Invalid page header

**Ed L.** · Nov 23 '05, 02:36 AM

Re: Invalid page header

On Wednesday October 20 2004 5:34, Ed L. wrote:[color=blue]
> I have 5 corrupted page headers as evidenced by these errors:
>
> ERROR: Invalid page header in block 13947 of ...
>
> The corruption is causing numerous queries to abort. First option is to
> try to salvage data before attempt restore from backup. I want to try to
> edit the file to zero out the bogus headers. I realize there may be data
> lost from this attempt. I have scalpel (binary editor) in hand.
>
> Which bytes should I edit, and what do I make them?[/color]

In other words, how do I calculate which bytes to zero to simulate
zero_damaged_pa ges??

TIA.

[color=blue]
>
>
> $ pg_filedump -if -R 1343 1343 25268878.386509 46
>
> *************** *************** *************** *************** *****
> * PostgreSQL File/Block Formatted Dump Utility - Version 1.1
> *
> * File: 25268878.386509 46
> * Options used: -if -R 1343 1343
> *
> * Dump created on: Wed Oct 20 19:14:06 2004
> *************** *************** *************** *************** *****
>
> Block 1343 *************** *************** *************** *********
> <Header> -----
> Block Offset: 0x00a7e000 Offsets: Lower 0 (0x0000)
> Block: Size 0 Version 0 Upper 0 (0x0000)
> LSN: logid 0 recoff 0x00000000 Special 0 (0x0000)
> Items: -5 Free Space: 0
> Length (including item array): 24
>
> Error: Invalid header information.
>
> 0000: 00000000 00000000 00000000 00000000 ............... .
> 0010: 00000000 00000000 ........
>
> <Data> ------
> Error: Item index corrupt on block. Offset: <-5>.
>
> <Special Section> -----
> Error: Invalid special section encountered.
> Error: Special section points off page. Unable to dump contents.
>
> *** End of Requested Range Encountered. Last Block Read: 1343 ***[/color]

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**Ed L.** · Nov 23 '05, 02:36 AM

Re: Invalid page header

On Wednesday October 20 2004 10:12, Ed L. wrote:[color=blue]
> On Wednesday October 20 2004 10:00, Tom Lane wrote:[color=green]
> > "Ed L." <pgsql@bluepolk a.net> writes:[color=darkred]
> > > In other words, how do I calculate which bytes to zero to simulate
> > > zero_damaged_pa ges??[/color]
> >
> > Why simulate it, when you can just turn it on? But anyway, the answer
> > is "the whole page".[/color]
>
> Old 7.3.4 installation, didn't realize that feature was there. Thx.[/color]

That worked for 3 of 4 cases, but for a fourth, I see the message that it's
zeroing the page, but then it continues to report invalid page header for
that block... maybe the header is too fouled up to fix?

Ed

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**Tom Lane** · Nov 23 '05, 02:36 AM

Re: Invalid page header

"Ed L." <pgsql@bluepolk a.net> writes:[color=blue]
> In other words, how do I calculate which bytes to zero to simulate
> zero_damaged_pa ges??[/color]

Why simulate it, when you can just turn it on? But anyway, the answer
is "the whole page".

regards, tom lane

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**Ed L.** · Nov 23 '05, 02:36 AM

Re: Invalid page header

On Wednesday October 20 2004 10:00, Tom Lane wrote:[color=blue]
> "Ed L." <pgsql@bluepolk a.net> writes:[color=green]
> > In other words, how do I calculate which bytes to zero to simulate
> > zero_damaged_pa ges??[/color]
>
> Why simulate it, when you can just turn it on? But anyway, the answer
> is "the whole page".[/color]

Old 7.3.4 installation, didn't realize that feature was there. Thx.

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**Ed L.** · Nov 23 '05, 02:36 AM

Re: Invalid page header

On Wednesday October 20 2004 10:43, Ed L. wrote:[color=blue]
> On Wednesday October 20 2004 10:12, Ed L. wrote:[color=green]
> > On Wednesday October 20 2004 10:00, Tom Lane wrote:[color=darkred]
> > > "Ed L." <pgsql@bluepolk a.net> writes:
> > > > In other words, how do I calculate which bytes to zero to simulate
> > > > zero_damaged_pa ges??
> > >
> > > Why simulate it, when you can just turn it on? But anyway, the
> > > answer is "the whole page".[/color]
> >
> > Old 7.3.4 installation, didn't realize that feature was there. Thx.[/color]
>
> That worked for 3 of 4 cases, but for a fourth, I see the message that
> it's zeroing the page, but then it continues to report invalid page
> header for that block... maybe the header is too fouled up to fix?[/color]

I didn't notice zero_damaged_pa ges because it doesn't show up by default in
the postgresql.conf file, I guess wisely since it is somewhat dangerous to
the forensic evidence.

I fixed the case that zero_damaged_pa ges didn't by truncating the file at
the precise byte offset reported by pg_filedump for the bad block via
'pg_filedump -if -R ...'

Ed

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