From: | Ben Chobot <bench(at)silentmedia(dot)com> |
---|---|
To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, pgsql-general <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: 12.3 replicas falling over during WAL redo |
Date: | 2020-08-03 22:10:49 |
Message-ID: | 8cb30a3b-72a6-512a-7ce4-dce671c76379@silentmedia.com |
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Lists: | pgsql-general |
Peter Geoghegan wrote on 8/3/20 3:04 PM:
> On Mon, Aug 3, 2020 at 2:35 PM Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
>> 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
> Ben might find this approach to dumping out a single page image
> easier, since it doesn't involve relfilenodes or filesystem files:
>
> https://wiki.postgresql.org/wiki/Getting_a_stack_trace_of_a_running_PostgreSQL_backend_on_Linux/BSD#contrib.2Fpageinspect_page_dump
I don't think that works, because it sounds like this requires I connect
to the db, but that means I have to start it up. I am (wrongly?)
assuming we should get what we can while the db is still in a
just-crashed state.
Still, I seem to have mangled Alvaro's suggestion somehow, because this
doesn't look right:
# select h.* from public.page , page_header(raw) h;
lsn | checksum | flags | lower | upper | special | pagesize | version
| prune_xid
-----+----------+-------+-------+-------+---------+----------+---------+-----------
0/0 | 0 | 0 | 0 | 0 | 0 | 0 | 0
| 0
(1 row)
I'll keep trying though.
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