diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/storage.sgml | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml index a66aeb2584e..93950dde297 100644 --- a/doc/src/sgml/storage.sgml +++ b/doc/src/sgml/storage.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/storage.sgml,v 1.18 2007/06/03 17:05:53 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/storage.sgml,v 1.19 2007/09/21 21:25:42 tgl Exp $ --> <chapter id="storage"> @@ -416,7 +416,7 @@ Item <row> <entry>PageHeaderData</entry> - <entry>20 bytes long. Contains general information about the page, including + <entry>24 bytes long. Contains general information about the page, including free space pointers.</entry> </row> @@ -449,7 +449,7 @@ data. Empty in ordinary tables.</entry> <para> - The first 20 bytes of each page consists of a page header + 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 @@ -459,7 +459,7 @@ data. Empty in ordinary tables.</entry> 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 last 2 bytes of the page header, + 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; @@ -471,6 +471,8 @@ data. Empty in ordinary tables.</entry> versions, but the layout of heap row headers has.) The page size is basically only present as a cross-check; there is no support for having more than one page size in an installation. + The last field is a hint that shows whether pruning the page is likely + to be profitable: it tracks the oldest un-pruned XMAX on the page. </para> @@ -530,6 +532,12 @@ data. Empty in ordinary tables.</entry> <entry>2 bytes</entry> <entry>Page size and layout version number information</entry> </row> + <row> + <entry>pd_prune_xid</entry> + <entry>TransactionId</entry> + <entry>4 bytes</entry> + <entry>Oldest unpruned XMAX on page, or zero if none</entry> + </row> </tbody> </tgroup> </table> |