mirror of https://github.com/postgres/postgres
Modify PageIsEmpty and PageGetMaxOffsetNumber macros to behave sanely
if presented an uninitialized (all zeroes) page. The system no longer crashes hard if an all-zeroes page is present in a relation. There seem to be some boundary conditions where a page will be appended to a relation and zeroed, but its page header is never initialized; until we can track down and fix all of those, robustness seems like a good idea. Also, clean up some obsolete and downright wrong comments.
This commit is contained in:
Tom Lane
parent
b79e75d66f
commit
2515882a0f
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@ -6,7 +6,7 @@
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*
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* Copyright (c) 1994, Regents of the University of California
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*
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* $Id: bufpage.h,v 1.26 1999/07/16 17:07:37 momjian Exp $
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* $Id: bufpage.h,v 1.27 2000/01/08 21:59:55 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -28,7 +28,7 @@
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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 | linp0 linp1 linp2 ... |
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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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@ -38,7 +38,7 @@
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* +-------------+------------------------------------+
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* | | tupleN ... |
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* +-------------+------------------+-----------------+
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* | ... tuple2 tuple1 tuple0 | "special space" |
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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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@ -58,17 +58,19 @@
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*
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* NOTES:
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*
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* linp0..N form an ItemId array. ItemPointers point into this array
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* rather than pointing directly to a tuple.
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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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* tuple0..N are added "backwards" on the page. because a tuple's
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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 the pd_opaque field of
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* the PageHeaderData. (this is currently only the page size.)
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* AM-specific per-page data is kept in the area marked "special
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* the PageHeaderData. (Currently, only the page size is kept here.)
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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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@ -85,11 +87,8 @@
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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 2^13 because we have limited
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* ItemIdData.lp_off and ItemIdData.lp_len to 13 bits (see itemid.h).
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*
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* uint16 is still valid, but the limit has been raised to 15 bits.
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* 06 Jan 98 - darrenk
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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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@ -98,13 +97,11 @@ typedef uint16 LocationIndex;
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* space management information generic to any page
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*
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* od_pagesize - size in bytes.
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* in reality, we need at least 64B to fit the
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* Minimum possible page size is perhaps 64B to fit
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* page header, opaque space and a minimal tuple;
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* on the high end, we can only support pages up
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* to 8KB because lp_off/lp_len are 13 bits.
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*
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* see above comment. Now use 15 bits and pages
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* up to 32KB at your own risk.
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* of course, in reality you want it much bigger.
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* On the high end, we can only support pages up
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* to 32KB because lp_off/lp_len are 15 bits.
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*/
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typedef struct OpaqueData
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{
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@ -123,7 +120,7 @@ typedef struct PageHeaderData
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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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OpaqueData pd_opaque; /* AM-generic information */
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ItemIdData pd_linp[1]; /* line pointers */
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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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@ -160,8 +157,8 @@ typedef enum
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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 == \
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(sizeof(PageHeaderData) - sizeof(ItemIdData)) ? true : false)
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(((PageHeader) (page))->pd_lower <= \
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(sizeof(PageHeaderData) - sizeof(ItemIdData)))
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/*
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* PageIsNew
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@ -175,7 +172,7 @@ typedef enum
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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[(-1) + (offsetNumber)]))
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((ItemId) (&((PageHeader) (page))->pd_linp[(offsetNumber) - 1]))
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/* ----------------
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* macros to access opaque space
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@ -210,7 +207,7 @@ typedef enum
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* Sets the page size of a page.
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*/
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#define PageSetPageSize(page, size) \
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((PageHeader) (page))->pd_opaque.od_pagesize = (size)
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(((PageHeader) (page))->pd_opaque.od_pagesize = (size))
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/* ----------------
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* page special data macros
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@ -244,7 +241,7 @@ typedef enum
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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 change the status of any of the resources passed.
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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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@ -264,7 +261,7 @@ typedef enum
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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 dig out of buffer descriptor */
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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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@ -280,17 +277,17 @@ typedef enum
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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: The offset is invalid if the page is non-empty.
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* Test whether PageIsEmpty before calling this routine
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* and/or using its return value.
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* NOTE: to ensure sane behavior if the page is not initialized
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* (pd_lower == 0), cast the unsigned values to int before dividing.
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* That way we get -1 or so, not a huge positive number...
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*/
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#define PageGetMaxOffsetNumber(page) \
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( \
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(((PageHeader) (page))->pd_lower - \
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(sizeof(PageHeaderData) - sizeof(ItemIdData))) \
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/ sizeof(ItemIdData) \
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)
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(((int) (((PageHeader) (page))->pd_lower - \
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(sizeof(PageHeaderData) - sizeof(ItemIdData)))) \
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/ ((int) sizeof(ItemIdData)))
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/* ----------------------------------------------------------------
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