Re: Deleting a table file does not raise an error when the table is touched afterwards, why?

On 30.05.2016 18:35, Daniel Westermann wrote:
> Hi,
>
> I need to understand something: Lets assume I have a table t5 with
> 1'000'000 rows:
>
> (postgres(at)[local]:5432) [sample] > select count(*) from t5;
> count
> ---------
> 1000000
> (1 row)
>
> Time: 2363.834 ms
> (postgres(at)[local]:5432) [sample] >
>
> I get the file for that table:
>
> postgres(at)pg_essentials_p1:/u02/pgdata/PG1/base/16422/ [PG1] oid2name
> -d sample -t t5
> From database "sample":
> Filenode Table Name
> ----------------------
> 32809 t5
>
>
> Then I delete the file:
>
> postgres(at)pg_essentials_p1:/u02/pgdata/PG1/base/16422/ [PG1] rm 32809
>
> When doing the count(*) on the table again:
>
> (postgres(at)[local]:5432) [sample] > select count(*) from t5;
> count
> ---------
> 1000000
> (1 row)
>
> No issue in the log. This is probably coming from the cache, isn't it?
> Is this intended and safe?
>
> Then I restart the instance and do the select again:
>
> 2016-05-30 19:25:20.633 CEST - 9 - 2777 - - @ FATAL: could not open
> file "base/16422/32809": No such file or directory
> 2016-05-30 19:25:20.633 CEST - 10 - 2777 - - @ CONTEXT: writing
> block 8192 of relation base/16422/32809
>
> (postgres(at)[local]:5432) [sample] > select count(*) from t5;
> count
> --------
> 437920
> (1 row)
>
> Can someone please tell me the intention behind that? From my point of
> view this is dangerous. If nobody is monitoring the log (which sadly
> is the case in reality) nobody will notice that only parts of the
> table are there. Wouldn't it be much more safe to raise an error as
> soon as the table is touched?
>
> PostgreSQL version:
>
> (postgres(at)[local]:5432) [sample] > select version();
> -[ RECORD 1
> ]----------------------------------------------------------------------------------------------------------------------------
> version | PostgreSQL 9.4.4 on x86_64-unknown-linux-gnu, compiled by
> gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4), 64-bit
>
> Thanks in advance
> Daniel
>

Hi if you delete file from external process that open this file this
external process never ever notice it. Only after it close this file
handler you fall it some issues with "file not exist" and other.

Alex Ignatov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company