Unique transaction names and revision number (was Re: [PATCH] Remove APR ICONV dependency on Windows)

On 7/8/07, Ivan Zhakov <chemodax@gmail.com> wrote:
> On 7/8/07, D.J. Heap <djheap@gmail.com> wrote:
> > On 7/7/07, Ivan Zhakov <chemodax@gmail.com> wrote:
> > [snip]
> > > And of course primary question: Does it work without my patch? Because
> > > these failures can be related to new txn generation code, committed by
> > > Blair in r25430.
> > >
> >
> >
> > I'm building with trunk r25679 and after backing out r25650, the
> > fs-test.exe passes all tests again. So, either the patch is bringing
> > out some lurking problem, or it is affecting the fs stuff in some way
> > I can't seem to figure out.
> >
> It seems I found way to reproduce problem even without my patch. Many
> fs-test will fail on Windows if you just remove time part from
> generated transaction name in fs_fs. See patch:
>
> Index: subversion/libsvn_fs_fs/fs_fs.c
> ===================================================================
> --- subversion/libsvn_fs_fs/fs_fs.c (revision 25654)
> +++ subversion/libsvn_fs_fs/fs_fs.c (working copy)
> @@ -3195,7 +3195,7 @@
> *p = '-';
>
> process_id = getpid();
> - now = apr_time_now();
> + now = 0; /* It's for testing purposes only! should apr_time_now(). */
>
> unique_basename = apr_psprintf(pool, "%s-%05d-%" APR_TIME_T_FMT,
> hostname_str, process_id, now);
> Index: subversion/libsvn_subr/utf.c
> ===================================================================
> --- subversion/libsvn_subr/utf.c (revision 25654)
> +++ subversion/libsvn_subr/utf.c (working copy)
> @@ -253,7 +253,7 @@
> pool = apr_hash_pool_get(xlate_handle_hash);
>
> /* Try to create a handle. */
> -#if defined( WIN32)
> +#if 0
> apr_err = svn_subr__win32_xlate_open(&handle, topage, frompage, pool);
> #elif defined(AS400)
> apr_err = apr_xlate_open(&handle, (int)topage, (int)frompage, pool);
>
> So it seems the problem of my patch that it made running Subversion
> faster and we got two transactions in the same time :)
>
> Now I'm trying to figure out why this transaction generation code
> fails on Windows.
>
It seems I understand what is happen here.
Before r25430 we've been generated transaction named
"<rev>-<uniquifier>". After r25430 we tried to guarantee transaction
names to be unique and added hostname, pid and time to transaction
name. And for optimization we removed revision number from txn name.
So we got "<hostname>-<pid>-<time>-<uniquifier>" txn names.

Looks good, but bad news that this form of txn names isn't guarantee
to be unique. At least on Windows, where apr_time_now() could return
the same time for different transactions.

And we are fail because fsfs assumes that transaction names unique
between revisions! So it MUST include revision number.

So we have to problems:
1. transaction names still isn't guaranteed to be unique
2. fsfs depends that transaction names unique between revisions, i.e.
include revision number.

-- 
Ivan Zhakov
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