Converted to page.sgml. Not needed in a man page.

src/man/page.5

-.\" This is -*-nroff-*-
-.\" XXX standard disclaimer belongs here....
-.\" $Header: /cvsroot/pgsql/src/man/Attic/page.5,v 1.3 1998/01/11 22:17:46 momjian Exp $
-.TH PAGE FILES 01/23/93 PostgreSQL PostgreSQL
-.SH NAME
-page structure - Postgres database file default page format
-.SH DESCRIPTION
-This section provides an overview of the page format used by Postgres
-classes.  User-defined access methods need not use this page format.
-.PP
-In the following explanation, a
-.BR byte
-is assumed to contain 8 bits.  In addition, the term
-.BR item
-refers to data which is stored in Postgres classes.
-.if t \{
-Diagram 1 shows how pages in both normal Postgres classes and Postgres index
-classes (e.g., a B-tree index) are structured.
-.\" This is -*-nroff-*-
-.\" XXX standard disclaimer belongs here....
-.\" $Header: /cvsroot/pgsql/src/man/Attic/page.5,v 1.3 1998/01/11 22:17:46 momjian Exp $
-.in +0.5i
-.(b M
-.PS
-.ps 11
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-line from 0.988,9.012 to 6.487,9.012
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-"\s10\fRitemPointerData\fP" at 2.925,7.978 ljust
-"\s10\fRfiller\fP" at 4.562,7.978 ljust
-"\s10\fRitemData...\fP" at 5.513,7.978 ljust
-"\s10\fIUnallocated Space\fP" at 3.237,8.753 ljust
-"\s10\fBItemContinuationData\fP" at 3.663,8.415 ljust
-"\s10\fISpecial Space\fP" at 4.688,6.240 ljust
-"\s10\fI``ItemData 2''\fP" at 2.587,7.478 ljust
-"\s10\fI``ItemData 1''\fP" at 3.413,6.865 ljust
-"\s10\fBItemIdData\fP" at 4.775,9.715 ljust
-"\s10\fBPageHeaderData\fP" at 1.875,9.715 ljust
-.PE
-.ce 
-.BR "Diagram 1: Sample Page Layout"
-.)b
-.in -0.5i
-\}
-.\" Running
-.\" .q .../bin/dumpbpages
-.\" or
-.\" .q .../src/support/dumpbpages
-.\" as the postgres superuser
-.\" with the file paths associated with
-.\" (heap or B-tree index) classes,
-.\" .q .../data/base/<database-name>/<class-name>,
-.\" will display the page structure used by the classes.
-.\" Specifying the
-.\" .q -r
-.\" flag will cause the classes to be
-.\" treated as heap classes and for more information to be displayed.
-.PP
-The first 8 bytes of each page consists of a page header
-.RB ( PageHeaderData ).
-Within the header, the first three 2-byte integer fields,
-.IR lower ,
-.IR upper ,
-and
-.IR special ,
-represent byte offsets to the start of unallocated space, to the end
-of unallocated space, and to the start of \*(lqspecial space.\*(rq
-Special space is a region at the end of the page which is allocated at
-page initialization time and which contains information specific to an
-access method.  The last 2 bytes of the page header,
-.IR opaque ,
-encode the page size and information on the internal fragmentation of
-the page.  Page size is stored in each page because frames in the
-buffer pool may be subdivided into equal sized pages on a frame by
-frame basis within a class.  The internal fragmentation information is
-used to aid in determining when page reorganization should occur.
-.PP
-Following the page header are item identifiers
-.RB ( ItemIdData ).
-New item identifiers are allocated from the first four bytes of
-unallocated space.  Because an item identifier is never moved until it
-is freed, its index may be used to indicate the location of an item on
-a page.  In fact, every pointer to an item
-.RB ( ItemPointer )
-created by Postgres consists of a frame number and an index of an item
-identifier.  An item identifier contains a byte-offset to the start of
-an item, its length in bytes, and a set of attribute bits which affect
-its interpretation.
-.PP
-The items, themselves, are stored in space allocated backwards from
-the end of unallocated space.  Usually, the items are not interpreted.
-However when the item is too long to be placed on a single page or
-when fragmentation of the item is desired, the item is divided and
-each piece is handled as distinct items in the following manner.  The
-first through the next to last piece are placed in an item
-continuation structure
-.BR ( ItemContinuationData ).
-This structure contains
-.IR itemPointerData
-which points to the next piece and the piece itself.  The last piece
-is handled normally.
-.SH FILES
-.TP 5n
-\&.../data/...
-Location of shared (global) database files.
-.TP 5n
-\&.../data/base/... 
-Location of local database files.
-.SH BUGS
-The page format may change in the future to provide more efficient
-access to large objects.
-.PP
-This section contains insufficient detail to be of any assistance in
-writing a new access method.