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Re: svn commit: r1628093 - in /subversion/trunk/subversion/libsvn_fs_fs: index.c structure-indexes

From: Stefan Fuhrmann <stefan.fuhrmann_at_wandisco.com>
Date: Tue, 30 Sep 2014 11:44:04 +0200

On Tue, Sep 30, 2014 at 11:15 AM, Stefan Sperling <stsp_at_apache.org> wrote:

> On Mon, Sep 29, 2014 at 07:18:05PM +0200, Stefan Fuhrmann wrote:
> > On Sun, Sep 28, 2014 at 11:17 PM, Stefan Sperling <stsp_at_apache.org>
> wrote:
> >
> > > On Sun, Sep 28, 2014 at 05:56:01PM -0000, stefan2_at_apache.org wrote:
> > > > Author: stefan2
> > > > Date: Sun Sep 28 17:56:01 2014
> > > > New Revision: 1628093
> > > >
> > > > URL: http://svn.apache.org/r1628093
> > > > Log:
> > > > Support FSFS format 7 commits in load balanced mixed-architecture
> > > clusters.
> > > >
> > > > At least theoretically, machines with different endianess or off_t
> sizes
> > > > might access the same repository on e.g. an iSCSI SAN. Then the
> machine
> > > > performing a commit may have a different architecture from the one
> > > building
> > > > up the transaction. To allow that, even the intermediate (proto-)
> index
> > > > format within those transactions must be platform-independent.
> > >
> > > Hi Stefan,
> > >
> > > If you describe in some more detail how to set it up I can test this
> > > scenario for you on OpenBSD with sparc64 (64bit big-endian), amd64
> > > (64bit little endian), macppc (32bit big-endian) and i386 (32bit little
> > > endian) machines.
> > >
> >
> > Thanks for the offer. So, this is the issue that I addressed
> > with the above patch:
> >
> > At the FS API level, transactions can be opened (and implicitly
> > closed again) many times before being committed. If these
> > operations are performed from different machines accessing
> > the same repository, they might not agree upon C struct size,
> > layout or interpretation. So, for pure API consistency alone,
> > all data within a txn needs to be portable / architecture independent.
> >
> > I may be wrong but I vaguely remember that the HTTP client
> > sends the "commit" operation over a separate connection that
> > the one it used to build up the txn. If there is a load balancer
> > in front of the actual servers, that commit may get served by
> > a different machine.
> >
> > Testing the general scenario is simpler, though. Have one machine
> > build up a transaction which touches a few of nodes (such that
> > different record sizes would result in missing / misaligned data).
> > Then e.g. copy the repo to a different machine and let that one
> > do the commit. The result must then pass 'svnadmin verify'.
> >
> > The critical combinations are little / big endian and 32 bit vs.
> > 64 bit file offsets (not the same thing as 32 / 64 bit in general).
> > So, 64 bit big endian vs. 32 bit little endian with 32 bit off_t
> > would probably cover it. Tests with both machines in both
> > roles (txn creation and txn commit).
> >
> > -- Stefan^2.
>
> How do you open a transaction and postpone the commit?
> Using some custom code written against the FS API?
>

It would require some custom code like "create greek tree,
create txn, modify a few nodes" on one side and "open the
only available txn, commit txn" on the other side.

> Or can some tool such as svnmucc already do this?
>

svnadmin can only list and remove txns. svnmucc

> I presume you rely on apr_off_t, not off_t, right?

Yes, I always use apr_off_t. On my system, APR typedefs
it as off_t.

> I.e. it's
> enough to recompile APR and SVN with or without large file
> support to switch between 32bit and 64bit apr_off_t?
>

It will be enough if it changes sizeof(apr_off_t).

-- Stefan^2.
Received on 2014-09-30 11:44:35 CEST

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