On Thu, Sep 10, 2015 at 12:42 AM, Fujii Masao <[email protected]> wrote:
> On Tue, Jul 21, 2015 at 9:59 AM, Michael Paquier
> <[email protected]> wrote:
>> On Tue, Jul 21, 2015 at 6:54 AM, Vignesh Raghunathan
>> <[email protected]> wrote:
>>> Hello,
>>>
>>> It has been mentioned in Section 63.6 that the first two fields in
>>> PageHeaderData track the most recent WAL entry related to the page. However,
>>> I am not sure how pd_checksum is related to WAL. Could it be possible that
>>> the sentence has been carried over from previous versions of the
>>> documentations without considering the change to the second field in
>>> PageHeaderData?
>>
>> Yes, the documentation is mistaken. The two bytes of pd_tli have been
>> switched to pd_checksum in 9.3, hence only the first field is relevant
>> for WAL, aka pd_lsn. Looking at this portion of the docs I think that
>> it should be updated as attached, mentioning pd_checksum as well.
>
> Also the type of pd_lsn in the Table 63-3 should be PageXLogRecPtr.
Yep. See attached FWIW.
--
Michael
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml
index e5b7b4b..0153b08 100644
--- a/doc/src/sgml/storage.sgml
+++ b/doc/src/sgml/storage.sgml
@@ -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>
--
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