Re: reiser4 data journalling?

[Hans Reiser <reiser@namesys.com>]

Lars Marowsky-Bree wrote:

>On 2003-08-28T20:18:14,
>   Tom Vier <tmv@comcast.net> said:
>
>  
>
>>and shell builtins would have to be modded to insure page alignment. it
>>would be neat if all the regular builtins (cp, mv, ln) were atomic.
>>    
>>
>
>mv (ie, rename), ln and rm have always been atomic. That's a POSIX
>requirement.
>
Programs that need atomicity find it inconvenient that only one mv, or 
one ln, and or one rm, or one 4k write of a block, are atomic operations.

>The new thing with reiserfs4 seems to be that if you do a write of, say,
>1M size in the atomic way, 
>

>another reading process will either see all
>of the write or none of the write to have taken place.
>
No, isolation is not yet implemented and won't be unless we come up with 
some more funding from somewhere.  The txnmgr seems to be structured to 
handle isolation, but....

The new thing with reiser4 is that if you do that write of 1MB to a 
file, and perhaps updates to 63 other files as well, as part of an atom, 
it will either all survive a crash, or none of it will.  We have 
considered using the term "transcrash" for this.

>(Right now, you could see a 'partial' read, where some pages from the
>write have been written already while others return the old data.)
>
>And apparently, you can say "begin transaction" and "commit / abort
>transaction" to achieve the same for multiple operations as a group.
>
>Hans, does that support nested transactions, too?
>
>And one thing has slipped from my mind: How do I enter a transaction? is
>it like chroot(), or a task-specific thing, how can child processes
>participate in the transaction etc?
>
>
>Sincerely,
>    Lars Marowsky-Brée <lmb@suse.de>
>
>  
>


-- 
Hans