On Mon, Jun 6, 2011 at 12:19 AM, Itagaki Takahiro <itagaki.takah...@gmail.com> wrote: > On Sun, Jun 5, 2011 at 12:03, Robert Haas <robertmh...@gmail.com> wrote: >> If other buffer pins do exist, then we can't >> defragment the page, but that doesn't mean no useful work can be done: >> we can still mark used line pointers dead, or dead line pointers >> unused. We cannot defragment, but that can be done either by the next >> VACUUM or by a HOT cleanup. > > This is just an idea -- Is it possible to have copy-on-write techniques? > VACUUM allocates a duplicated page for the pinned page, and copy valid > tuples into the new page. Following buffer readers after the VACUUM will > see the cloned page instead of the old pinned one.
Heikki suggested the same thing, and it's not a bad idea, but I think it would be more work to implement than what I proposed. The caller would need to be aware that, if it tries to re-acquire a content lock on the same page, the offset of the tuple within the page might change. I'm not sure how much work would be required to cope with that possibility. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
