Atomic I/Os, Transactions

[Howard Chu <hyc@symas.com>]

Since atomic I/Os have come up recently, I thought I'd throw a wish-list item 
out there for consideration. It seems to me that the notion of write barriers 
was too heavy-handed. What I would like is a way to tag groups of writes. The 
only ordering constraint being, writes within a group tagged N cannot be 
started before all writes in group N-1 have completed. Aside from that, writes 
within a group may be freely mixed and reordered with non-tagged/non-grouped 
writes, and freely reordered within the group. That would allow a DB 
application to commit its transactions with a consistent ordering without 
requiring a full cache flush/sync/etc., thus reducing impact on overall I/O.

-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/