Fwd: ERROR invalid page header in block xxx of relation base/xxxxx/xxxxx/

Forgot to loop community

Hi Jorge/All,
Thanks for the reply.
As per the documentation , I think backend reads the this page header and
reports that it is damaged.
I am looking at ways we re-create this scenario of creation this blank
corrupted page ? do I have any control over Backend and after it
initializes a new page using function PageInit
<https://doxygen.postgresql.org/bufpage_8c.html#ab871202326b101c6ec24b7f628157c2c>
(Page
<https://doxygen.postgresql.org/bufpage_8h.html#a2010e3258a7075b32ad5750134ab9c5c>
page, Size
<https://doxygen.postgresql.org/c_8h.html#af9ecec2d692138fab9167164a457cbd4>
pageSize, Size
<https://doxygen.postgresql.org/c_8h.html#af9ecec2d692138fab9167164a457cbd4>
specialSize) and I want to halt/crash the backend by stopping postgres
database or through Hardware/system crash ?
Is this possible ?

Also I see that based on below comments from Source code, having such pages
in database is normal . is my understanding correct ?

/*
63 * PageIsVerified
64 * Check that the page header and checksum (if any) appear valid.
65 *
66 * This is called when a page has just been read in from disk. The idea
is
67 * to cheaply detect trashed pages before we go nuts following bogus item
68 * pointers, testing invalid transaction identifiers, etc.
69 *
70 * It turns out to be necessary to allow zeroed pages here too. Even
though
71 * this routine is *not* called when deliberately adding a page to a
relation,
72 * there are scenarios in which a zeroed page might be found in a table.
73 * (Example: a backend extends a relation, then crashes before it can
write
74 * any WAL entry about the new page. The kernel will already have the
75 * zeroed page in the file, and it will stay that way after restart.) So
we
76 * allow zeroed pages here, and are careful that the page access macros
77 * treat such a page as empty and without free space. Eventually, VACUUM
78 * will clean up such a page and make it usable.
79 */
zero_damaged_pages (boolean)

Detection of a damaged page header normally causes PostgreSQL to report an
error, aborting the current transaction. Setting zero_damaged_pages to on
causes the system to instead report a warning, zero out the damaged page in
memory, and continue processing. This behavior will destroy data, namely
all the rows on the damaged page. However, it does allow you to get past
the error and retrieve rows from any undamaged pages that might be present
in the table. It is useful for recovering data if corruption has occurred
due to a hardware or software error. You should generally not set this on
until you have given up hope of recovering data from the damaged pages of a
table. Zeroed-out pages are not forced to disk so it is recommended to
recreate the table or the index before turning this parameter off again.
The default setting is off, and it can only be changed by a superuser.

On Thu, Dec 8, 2016 at 9:50 AM, Jorge Torralba <jorge(dot)torralba(at)gmail(dot)com>
wrote:

> Look into this setting.
>
> zero_damaged_pages = on;
>
> The docs should explain it.
>
>
>
> On Wed, Dec 7, 2016 at 2:47 PM, sreekanth Palluru <sree4pg(at)gmail(dot)com>
> wrote:
>
>> Hi ,
>>
>> I am getting invalid page header error and what I could observe is when I
>> select the table I get this error , where as if I select table and order by
>> primary key I can retrieve the rows from table.
>>
>> And I don't see any dataloss ( based on total number records) after
>> fixing the blocks using zero_damaged_pages=on and then vacuum full on the
>> table
>>
>>
>> Please note I have renamed few tables to avoid giving actual table names
>>
>> We run Postgres 9.2 version on Windows and Dell Optiplex XE2 server and
>> we suspect that block corruption would have happen due to
>> hardware/memory/power failures reasons and I have gone through wikik
>> https://wiki.postgresql.org/wiki/Reliable_Writes.
>>
>> I want to understand why we can read the table through where there exists
>> index and explain plan shows Index scan and with high cost compare to seq
>> scan .
>> I assume that since there no rows/data present in these corrupted blocks
>> index scan skips these blocks and hence it is not throwing the error .
>>
>> Also , I want to know what would have caused the postgres to create these
>> corrupted blocks and
>> can I reproduce this error ? appreciate if you share any pointers to
>> blogs/mailing lists if this type of issue is already discussed ?
>>
>>
>> create table a.parametertable_bak as select * from a.parametertable order
>> by id;
>>
>> labs=# select count(*) from a.parametertable_bak ;
>> count
>> -------
>> 31415
>> (1 row)
>>
>>
>> labs=#
>> labs=# checkpoint;
>> CHECKPOINT
>> labs=# set zero_damaged_pages=on;
>> SET
>> labs=# vacuum full a.parametertable;
>> WARNING: invalid page header in block 204 of relation base/16413/16900;
>> zeroing out page
>> WARNING: invalid page header in block 205 of relation base/16413/16900;
>> zeroing out page
>> VACUUM
>> labs=# select count(*) from a.parametertable ;
>> count
>> -------
>> 31415
>> (1 row)
>>
>>
>> labs=#
>> -Sreekanth
>>
>
>
>
> --
> Thanks,
>
> Jorge Torralba
> ----------------------------
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--
Regards
Sreekanth

--
Regards
Sreekanth