From 2515882a0fdbb0064a426621903eb99f425a7575 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sat, 8 Jan 2000 21:59:55 +0000 Subject: [PATCH] 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. --- src/include/storage/bufpage.h | 65 +++++++++++++++++------------------ 1 file changed, 31 insertions(+), 34 deletions(-) diff --git a/src/include/storage/bufpage.h b/src/include/storage/bufpage.h index c7688e4ae1..e0d85db452 100644 --- a/src/include/storage/bufpage.h +++ b/src/include/storage/bufpage.h @@ -6,7 +6,7 @@ * * Copyright (c) 1994, Regents of the University of California * - * $Id: bufpage.h,v 1.26 1999/07/16 17:07:37 momjian Exp $ + * $Id: bufpage.h,v 1.27 2000/01/08 21:59:55 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -28,7 +28,7 @@ * disk page is always a slotted page of the form: * * +----------------+---------------------------------+ - * | PageHeaderData | linp0 linp1 linp2 ... | + * | PageHeaderData | linp1 linp2 linp3 ... | * +-----------+----+---------------------------------+ * | ... linpN | | * +-----------+--------------------------------------+ @@ -38,7 +38,7 @@ * +-------------+------------------------------------+ * | | tupleN ... | * +-------------+------------------+-----------------+ - * | ... tuple2 tuple1 tuple0 | "special space" | + * | ... tuple3 tuple2 tuple1 | "special space" | * +--------------------------------+-----------------+ * ^ pd_special * @@ -58,17 +58,19 @@ * * NOTES: * - * linp0..N form an ItemId array. ItemPointers point into this array - * rather than pointing directly to a tuple. + * 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. * - * tuple0..N are added "backwards" on the page. because a tuple's + * 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 the pd_opaque field of - * the PageHeaderData. (this is currently only the page size.) - * AM-specific per-page data is kept in the area marked "special + * the PageHeaderData. (Currently, only the page size is kept here.) + * + * 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 @@ -85,11 +87,8 @@ /* * location (byte offset) within a page. * - * note that this is actually limited to 2^13 because we have limited - * ItemIdData.lp_off and ItemIdData.lp_len to 13 bits (see itemid.h). - * - * uint16 is still valid, but the limit has been raised to 15 bits. - * 06 Jan 98 - darrenk + * 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; @@ -98,13 +97,11 @@ typedef uint16 LocationIndex; * space management information generic to any page * * od_pagesize - size in bytes. - * in reality, we need at least 64B to fit the + * Minimum possible page size is perhaps 64B to fit * page header, opaque space and a minimal tuple; - * on the high end, we can only support pages up - * to 8KB because lp_off/lp_len are 13 bits. - * - * see above comment. Now use 15 bits and pages - * up to 32KB at your own risk. + * of course, in reality you want it much bigger. + * On the high end, we can only support pages up + * to 32KB because lp_off/lp_len are 15 bits. */ typedef struct OpaqueData { @@ -123,7 +120,7 @@ typedef struct PageHeaderData LocationIndex pd_upper; /* offset to end of free space */ LocationIndex pd_special; /* offset to start of special space */ OpaqueData pd_opaque; /* AM-generic information */ - ItemIdData pd_linp[1]; /* line pointers */ + ItemIdData pd_linp[1]; /* beginning of line pointer array */ } PageHeaderData; typedef PageHeaderData *PageHeader; @@ -160,8 +157,8 @@ typedef enum * returns true iff no itemid has been allocated on the page */ #define PageIsEmpty(page) \ - (((PageHeader) (page))->pd_lower == \ - (sizeof(PageHeaderData) - sizeof(ItemIdData)) ? true : false) + (((PageHeader) (page))->pd_lower <= \ + (sizeof(PageHeaderData) - sizeof(ItemIdData))) /* * PageIsNew @@ -175,7 +172,7 @@ typedef enum * Returns an item identifier of a page. */ #define PageGetItemId(page, offsetNumber) \ - ((ItemId) (&((PageHeader) (page))->pd_linp[(-1) + (offsetNumber)])) + ((ItemId) (&((PageHeader) (page))->pd_linp[(offsetNumber) - 1])) /* ---------------- * macros to access opaque space @@ -210,7 +207,7 @@ typedef enum * Sets the page size of a page. */ #define PageSetPageSize(page, size) \ - ((PageHeader) (page))->pd_opaque.od_pagesize = (size) + (((PageHeader) (page))->pd_opaque.od_pagesize = (size)) /* ---------------- * page special data macros @@ -244,7 +241,7 @@ typedef enum * Retrieves an item on the given page. * * Note: - * This does change the status of any of the resources passed. + * This does not change the status of any of the resources passed. * The semantics may change in the future. */ #define PageGetItem(page, itemId) \ @@ -264,7 +261,7 @@ typedef enum * The buffer can be a raw disk block and need not contain a valid * (formatted) disk page. */ -/* XXX dig out of buffer descriptor */ +/* XXX should dig out of buffer descriptor */ #define BufferGetPageSize(buffer) \ ( \ AssertMacro(BufferIsValid(buffer)), \ @@ -280,17 +277,17 @@ typedef enum /* * 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: The offset is invalid if the page is non-empty. - * Test whether PageIsEmpty before calling this routine - * and/or using its return value. + * NOTE: to ensure sane behavior if the page is not initialized + * (pd_lower == 0), cast the unsigned values to int before dividing. + * That way we get -1 or so, not a huge positive number... */ #define PageGetMaxOffsetNumber(page) \ -( \ - (((PageHeader) (page))->pd_lower - \ - (sizeof(PageHeaderData) - sizeof(ItemIdData))) \ - / sizeof(ItemIdData) \ -) + (((int) (((PageHeader) (page))->pd_lower - \ + (sizeof(PageHeaderData) - sizeof(ItemIdData)))) \ + / ((int) sizeof(ItemIdData))) /* ---------------------------------------------------------------- -- 2.40.0