On Aug 15, 2007, at 1:54 PM, Gregory Stark wrote:
A third idea would be for a heap scan to check if all rows are
visible
and if so set a per-table flag which can be checked by index
scans.
Any change to the table would have to clear the flag. To detect
changes during the heap scan a counter could be set at the
start and
checked at the end --- if it is the same, the table has not been
modified --- any table change would increment the counter.
I think I would prefer to address this in the same infrastructure
as the
dead-space-map. That way you're not dependent on having no updates
happening
on the table at all. Any tuples on pages which contain no in-doubt
tuples
could have their visibility check skipped but when you come across
a tuple on
a page which has been modified since the last vacuum then you have
to check
the visibility.
The advantage to Bruce's idea is that it sounds pretty simple to
implement. While it wouldn't be of use for many general cases, it
*would* be useful for read-only tables, ie: old partitions.
--
Decibel!, aka Jim Nasby [EMAIL PROTECTED]
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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