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Re: revprop packing: why aren't _all_ revprops packed?

From: Mark Phippard <markphip_at_gmail.com>
Date: Fri, 1 Jul 2011 09:27:57 -0400

On Fri, Jul 1, 2011 at 9:22 AM, Daniel Shahaf <danielsh_at_elego.de> wrote:
> Mark Phippard wrote on Fri, Jul 01, 2011 at 09:10:31 -0400:
>> On Thu, Jun 30, 2011 at 5:21 PM, Peter Samuelson <peter_at_p12n.org> wrote:
>> >
>> > [kmradke_at_rockwellcollins.com]
>> >> I would love to have revprop packing, but not at the cost of
>> >> potentially disabling the use of traditional backup software.
>> >>
>> >> Is there a way to disable fsfs revprop packing, or at least have
>> >> it function in an atomic way like the regular rev packing?
>> >
>> > Hijacking the thread to veer _slightly_ off topic:
>> >
>> > Why is revprop packing an explicit 'svnadmin pack' operation?  If we
>> > agree to put revprops in sqlite, why not do that from the start?  Just
>> > open the shard-specific sqlite file, creating it if necessary, and
>> > write the new set of revprops there.  No distinction between packed and
>> > unpacked revprops, no 'min-unpacked-revprop' file.
>> >
>> > Was there a good reason not to do it that way?
>>
>> Wouldn't the concerns that Kevin has raised kick in if we did this?
>> Basically you could not do a safe backup of a repository because if a
>> commit happens during the backup we will be writing to the SQLite
>> database.
>>
>
> They would.
>
>
> For the record, some ways to solve that concern are --
>
> 1. hotcopy
> 2. take an atomic diks snapshot
> 3. teach FSFS to pack revision shards without packing revprop shards
> 4. backup just revprops.db in the SQLite-safe way
>   (grab an SQLite-level lock, cp(1), release lock)

I guess I am confused then. Especially after reading the issue you
filed. This is how I interpret this, which maybe wrong.

1) Kevin raised some concerns about revprop packing and backup.

2) After some back and forth, I think the conclusion was that given
the way it is currently implemented there is not much danger. It is
pretty easy to do a clean backup safely.

3) Rather than all go back to our normal lives, we have decided we
should block the release until we can make changes so that revprop
packing and backups will now be very dangerous and all of Kevin's
concerns are now valid.

How does this make sense?

I thought the only proposal we were going to consider was Ivan's
proposal to get rid of SQLite entirely and just use normal packed
files as we do for the revisions.

-- 
Thanks
Mark Phippard
http://markphip.blogspot.com/
Received on 2011-07-01 15:28:32 CEST

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