUFPAGE_H
#include "access/xlogdefs.h"
#include "storage/block.h"
#include "storage/item.h"
#include "storage/off.h"
/*
* A postgres disk page is an abstraction layered on top of a postgres
* disk block (which is simply a unit of i/o, see block.h).
*
* specifically, while a disk block can be unformatted, a postgres
* disk page is always a slotted page of the form:
*
* +----------------+---------------------------------+
* | PageHeaderData | linp1 linp2 linp3 ... |
* +-----------+----+---------------------------------+
* | ... linpN | |
* +-----------+--------------------------------------+
* | ^ pd_lower |
* | |
* | v pd_upper |
* +-------------+------------------------------------+
* | | tupleN ... |
* +-------------+------------------+-----------------+
* | ... tuple3 tuple2 tuple1 | "special space" |
* +--------------------------------+-----------------+
* ^ pd_special
*
* a page is full when nothing can be added between pd_lower and
* pd_upper.
*
* all blocks written out by an access method must be disk pages.
*
* EXCEPTIONS:
*
* obviously, a page is not formatted before it is initialized by
* a call to PageInit.
*
* NOTES:
*
* linp1..N form an ItemId array. ItemPointers point into this array
* rather than pointing directly to a tuple. Note that OffsetNumbers
* conventionally start at 1, not 0.
*
* tuple1..N are added "backwards" on the page. because a tuple's
* ItemPointer points to its ItemId entry rather than its actual
* byte-offset position, tuples can be physically shuffled on a page
* whenever the need arises.
*
* AM-generic per-page information is kept in PageHeaderData.
*
* AM-specific per-page data (if any) is kept in the area marked "special
* space"; each AM has an "opaque" structure defined somewhere that is
* stored as the page trailer. an access method should always
* initialize its pages with PageInit and then set its own opaque
* fields.
*/
typedef Pointer Page;
/*
* location (byte offset) within a page.
*
* note that this is actually limited to 2^15 because we have limited
* ItemIdData.lp_off and ItemIdData.lp_len to 15 bits (see itemid.h).
*/
typedef uint16 LocationIndex;
/*
* For historical reasons, the 64-bit LSN value is stored as two 32-bit
* values.
*/
typedef struct
{
uint32 xlogid; /* high bits */
uint32 xrecoff; /* low bits */
} PageXLogRecPtr;
#define PageXLogRecPtrGet(val) \
((uint64) (val).xlogid << 32 | (val).xrecoff)
#define PageXLogRecPtrSet(ptr, lsn) \
((ptr).xlogid = (uint32) ((lsn) >> 32), (ptr).xrecoff = (uint32) (lsn))
/*
* disk page organization
*
* space management information generic to any page
*
* pd_lsn - identifies xlog record for last change to this page.
* pd_checksum - page checksum, if set.
* pd_flags - flag bits.
* pd_lower - offset to start of free space.
* pd_upper - offset to end of free space.
* pd_special - offset to start of special space.
* pd_pagesize_version - size in bytes and page layout version number.
* pd_prune_xid - oldest XID among potentially prunable tuples on page.
*
* The LSN is used by the buffer manager to enforce the basic rule of WAL:
* "thou shalt write xlog before data". A dirty buffer cannot be dumped
* to disk until xlog has been flushed at least as far as the page's LSN.
*
* pd_checksum stores the page checksum, if it has been set for this page;
* zero is a valid value for a checksum. If a checksum is not in use then
* we leave the field unset. This will typically mean the field is zero
* though non-zero values may also be present if databases have been
* pg_upgraded from releases prior to 9.3, when the same byte offset was
* used to store the current timelineid when the page was last updated.
* Note that there is no indication on a page as to whether the checksum
* is valid or not, a deliberate design choice which avoids the problem
* of relying on the page contents to decide whether to verify it. Hence
* there are no flag bits relating to checksums.
*
* pd_prune_xid is a hint field that helps determine whether pruning will be
* useful. It is currently unused in index pages.
*
* The page version number and page size are packed together into a single
* uint16 field. This is for historical reasons: before PostgreSQL 7.3,
* there was no concept of a page version number, and doing it this way
* lets us pretend that pre-7.3 databases have page version number zero.
* We constrain page sizes to be multiples of 256, leaving the low eight
* bits available for a version number.
*
* Minimum possible page size is perhaps 64B to fit page header, opaque space
* and a minimal tuple; of course, in reality you want it much bigger, so
* the constraint on pagesize mod 256 is not an important restriction.
* On the high end, we can only support pages up to 32KB because lp_off/lp_len
* are 15 bits.
*/
typedef struct PageHeaderData
{
/* XXX LSN is member of *any* block, not only page-organized ones */
PageXLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog
* record for last change to this page */
uint16 pd_checksum; /* checksum */
uint16 pd_flags; /* flag bits, see below */
LocationIndex pd_lower; /* offset to start of free space */
LocationIndex pd_upper; /* offset to end of free space */
LocationIndex pd_special; /* offset to start of special space */
uint16 pd_pagesize_version;
TransactionId pd_prune_xid; /* oldest prunable XID, or zero if none */
ItemIdData pd_linp[FLEXIBLE_ARRAY_MEMBER]; /* line pointer array */
} PageHeaderData;
typedef PageHeaderData *PageHeader;
/*
* pd_flags contains the following flag bits. Undefined bits are initialized
* to zero and may be used in the future.
*
* PD_HAS_FREE_LINES is set if there are any LP_UNUSED line pointers before
* pd_lower. This should be considered a hint rather than the truth, since
* changes to it are not WAL-logged.
*
* PD_PAGE_FULL is set if an UPDATE doesn't find enough free space in the
* page for its new tuple version; this suggests that a prune is needed.
* Again, this is just a hint.
*/
#define PD_HAS_FREE_LINES 0x0001 /* are there any unused line pointers? */
#define PD_PAGE_FULL 0x0002 /* not enough free space for new tuple? */
#define PD_ALL_VISIBLE 0x0004 /* all tuples on page are visible to
* everyone */
#define PD_VALID_FLAG_BITS 0x0007 /* OR of all valid pd_flags bits */
/*
* Page layout version number 0 is for pre-7.3 Postgres releases.
* Releases 7.3 and 7.4 use 1, denoting a new HeapTupleHeader layout.
* Release 8.0 uses 2; it changed the HeapTupleHeader layout again.
* Release 8.1 uses 3; it redefined HeapTupleHeader infomask bits.
* Release 8.3 uses 4; it changed the HeapTupleHeader layout again, and
* added the pd_flags field (by stealing some bits from pd_tli),
* as well as adding the pd_prune_xid field (which enlarges the header).
*
* As of Release 9.3, the checksum version must also be considered when
* handling pages.
*/
#define PG_PAGE_LAYOUT_VERSION 4
#define PG_DATA_CHECKSUM_VERSION 1
/* ----------------------------------------------------------------
* page support macros
* ----------------------------------------------------------------
*/
/*
* PageIsValid
* True iff page is valid.
*/
#define PageIsValid(page) PointerIsValid(page)
/*
* line pointer(s) do not count as part of header
*/
#define SizeOfPageHeaderData (offsetof(PageHeaderData, pd_linp))
/*
* PageIsEmpty
* returns true iff no itemid has been allocated on the page
*/
#define PageIsEmpty(page) \
(((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData)
/*
* PageIsNew
* returns true iff page has not been initialized (by PageInit)
*/
#define PageIsNew(page) (((PageHeader) (page))->pd_upper == 0)
/*
* PageGetItemId
* Returns an item identifier of a page.
*/
#define PageGetItemId(page, offsetNumber) \
((ItemId) (&((PageHeader) (page))->pd_linp[(offsetNumber) - 1]))
/*
* PageGetContents
* To be used in case the page does not contain item pointers.
*
* Note: prior to 8.3 this was not guaranteed to yield a MAXALIGN'd result.
* Now it is. Beware of old code that might think the offset to the contents
* is just SizeOfPageHeaderData rather than MAXALIGN(SizeOfPageHeaderData).
*/
#define PageGetContents(page) \
((char *) (page) + MAXALIGN(SizeOfPageHeaderData))
/* ----------------
* macros to access page size info
* ----------------
*/
/*
* PageSizeIsValid
* True iff the page size is valid.
*/
#define PageSizeIsValid(pageSize) ((pageSize) == BLCKSZ)
/*
* PageGetPageSize
* Returns the page size of a page.
*
* this can only be called on a formatted page (unlike
* BufferGetPageSize, which can be called on an unformatted page).
* however, it can be called on a page that is not stored in a buffer.
*/
#define PageGetPageSize(page) \
((Size) (((PageHeader) (page))->pd_pagesize_version & (uint16) 0xFF00))
/*
* PageGetPageLayoutVersion
* Returns the page layout version of a page.
*/
#define PageGetPageLayoutVersion(page) \
(((PageHeader) (page))->pd_pagesize_version & 0x00FF)
/*
* PageSetPageSizeAndVersion
* Sets the page size and page layout version number of a page.
*
* We could support setting these two values separately, but there's
* no real need for it at the moment.
*/
#define PageSetPageSizeAndVersion(page, size, version) \
( \
AssertMacro(((size) & 0xFF00) == (size)), \
AssertMacro(((version) & 0x00FF) == (version)), \
((PageHeader) (page))->pd_pagesize_version = (size) | (version) \
)
/* ----------------
* page special data macros
* ----------------
*/
/*
* PageGetSpecialSize
* Returns size of special space on a page.
*/
#define PageGetSpecialSize(page) \
((uint16) (PageGetPageSize(page) - ((PageHeader)(page))->pd_special))
/*
* Using assertions, validate that the page special pointer is OK.
*
* This is intended to catch use of the pointer before page initialization.
* It is implemented as a function due to the limitations of the MSVC
* compiler, which choked on doing all these tests within another macro. We
* return true so that MacroAssert() can be used while still getting the
* specifics from the macro failure within this function.
*/
static inline bool
PageValidateSpecialPointer(Page page)
{
Assert(PageIsValid(page));
Assert(((PageHeader) (page))->pd_special <= BLCKSZ);
Assert(((PageHeader) (page))->pd_special >= SizeOfPageHeaderData);
return true;
}
/*
* PageGetSpecialPointer
* Returns pointer to special space on a page.
*/
#define PageGetSpecialPointer(page) \
( \
AssertMacro(PageValidateSpecialPointer(page)), \
(char *) ((char *) (page) + ((PageHeader) (page))->pd_special) \
)
/*
* PageGetItem
* Retrieves an item on the given page.
*
* Note:
* This does not change the status of any of the resources passed.
* The semantics may change in the future.
*/
#define PageGetItem(page, itemId) \
( \
AssertMacro(PageIsValid(page)), \
AssertMacro(ItemIdHasStorage(itemId)), \
(Item)(((char *)(page)) + ItemIdGetOffset(itemId)) \
)
/*
* PageGetMaxOffsetNumber
* Returns the maximum offset number used by the given page.
* Since offset numbers are 1-based, this is also the number
* of items on the page.
*
* NOTE: if the page is not initialized (pd_lower == 0), we must
* return zero to ensure sane behavior. Accept double evaluation
* of the argument so that we can ensure this.
*/
#define PageGetMaxOffsetNumber(page) \
(((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData ? 0 : \
((((PageHeader) (page))->pd_lower - SizeOfPageHeaderData) \
/ sizeof(ItemIdData)))
/*
* Additional macros for access to page headers. (Beware multiple evaluation
* of the arguments!)
*/
#define PageGetLSN(page) \
PageXLogRecPtrGet(((PageHeader) (page))->pd_lsn)
#define PageSetLSN(page, lsn) \
PageXLogRecPtrSet(((PageHeader) (page))->pd_lsn, lsn)
#define PageHasFreeLinePointers(page) \
(((PageHeader) (page))->pd_flags & PD_HAS_FREE_LINES)
#define PageSetHasFreeLinePointers(page) \
(((PageHeader) (page))->pd_flags |= PD_HAS_FREE_LINES)
#define PageClearHasFreeLinePointers(page) \
(((PageHeader) (page))->pd_flags &= ~PD_HAS_FREE_LINES)
#define PageIsFull(page) \
(((PageHeader) (page))->pd_flags & PD_PAGE_FULL)
#define PageSetFull(page) \
(((PageHeader) (page))->pd_flags |= PD_PAGE_FULL)
#define PageClearFull(page) \
(((PageHeader) (page))->pd_flags &= ~PD_PAGE_FULL)
#define PageIsAllVisible(page) \
(((PageHeader) (page))->pd_flags & PD_ALL_VISIBLE)
#define PageSetAllVisible(page) \
(((PageHeader) (page))->pd_flags |= PD_ALL_VISIBLE)
#define PageClearAllVisible(page) \
(((PageHeader) (page))->pd_flags &= ~PD_ALL_VISIBLE)
#define PageIsPrunable(page, oldestxmin) \
( \
AssertMacro(TransactionIdIsNormal(oldestxmin)), \
TransactionIdIsValid(((PageHeader) (page))->pd_prune_xid) && \
TransactionIdPrecedes(((PageHeader) (page))->pd_prune_xid, oldestxmin) \
)
#define PageSetPrunable(page, xid) \
do { \
Assert(TransactionIdIsNormal(xid)); \
if (!TransactionIdIsValid(((PageHeader) (page))->pd_prune_xid) || \
TransactionIdPrecedes(xid, ((PageHeader) (page))->pd_prune_xid)) \
((PageHeader) (page))->pd_prune_xid = (xid); \
} while (0)
#define PageClearPrunable(page) \
(((PageHeader) (page))->pd_prune_xid = InvalidTransactionId)
/* ----------------------------------------------------------------
* extern declarations
* ----------------------------------------------------------------
*/
#define PAI_OVERWRITE (1 << 0)
#define PAI_IS_HEAP (1 << 1)
#define PageAddItem(page, item, size, offsetNumber, overwrite, is_heap) \
PageAddItemExtended(page, item, size, offsetNumber, \
((overwrite) ? PAI_OVERWRITE : 0) | \
((is_heap) ? PAI_IS_HEAP : 0))
extern void PageInit(Page page, Size pageSize, Size specialSize);
extern bool PageIsVerified(Page page, BlockNumber blkno);
extern OffsetNumber PageAddItemExtended(Page page, Item item, Size size,
OffsetNumber offsetNumber, int flags);
extern Page PageGetTempPage(Page page);
extern Page PageGetTempPageCopy(Page page);
extern Page PageGetTempPageCopySpecial(Page page);
extern void PageRestoreTempPage(Page tempPage, Page oldPage);
extern void PageRepairFragmentation(Page page);
extern Size PageGetFreeSpace(Page page);
extern Size PageGetFreeSpaceForMultipleTuples(Page page, int ntups);
extern Size PageGetExactFreeSpace(Page page);
extern Size PageGetHeapFreeSpace(Page page);
extern void PageIndexTupleDelete(Page page, OffsetNumber offset);
extern void PageIndexMultiDelete(Page page, OffsetNumber *itemnos, int nitems);
extern void PageIndexTupleDeleteNoCompact(Page page, OffsetNumber offset);
extern bool PageIndexTupleOverwrite(Page page, OffsetNumber offnum,
Item newtup, Size newsize);
extern char *PageSetChecksumCopy(Page page, BlockNumber blkno);
extern void PageSetChecksumInplace(Page page, BlockNumber blkno);
#endif /* BUFPAGE_H */