Jeff Davis wrote:
On Tue, 2010-03-16 at 15:29 +, Greg Stark wrote:
I'm picturing storing a bit in the visibility map indicating that *no*
records are visible in a given page.
I've been thinking for a while that we could store the visibility
information in a structure separate from the
On Mon, 2010-03-22 at 16:48 -0400, Bruce Momjian wrote:
I don't think we want to move to 64-bit xids becasue we would still need
to do vacuum freeze to trim the clog. In fact we do vacuum freeze much
more frequently than required for 32-bit xids for this very reason.
Good point. I think there
Surely the VM is already update-friendly. If you update a tuple in a
page with the visibility bit set, the bit must be unset or you will get
wrong results.
I was referring in the context of index only scans to skip visibility
checks. I doubt, whether the visibility map feature to skip
On Thu, Mar 18, 2010 at 2:50 AM, Tom Lane t...@sss.pgh.pa.us wrote:
Jeff Davis pg...@j-davis.com writes:
There are all kinds of challenges there, but it might be worth thinking
about. Visibility information is highly compressible, and requires
constant maintenance (updates, deletes,
Secondly there's the whole retail vacuum problem -- any
index entries referring to this page would be left dangling unless
there's some kind of retail vacuum or perhaps a page version number.
The issue, we can divide into two
a)volatile functions
b)broken datatypes
For a) I think volatile
I didn't mean that we'd want to compress it to the absolute minimum
size. I had envisioned that it would be a simple scheme designed only to
eliminate long runs of identical visibility information (perhaps only
the frozen and always visible regions would be compressed).
The extra level of
si...@2ndquadrant.com (Simon Riggs) writes:
On Tue, 2010-03-16 at 15:29 +, Greg Stark wrote:
big batch delete
Is one of the reasons for partitioning, allowing the use of truncate.
Sure, but it would be even nicer if DELETE could be thus made cheaper
without needing to interfere with the
On Thu, 2010-03-18 at 14:29 +0530, Gokulakannan Somasundaram wrote:
If you want it to be cheaply updatable (or even cheaply
readable),
compression is not what you're going to do.
regards, tom lane
The visibility map itself is already an example of compression. If
visibility information were randomly distributed among tuples, the
visibility map would be nearly useless.
I believe it is very difficult to make visibility map update friendly
without compromising durability. But such a
On Fri, 2010-03-19 at 01:59 +0530, Gokulakannan Somasundaram wrote:
The visibility map itself is already an example of
compression. If
visibility information were randomly distributed among tuples,
the
visibility map would be nearly useless.
Jeff Davis pg...@j-davis.com writes:
On Fri, 2010-03-19 at 01:59 +0530, Gokulakannan Somasundaram wrote:
I believe it is very difficult to make visibility map update friendly
without compromising durability. But such a functionality is very
much wanted in PG still.
Surely the VM is already
On Thu, 2010-03-18 at 16:50 -0400, Tom Lane wrote:
The VM is (a) not compressed and (b) not correctness-critical.
Wrong bit values don't do any serious damage.
The VM cause wrong results if a bit is set that's not supposed to be --
right? Am I missing something? How does a seq scan skip
On Thu, Mar 18, 2010 at 15:07, Jeff Davis pg...@j-davis.com wrote:
On Thu, 2010-03-18 at 16:50 -0400, Tom Lane wrote:
The VM is (a) not compressed and (b) not correctness-critical.
Wrong bit values don't do any serious damage.
The VM cause wrong results if a bit is set that's not supposed to
Jeff Davis pg...@j-davis.com writes:
On Thu, 2010-03-18 at 16:50 -0400, Tom Lane wrote:
The VM is (a) not compressed and (b) not correctness-critical.
Wrong bit values don't do any serious damage.
The VM cause wrong results if a bit is set that's not supposed to be --
right? Am I missing
On Thu, Mar 18, 2010 at 9:07 PM, Jeff Davis pg...@j-davis.com wrote:
The VM cause wrong results if a bit is set that's not supposed to be --
right? Am I missing something? How does a seq scan skip visibility
checks and still produce right results, if it doesn't rely on the bit?
There's also a
On Thu, 2010-03-18 at 17:17 -0400, Tom Lane wrote:
The VM cause wrong results if a bit is set that's not supposed to be --
right? Am I missing something? How does a seq scan skip visibility
checks and still produce right results, if it doesn't rely on the bit?
It doesn't. The only thing
On Thu, 2010-03-18 at 14:48 -0700, Jeff Davis wrote:
On Thu, 2010-03-18 at 17:17 -0400, Tom Lane wrote:
The VM cause wrong results if a bit is set that's not supposed to be --
right? Am I missing something? How does a seq scan skip visibility
checks and still produce right results, if it
Jeff Davis pg...@j-davis.com writes:
I tested in gdb, and it calls HeapTupleSatisfiesMVCC, until I VACUUM a
few times, and then it doesn't call it any more. So, apparently the seq
scan optimization _is_ there. And that means it is correctness-critical.
The page header bit is critical. Not the
On Tue, 2010-03-16 at 15:29 +, Greg Stark wrote:
big batch delete
Is one of the reasons for partitioning, allowing the use of truncate.
--
Simon Riggs www.2ndQuadrant.com
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your
On Tue, 2010-03-16 at 15:29 +, Greg Stark wrote:
I'm picturing storing a bit in the visibility map indicating that *no*
records are visible in a given page.
I've been thinking for a while that we could store the visibility
information in a structure separate from the heap -- sort of like
Jeff Davis pg...@j-davis.com writes:
There are all kinds of challenges there, but it might be worth thinking
about. Visibility information is highly compressible, and requires
constant maintenance (updates, deletes, freezing, etc.). It also might
make it possible to move to 64-bit xids, if we
On Wed, 2010-03-17 at 17:20 -0400, Tom Lane wrote:
Jeff Davis pg...@j-davis.com writes:
There are all kinds of challenges there, but it might be worth thinking
about. Visibility information is highly compressible, and requires
constant maintenance (updates, deletes, freezing, etc.). It also
On Wed, 2010-03-17 at 14:09 -0700, Jeff Davis wrote:
I've been thinking for a while that we could store the visibility
information in a structure separate from the heap -- sort of like the
visibility map, but per-tuple and authoritative rather than a per-page
hint.
A lot of people have been
Greg Stark st...@mit.edu writes:
However then I started thinking about this case and wondered if it
wouldn't be possible to optimize. One of the suggested optimizations
was to look at using TRUNCATE. But I wonder why it's necessary to use
a dedicated command. Shouldn't it be possible for the
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