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Commit2515882

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Modify PageIsEmpty and PageGetMaxOffsetNumber macros to behave sanely
if presented an uninitialized (all zeroes) page. The system no longercrashes hard if an all-zeroes page is present in a relation. There seemto be some boundary conditions where a page will be appended to a relationand zeroed, but its page header is never initialized; until we can trackdown and fix all of those, robustness seems like a good idea.Also, clean up some obsolete and downright wrong comments.
1 parentb79e75d commit2515882

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1 file changed

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‎src/include/storage/bufpage.h‎

Lines changed: 31 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
*
77
* Copyright (c) 1994, Regents of the University of California
88
*
9-
* $Id: bufpage.h,v 1.26 1999/07/16 17:07:37 momjian Exp $
9+
* $Id: bufpage.h,v 1.27 2000/01/08 21:59:55 tgl Exp $
1010
*
1111
*-------------------------------------------------------------------------
1212
*/
@@ -28,7 +28,7 @@
2828
* disk page is always a slotted page of the form:
2929
*
3030
* +----------------+---------------------------------+
31-
* | PageHeaderData |linp0linp1 linp2 ... |
31+
* | PageHeaderData | linp1 linp2 linp3 ... |
3232
* +-----------+----+---------------------------------+
3333
* | ... linpN | |
3434
* +-----------+--------------------------------------+
@@ -38,7 +38,7 @@
3838
* +-------------+------------------------------------+
3939
* | | tupleN ... |
4040
* +-------------+------------------+-----------------+
41-
* | ... tuple2 tuple1 tuple0 | "special space" |
41+
* | ...tuple3tuple2 tuple1 | "special space" |
4242
* +--------------------------------+-----------------+
4343
*^ pd_special
4444
*
@@ -58,17 +58,19 @@
5858
*
5959
* NOTES:
6060
*
61-
* linp0..N form an ItemId array. ItemPointers point into this array
62-
* rather than pointing directly to a tuple.
61+
* linp1..N form an ItemId array. ItemPointers point into this array
62+
* rather than pointing directly to a tuple. Note that OffsetNumbers
63+
* conventionally start at 1, not 0.
6364
*
64-
*tuple0..N are added "backwards" on the page. because a tuple's
65+
*tuple1..N are added "backwards" on the page. because a tuple's
6566
* ItemPointer points to its ItemId entry rather than its actual
6667
* byte-offset position, tuples can be physically shuffled on a page
6768
* whenever the need arises.
6869
*
6970
* AM-generic per-page information is kept in the pd_opaque field of
70-
* the PageHeaderData.(this is currently only the page size.)
71-
* AM-specific per-page data is kept in the area marked "special
71+
* the PageHeaderData.(Currently, only the page size is kept here.)
72+
*
73+
* AM-specific per-page data (if any) is kept in the area marked "special
7274
* space"; each AM has an "opaque" structure defined somewhere that is
7375
* stored as the page trailer.an access method should always
7476
* initialize its pages with PageInit and then set its own opaque
@@ -85,11 +87,8 @@
8587
/*
8688
* location (byte offset) within a page.
8789
*
88-
* note that this is actually limited to 2^13 because we have limited
89-
* ItemIdData.lp_off and ItemIdData.lp_len to 13 bits (see itemid.h).
90-
*
91-
* uint16 is still valid, but the limit has been raised to 15 bits.
92-
* 06 Jan 98 - darrenk
90+
* note that this is actually limited to 2^15 because we have limited
91+
* ItemIdData.lp_off and ItemIdData.lp_len to 15 bits (see itemid.h).
9392
*/
9493
typedefuint16LocationIndex;
9594

@@ -98,13 +97,11 @@ typedef uint16 LocationIndex;
9897
* space management information generic to any page
9998
*
10099
*od_pagesize- size in bytes.
101-
*in reality, we need at least 64B to fit the
100+
*Minimum possible page size is perhaps 64B to fit
102101
* page header, opaque space and a minimal tuple;
103-
* on the high end, we can only support pages up
104-
* to 8KB because lp_off/lp_len are 13 bits.
105-
*
106-
* see above comment. Now use 15 bits and pages
107-
* up to 32KB at your own risk.
102+
* of course, in reality you want it much bigger.
103+
* On the high end, we can only support pages up
104+
* to 32KB because lp_off/lp_len are 15 bits.
108105
*/
109106
typedefstructOpaqueData
110107
{
@@ -123,7 +120,7 @@ typedef struct PageHeaderData
123120
LocationIndexpd_upper;/* offset to end of free space */
124121
LocationIndexpd_special;/* offset to start of special space */
125122
OpaqueDatapd_opaque;/* AM-generic information */
126-
ItemIdDatapd_linp[1];/* linepointers */
123+
ItemIdDatapd_linp[1];/*beginning oflinepointer array */
127124
}PageHeaderData;
128125

129126
typedefPageHeaderData*PageHeader;
@@ -160,8 +157,8 @@ typedef enum
160157
*returns true iff no itemid has been allocated on the page
161158
*/
162159
#definePageIsEmpty(page) \
163-
(((PageHeader) (page))->pd_lower== \
164-
(sizeof(PageHeaderData) - sizeof(ItemIdData)) ? true : false)
160+
(((PageHeader) (page))->pd_lower<= \
161+
(sizeof(PageHeaderData) - sizeof(ItemIdData)))
165162

166163
/*
167164
* PageIsNew
@@ -175,7 +172,7 @@ typedef enum
175172
*Returns an item identifier of a page.
176173
*/
177174
#definePageGetItemId(page,offsetNumber) \
178-
((ItemId) (&((PageHeader) (page))->pd_linp[(-1) + (offsetNumber)]))
175+
((ItemId) (&((PageHeader) (page))->pd_linp[(offsetNumber) - 1]))
179176

180177
/* ----------------
181178
*macros to access opaque space
@@ -210,7 +207,7 @@ typedef enum
210207
*Sets the page size of a page.
211208
*/
212209
#definePageSetPageSize(page,size) \
213-
((PageHeader) (page))->pd_opaque.od_pagesize = (size)
210+
(((PageHeader) (page))->pd_opaque.od_pagesize = (size))
214211

215212
/* ----------------
216213
*page special data macros
@@ -244,7 +241,7 @@ typedef enum
244241
*Retrieves an item on the given page.
245242
*
246243
* Note:
247-
*This does change the status of any of the resources passed.
244+
*This doesnotchange the status of any of the resources passed.
248245
*The semantics may change in the future.
249246
*/
250247
#definePageGetItem(page,itemId) \
@@ -264,7 +261,7 @@ typedef enum
264261
*The buffer can be a raw disk block and need not contain a valid
265262
*(formatted) disk page.
266263
*/
267-
/* XXX dig out of buffer descriptor */
264+
/* XXXshoulddig out of buffer descriptor */
268265
#defineBufferGetPageSize(buffer) \
269266
( \
270267
AssertMacro(BufferIsValid(buffer)), \
@@ -280,17 +277,17 @@ typedef enum
280277
/*
281278
* PageGetMaxOffsetNumber
282279
*Returns the maximum offset number used by the given page.
280+
*Since offset numbers are 1-based, this is also the number
281+
*of items on the page.
283282
*
284-
*NOTE:The offset is invalid if the page isnon-empty.
285-
*Test whether PageIsEmpty before calling this routine
286-
*and/orusing its return value.
283+
*NOTE:to ensure sane behavior if the page isnot initialized
284+
*(pd_lower == 0), cast the unsigned values to int before dividing.
285+
*That way we get -1orso, not a huge positive number...
287286
*/
288287
#definePageGetMaxOffsetNumber(page) \
289-
( \
290-
(((PageHeader) (page))->pd_lower - \
291-
(sizeof(PageHeaderData) - sizeof(ItemIdData))) \
292-
/ sizeof(ItemIdData) \
293-
)
288+
(((int) (((PageHeader) (page))->pd_lower - \
289+
(sizeof(PageHeaderData) - sizeof(ItemIdData)))) \
290+
/ ((int) sizeof(ItemIdData)))
294291

295292

296293
/* ----------------------------------------------------------------

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