Re: Online checksums patch - once again - Mailing list pgsql-hackers

> On 5 Jan 2021, at 18:19, Michael Banck <michael.banck@credativ.de> wrote:

>> diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
>> index 385ac25150..e3b0048806 100644
>> --- a/doc/src/sgml/ref/initdb.sgml
>> +++ b/doc/src/sgml/ref/initdb.sgml
>> @@ -219,6 +219,7 @@ PostgreSQL documentation
>>         failures will be reported in the
>>         <link linkend="monitoring-pg-stat-database-view">
>>         <structname>pg_stat_database</structname></link> view.
>> +        See <xref linkend="checksums" /> for details.
>>        </para>
>>       </listitem>
>>      </varlistentry>
>
>> diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
>> index f4bc147b10..5dcfcdd2ff 100644
>> --- a/doc/src/sgml/wal.sgml
>> +++ b/doc/src/sgml/wal.sgml
>> @@ -230,6 +230,103 @@
>>   </para>
>>  </sect1>
>>
>> + <sect1 id="checksums">
>> +  <title>Data Checksums</title>
>> +  <indexterm>
>> +   <primary>checksums</primary>
>> +  </indexterm>
>> +
>> +  <para>
>> +   Data pages are not checksum protected by default, but this can optionally be
>> +   enabled for a cluster.  When enabled, each data page will be assigned a
>> +   checksum that is updated when the page is written and verified every time
>> +   the page is read. Only data pages are protected by checksums, internal data
>> +   structures and temporary files are not.
>> +  </para>
>> +
>> +  <para>
>> +   Checksums are normally enabled when the cluster is initialized using <link
>> +   linkend="app-initdb-data-checksums"><application>initdb</application></link>.
>> +   They can also be enabled or disabled at a later time, either as an offline
>> +   operation or in a running cluster. In all cases, checksums are enabled or
>> +   disabled at the full cluster level, and cannot be specified individually for
>> +   databases or tables.
>> +  </para>
>> +
>> +  <para>
>> +   The current state of checksums in the cluster can be verified by viewing the
>> +   value of the read-only configuration variable <xref
>> +   linkend="guc-data-checksums" /> by issuing the command <command>SHOW
>> +   data_checksums</command>.
>> +  </para>
>> +
>> +  <para>
>> +   When attempting to recover from corrupt data it may be necessary to bypass
>> +   the checksum protection in order to recover data. To do this, temporarily
>> +   set the configuration parameter <xref linkend="guc-ignore-checksum-failure" />.
>> +  </para>
>
> I think the above is rather informative about checksums in general and
> not specific to online activation of checksusm, so could pretty much be
> committed verbatim right now, except for the "either as an offline
> operation or in a running cluster" bit which would have to be rewritten.

That might indeedbe useful regardless of the state of this patch.  Robert and
Heikki: being committers who have both reviewed recent versions of the patch,
would you prefer these sections be broken out into a separate patch?

cheers ./daniel