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| author | Peter Eisentraut <peter_e@gmx.net> | 2017-03-17 09:49:10 -0400 |
|---|---|---|
| committer | Peter Eisentraut <peter_e@gmx.net> | 2017-03-17 10:55:17 -0400 |
| commit | fef2bcdcba0888c95ddf2a7535179c3b9a6a2f0e (patch) | |
| tree | f0234ec4b3b6ac47d293254b9043d2f62b462aca /doc/src | |
| parent | 64ae420b275a82534732aafd9d550b9982ca0a5d (diff) | |
pageinspect: Add page_checksum function
Author: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Reviewed-by: Ashutosh Sharma <ashu.coek88@gmail.com>
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/pageinspect.sgml | 47 |
1 files changed, 45 insertions, 2 deletions
diff --git a/doc/src/sgml/pageinspect.sgml b/doc/src/sgml/pageinspect.sgml index 5e6712f9cde..9f41bb21eb9 100644 --- a/doc/src/sgml/pageinspect.sgml +++ b/doc/src/sgml/pageinspect.sgml @@ -73,12 +73,55 @@ test=# SELECT * FROM page_header(get_raw_page('pg_class', 0)); lsn | checksum | flags | lower | upper | special | pagesize | version | prune_xid -----------+----------+--------+-------+-------+---------+----------+---------+----------- - 0/24A1B50 | 1 | 1 | 232 | 368 | 8192 | 8192 | 4 | 0 + 0/24A1B50 | 0 | 1 | 232 | 368 | 8192 | 8192 | 4 | 0 </screen> The returned columns correspond to the fields in the <structname>PageHeaderData</> struct. See <filename>src/include/storage/bufpage.h</> for details. - </para> + </para> + + <para> + The <structfield>checksum</structfield> field is the checksum stored in + the page, which might be incorrect if the page is somehow corrupted. If + data checksums are not enabled for this instance, then the value stored + is meaningless. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>page_checksum(page bytea, blkno int4) returns smallint</function> + <indexterm> + <primary>page_checksum</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>page_checksum</function> computes the checksum for the page, as if + it was located at the given block. + </para> + + <para> + A page image obtained with <function>get_raw_page</function> should be + passed as argument. For example: +<screen> +test=# SELECT page_checksum(get_raw_page('pg_class', 0), 0); + page_checksum +--------------- + 13443 +</screen> + Note that the checksum depends on the block number, so matching block + numbers should be passed (except when doing esoteric debugging). + </para> + + <para> + The checksum computed with this function can be compared with + the <structfield>checksum</structfield> result field of the + function <function>page_header</function>. If data checksums are + enabled for this instance, then the two values should be equal. + </para> </listitem> </varlistentry> |