Re: Unlogged Crash Detection

On Tue, Aug 29, 2017 at 6:06 PM, Gersner <gersner(at)gmail(dot)com> wrote:
> I see, interesting.

Please do not top-post. This is not the recommended way of dealing
with threads on this mailing list.

> We have lots of unlogged tables, upon a crash we want to create a
> feedback/alert that data disappeared.
>
> Not very familiar with the internal structure, but is it possible to
> identify if the current table is the INIT_FORKNUM?

Using pg_relation_filepath, you can know the path to a relation file
on disk. So a simple idea would be to use pg_read_binary_file with the
path of the file and the path of the init fork, which is suffixed with
"_init", and then a comparison between both. If the data read is the
same, the relation has been untouched. Note that you can only do such
a thing as a superuser, and that the data is read from disk, not from
shared buffers. So that's not perfect, but it give an indication.
--
Michael