On 2020-Aug-03, Ben Chobot wrote:
> Alvaro Herrera wrote on 8/3/20 12:34 PM:
> > On 2020-Aug-03, Ben Chobot wrote:
> >
> > Yep. Looking at the ones in block 6501,
> >
> > > rmgr: Btree len (rec/tot): 72/ 72, tx: 76393394, lsn:
> > > A0A/AB2C43D0, prev A0A/AB2C4378, desc: INSERT_LEAF off 41, blkref #0: rel
> > > 16605/16613/60529051 blk 6501
> > > rmgr: Btree len (rec/tot): 72/ 72, tx: 76396065, lsn:
> > > A0A/AC4204A0, prev A0A/AC420450, desc: INSERT_LEAF off 48, blkref #0: rel
> > > 16605/16613/60529051 blk 6501
> > My question was whether the block has received the update that added the
> > item in offset 41; that is, is the LSN in the crashed copy of the page
> > equal to A0A/AB2C43D0? If it's an older value, then the write above was
> > lost for some reason.
>
> How do I tell?
You can use pageinspect's page_header() function to obtain the page's
LSN. You can use dd to obtain the page from the file,
dd if=16605/16613/60529051 bs=8192 count=1 seek=6501 of=/tmp/page.6501
then put that binary file in a bytea column, perhaps like
create table page (raw bytea);
insert into page select pg_read_binary_file('/tmp/page');
and with that you can run page_header:
create extension pageinspect;
select h.* from page, page_header(raw) h;
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services