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Correct description of PageHeaderData layout in documentation

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Back-patch to 9.3 where PageHeaderData layout was changed.

Michael Paquier
This commit is contained in:
Fujii Masao 2015-09-11 13:02:15 +09:00
parent 103ef20211
commit a1b2888517
1 changed files with 13 additions and 13 deletions
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26
doc/src/sgml/storage.sgml
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@ -758,18 +758,18 @@ data. Empty in ordinary tables.</entry>
<para>
The first 24 bytes of each page consists of a page header
(PageHeaderData). Its format is detailed in <xref
linkend="pageheaderdata-table">. The first two fields track the most
recent WAL entry related to this page. Next is a 2-byte field
containing flag bits. This is followed by three 2-byte integer fields
(<structfield>pd_lower</structfield>, <structfield>pd_upper</structfield>,
and <structfield>pd_special</structfield>). These contain byte offsets
from the page start to the start
of unallocated space, to the end of unallocated space, and to the start of
the special space.
The next 2 bytes of the page header,
<structfield>pd_pagesize_version</structfield>, store both the page size
and a version indicator. Beginning with
(<structname>PageHeaderData</>). Its format is detailed in <xref
linkend="pageheaderdata-table">. The first field tracks the most
recent WAL entry related to this page. The second field contains
the page checksum if <xref linkend="app-initdb-data-checksums"> are
enabled. Next is a 2-byte field containing flag bits. This is followed
by three 2-byte integer fields (<structfield>pd_lower</structfield>,
<structfield>pd_upper</structfield>, and
<structfield>pd_special</structfield>). These contain byte offsets
from the page start to the start of unallocated space, to the end of
unallocated space, and to the start of the special space. The next 2
bytes of the page header, <structfield>pd_pagesize_version</structfield>,
store both the page size and a version indicator. Beginning with
<productname>PostgreSQL</productname> 8.3 the version number is 4;
<productname>PostgreSQL</productname> 8.1 and 8.2 used version number 3;
<productname>PostgreSQL</productname> 8.0 used version number 2;
@ -799,7 +799,7 @@ data. Empty in ordinary tables.</entry>
<tbody>
<row>
<entry>pd_lsn</entry>
<entry>XLogRecPtr</entry>
<entry>PageXLogRecPtr</entry>
<entry>8 bytes</entry>
<entry>LSN: next byte after last byte of xlog record for last change
to this page</entry>