From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
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To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: 9.3: load path to mitigate load penalty for checksums |
Date: | 2012-06-06 19:08:05 |
Message-ID: | CA+TgmoaSVH8jWPgKB8zxcAvH=7v2wLG1AfKiHNBi1Ae5JHFc8A@mail.gmail.com |
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Lists: | pgsql-hackers |
On Mon, Jun 4, 2012 at 9:26 PM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> Thoughts?
Simon already proposed a way of doing this that doesn't require
explicit user action, which seems preferable to a method that does
require explicit user action, even though it's a little harder to
implement. His idea was to store the XID of the process creating the
table in the pg_class row, which I think is *probably* better than
your idea of having a process that waits and then flips the flag.
There are some finicky details though - see previous thread for
discussion of some of the issues.
It would be very nice to have a method that detects whether or not
there is only one open snapshot in a particular backend. Any time
that condition is met, tuples written into a table created or
truncated in the current transaction can be written with
HEAP_XMIN_COMMITTED already set. That is not as nice as being able to
set HEAP_XMIN_COMMITTED *and* PD_ALL_VISIBLE *and* the visibility map,
but it would still be a big improvement over the status quo. I would
like to see us get that part done and committed and then worry about
writing the tuples with PD_ALL_VISIBLE set as a separate project. In
many cases it would also be nice to write the tuples pre-frozen, so I
think we should look for a design that will support that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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