Re: hunt for 2.6.37 dm-crypt+ext4 corruption? (was: Re: dm-crypt barrier support is effective)

["Ted Ts'o" <tytso@mit.edu>]

On Tue, Dec 07, 2010 at 01:22:43PM -0500, Mike Snitzer wrote:
> > 1. create a database (from bash):
> > 
> > createdb test
> > 
> > 2. place the following contents in a file (I used 't.sql'):
> > 
> > begin;
> > create temporary table foo as select x as a, ARRAY[x] as b FROM
> > generate_series(1, 10000000 ) AS x;
> > create index foo_a_idx on foo (a);
> > create index foo_b_idx on foo USING GIN (b);
> > rollback;
> > 
> > 3. execute that sql:
> > 
> > psql -f t.sql --echo-all test
> > 
> > With 2.6.34.7 I can re-run [3] all day long, as many times as I want,
> > without issue.
> > 
> > With 2.6.37-rc4-13 (the currently-installed KOTD kernel) if tails
> > pretty frequently.

So I just tried to reproduce this on an Ubuntu 10.04 system running
2.6.37-rc5 (completely stock except for a few apparmor patches that I
needed to keep the apparmor userspace from complaining).  I'm using
Postgres 8.4.5-0ubuntu10.04.

Using the above procedure, I wasn't able to reproduce.  Then I
realized this might have been because I was using an SSD root file
system (which is secured using LUKS/dm-crypt, with LVM on top of
dm-crypt).  So I mounted a file system on a 5400 rpm SSD disk, which
is also protected using LUKS/dm-crypt with LVM on top.  I then
executed the PostgresQL commands:

CREATE TABLESPACE test LOCATION '/kbuild/postgres';
SET default_tablespace = test;
COMMIT
\quit

I then re-ran the above proceduing, and verified that all of the I/O
was going to the 5400rpm laptop disk.

I then ran the above procedure a half-dozen times, and I still haven't
been able to reproduce any Postgresql errors or kernel errors.

Jon, can you help me identify what might be different with your run
and mine?  What version of Postgres are you using?

Thanks,

						- Ted