This is expected behavior, not a bug. It'd be great to detect these
kinds of data corruption, but data checksums can't do that (and we don't
have other protections).
regards
On 8/6/26 16:11, Bram van der Vos wrote:
> *ISSUE*
>
> External modified datafile not detected, no error given but result produced;
>
> *REPRODUCTION*
>
> script.sh
> ---
>
> psql <<DO_CLEAN_1
> drop database corruption;
> DO_CLEAN_1
>
> rm -rf /tmp/oscmd.sh
> rm rf /tmp/output_1.txt
> rm rf /tmp/output_2.txt
>
> psql <<END_SCRIPT
>
> \o '/tmp/output_1.txt'
> select version();
> create database corruption;
> \c corruption
> show data_checksums;
> show ignore_checksum_failure;
> create table demo ( a serial, t timestamp with time zone);
> insert into demo (t) values (now());
> select max(t) from demo;
> select pg_relation_filepath('demo');
> copy (select command || setting ||'/'||file
> from (select * from (select 1 as my_order, 'rm -rf ' as command,
> pg_relation_filepath('demo') as file
> union all
> select 2 as my_order , 'touch ' as command ,
> pg_relation_filepath('demo') as file )
> cross join (select setting from pg_settings where
> name='data_directory')) order by my_order) to '/tmp/oscmd.sh';
> END_SCRIPT
>
>
> cat /tmp/output_1.txt
> chmod 700 /tmp/oscmd.sh
> /tmp/oscmd.sh
>
> psql -d corruption <<END_SCRIPT_2
>
> \o '/tmp/output_2.txt'
> select max(t) from demo;
> END_SCRIPT_2
>
> cat /tmp/output_2.txt
> ---
>
> *ETC*
> Result in tmp/output_1.txt en tmp/output_2.txt. After file has been
> removed and recreated with touch a NULL result is returned. The same
> happens when the has been replaced with dd -if /dev/zero of=<file>
> bs=1024 count=64000
>
> When replacing file with bogus data (/dev/random) an error is being
> returned. Result when the datafile is being nullified
>
> side info: pg_backrest does recognise the file as not valid an replaces
> is during restore
>
>
> regards
>
>
> Bram
>
> --
> vrijdags afwezig
> LOGO <https://www.axisintoict.nl>
> Bram van der Vos
> bram.van.der.vos@axisinto.nl
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>
--
Tomas Vondra
