<para>

The first 24 bytes of each page consists of a page header

(PageHeaderData). Its format is detailed in <xref

linkend="pageheaderdata-table">. The firsttwo fields track the most

recent WAL entry related to this page.Next is a 2-bytefield

and<structfield>pd_special</structfield>). These contain byte offsets

thespecialspace.

The next 2 bytesof thepage 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 firstfield tracks the most

recent WAL entry related to this page.The secondfield contains

by three 2-byte integer fields (<structfield>pd_lower</structfield>,

fromthepage start to the start of unallocatedspace, to the end of

unallocated space, and to the startof thespecial space. The next 2

bytes of the page header,<structfield>pd_pagesize_version</structfield>,

store both the page sizeand 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;

<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>