[svn.haxx.se] · SVN Dev · SVN Users · SVN Org · TSVN Dev · TSVN Users · Subclipse Dev · Subclipse Users · this month's index

Re: obliterate in trunk (was: svn commit: r39745 - trunk/subversion/svn)

From: Julian Foad <julianfoad_at_btopenworld.com>
Date: Mon, 12 Oct 2009 12:24:24 +0100

Daniel Shahaf wrote:
> [ couldn't sleep ]

Heh. That's sometimes when the clearest thoughts come.

> Daniel Shahaf wrote on Sat, 10 Oct 2009 at 14:31 +0200:
> > Julian Foad wrote on Sat, 10 Oct 2009 at 01:55 +0100:
> > > Add an initial skeleton implementation for "svn obliterate", with the UI
> > > and public API changes hidden behind #ifdef SVN_WITH_EXPERIMENTAL_OBLITERATE.
> > >
> > > ...
> > >
> > > Index: subversion/libsvn_fs_fs/fs_fs.c
> > > ===================================================================
> > > --- subversion/libsvn_fs_fs/fs_fs.c (revision 39914)
> > > +++ subversion/libsvn_fs_fs/fs_fs.c (working copy)
> > > @@ -5885,6 +6025,45 @@ svn_fs_fs__commit(svn_revnum_t *new_rev_
> > > }
> > >
> > > svn_error_t *
> > > +svn_fs_fs__commit_obliteration(svn_revnum_t rev,
> > > + svn_fs_t *fs,
> > > + svn_fs_txn_t *txn,
> > > + apr_pool_t *pool)
> > > +{
> > > + struct commit_baton cb;
> > > + fs_fs_data_t *ffd = fs->fsap_data;
> > > +
> > > + /* Analogous to svn_fs_fs__commit(). */
> > > + cb.new_rev_p = &rev;
> > > + cb.fs = fs;
> > > + cb.txn = txn;
> > > +
> > > + if (ffd->rep_sharing_allowed)
> > > + {
> > > + cb.reps_to_cache = apr_array_make(pool, 5, sizeof(representation_t *));
> > > + cb.reps_pool = pool;
> > > + }
> > > + else
> > > + {
> > > + cb.reps_to_cache = NULL;
> > > + cb.reps_pool = NULL;
> > > + }
> > > +
> > > + SVN_ERR(svn_fs_fs__with_write_lock(fs, commit_obliteration_body, &cb, pool));
> > > +
> > > + if (ffd->rep_sharing_allowed)
> > > + {
> > > + /* ### TODO: ignore errors opening the DB (issue #3506) * */
> > > + SVN_ERR(svn_fs_fs__open_rep_cache(fs, pool));
> > > + SVN_ERR(svn_sqlite__with_transaction(ffd->rep_cache_db,
> > > + commit_sqlite_txn_callback,
> > > + &cb, pool));
> > > + }
> > > +
> >
> > [ I think you know this already, but I'll say it anyway. ]

Thanks for saying this: I don't yet have this level of awareness. I'm
learning the whole repository and FSFS side as I go along. I'm very
grateful for your eyes on this.

> > Half of the lines of this function deal with storing new reps in the
> > rep-cache DB. Some day it should also remove the old DB rows (and
> > somehow cause references in other revisions into the revision-being-
> > obliterated to still work).

When you say "cache", is it a cache in the sense that functionally it
doesn't matter whether it contains any or all of these things? From what
you ssay below, it sounds like it is a "rep store". Please let me
understand that clearly before I go on.

> Actually, after r39897, it's possible that DB rows referencing the
> revision-being-obliterated[1] will be added at an arbitrary time after
> that revision has been committed: it's (theoretically, depending on
> the order SQLite hands out write locks) possible that the sequence
>
> # make a few large (multi-file) commits
> # commit rBO
> # obliterate rBO
> # wait 3 seconds
>
> will result in rep-cache rows referring the obliterated version of rBO.
>
>
> Not sure how to solve that. We want to ensure that the obliterate doesn't
> get the SQLite write lock before "its" commit gets the same lock. [2]
>
>
> Possible damage? If the DB rows relating to the original rBO are added
> after its obliteration its complete, then reps created in the future may
> rely on these rows and avoid writing themselves out explicitly --- even
> though the reps may no longer be in the rBO rev file.

Thanks for the other comments, which I believe I have addressed in what
I committed in r39949.

- Julian

------------------------------------------------------
http://subversion.tigris.org/ds/viewMessage.do?dsForumId=462&dsMessageId=2406584
Received on 2009-10-12 13:25:05 CEST

This is an archived mail posted to the Subversion Dev mailing list.