DIRECTORYDBEnvironment USING[InternalError];DBStoragePagetags: CEDAR DEFINITIONSIMPORTS DBEnvironment = BEGINPageHeader: TYPE = MACHINE DEPENDENT RECORD[pageTag: CARDINAL [0..256),dontCare: CARDINAL [0..256)];  -- PageHeaderUnused: CARDINAL = 0;         -- unused page, obtained by extending Juniper fileFree: CARDINAL = 1;           -- page on segment or local free listAMap: CARDINAL = 2;           -- page used to store segment address-map valuesTuple: CARDINAL = 3;          -- page used to store tuplesSystemTuple: CARDINAL = 4;    -- page used to store system tuplesOverflowTuple: CARDINAL = 5;  -- page used to store overflow tuples & long stringsBTree: CARDINAL = 6;          -- page used to store part of a B-treeAssertPageIsTuplePage: PROC[p: LONG POINTER] = TRUSTED INLINE {SELECT LOOPHOLE[p,LONG POINTER TO PageHeader].pageTag FROMTuple => {};ENDCASE => ERROR DBEnvironment.InternalError; -- BadPageTag};  -- AssertPageIsTuplePageAssertPageIsSystemTuplePage: PROC[p: LONG POINTER] = TRUSTED INLINE {SELECT LOOPHOLE[p,LONG POINTER TO PageHeader].pageTag FROMSystemTuple => {};ENDCASE => ERROR DBEnvironment.InternalError; -- BadPageTag};  -- AssertPageIsSystemTuplePageAssertPageIsAnyTuplePage: PROC[p: LONG POINTER] = TRUSTED INLINE { SELECT LOOPHOLE[p,LONG POINTER TO PageHeader].pageTag FROMTuple, SystemTuple => {};ENDCASE => ERROR DBEnvironment.InternalError; -- BadPageTag};  -- AssertPageIsAnyTuplePageAssertPageIsOverflowTuplePage: PROC[p: LONG POINTER] = TRUSTED INLINE {SELECT LOOPHOLE[p,LONG POINTER TO PageHeader].pageTag FROMOverflowTuple => {};ENDCASE => ERROR DBEnvironment.InternalError; -- BadPageTag};  -- AssertPageIsOverflowTuplePageEND.  -- DBStoragePagetagsCreated by MBrown on February 15, 1980  11:08 AMChanged by MBrown on July 9, 1980  9:50 PMChanged by MBrown on August 13, 1980  4:51 PMChanged by MBrown on September 26, 1980  11:29 AMChanged by Willie-Sue on February 14, 1985  X  File: DBStoragePagetags.mesaCopyright c 1985 by Xerox Corporation.  All rights reserved.Last edited by:MBrown on September 26, 1980  11:30 AMCattell on January 14, 1983 2:04 pmWillie-Sue, February 15, 1985 11:09:19 am PSTThis interface defines the values of the page tags found on all pages in the system.  Onepurpose of having a uniform page tag convention is to aid the scavenger.  The page tag is storedin the first byte of each page.  The other byte of the first word is uncommitted.  The PageHeaderdeclaration below is included for purposes of illustration:First word of a page.Page tag values.in future: HashTable, BitVector, etc...Module HistoryAdded AssertPageIsTuplePage, AssertPageIsSystemTuplePage, AssertPageIsAnyTuplePage.Added AssertPageIsOverflowTuplePage.Change to new DBException.Made Cedar, added tioga formattingÊ  ˜ šœ™Jšœ
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