On 2005-05-30, Neil Conway <[EMAIL PROTECTED]> wrote:
> On Wed, 2005-03-23 at 10:04 -0500, Tom Lane wrote:
>> I think last night's discussion makes it crystal-clear why I felt that
>> this hasn't been sufficiently thought through. Please revert until the
>> discussion comes to a conclusion.
>
> Ar
Neil Conway <[EMAIL PROTECTED]> writes:
> Are there any remaining objections to reapplying this patch?
> The original commit message is here:
> http://archives.postgresql.org/pgsql-committers/2005-03/msg00316.php
> The archives of the -hackers thread are here:
> http://archives.postgresql.org/pgsql
On Wed, 2005-03-23 at 10:04 -0500, Tom Lane wrote:
> I think last night's discussion makes it crystal-clear why I felt that
> this hasn't been sufficiently thought through. Please revert until the
> discussion comes to a conclusion.
Are there any remaining objections to reapplying this patch?
Th
Alvaro Herrera wrote:
> On Wed, Mar 23, 2005 at 10:42:01AM +0800, Christopher Kings-Lynne wrote:
> > >>If you want to be my friend forever, then fix CLUSTER so that it uses
> > >>sharerowexclusive as well :D
> > >
> > >I don't think it's as easy as that, because you have to move tuples
> > >around
Tom Lane wrote:
I agree that we aren't MVCC with respect to DDL operations (and for this
purpose CLUSTER is DDL). Trying to become so would open a can of worms
far larger than it's worth, though, IMHO.
I think if we can come up with a reasonable way to handle all the
consequences, it's worth doin
Tom Lane wrote:
I think last night's discussion makes it crystal-clear why I felt that
this hasn't been sufficiently thought through. Please revert until the
discussion comes to a conclusion.
I applied the patch because I don't think it is very closely related to
the discussion. But if you'd pref
Neil Conway <[EMAIL PROTECTED]> writes:
> Tom Lane wrote:
>> It isn't 100% MVCC, I agree. But it works because system catalog
>> lookups are SnapshotNow, and so when another session comes and wants to
>> look at the table it will see the committed new version of the pg_class
>> row pointing at the
Neil Conway <[EMAIL PROTECTED]> writes:
> Tom Lane wrote:
>> I don't think this has been adequately thought through at all ... but
>> at least make it ExclusiveLock. What is the use-case for allowing
>> SELECT FOR UPDATE in parallel with this?
> Ok, patch applied -- I adjusted it to use Exclusive
Neil Conway <[EMAIL PROTECTED]> writes:
> Tom Lane wrote:
> > It isn't 100% MVCC, I agree. But it works because system catalog
> > lookups are SnapshotNow, and so when another session comes and wants to
> > look at the table it will see the committed new version of the pg_class
> > row pointing a
> > It would keep the old table around while building the new, then grab
> > an exclusive lock to swap the two.
>
> Lock upgrading is right out.
It would need a whole of new family of "intent" locks, with different rules.
Andreas
---(end of broadcast)
Tom Lane wrote:
I don't think this has been adequately thought through at all ... but
at least make it ExclusiveLock. What is the use-case for allowing
SELECT FOR UPDATE in parallel with this?
Ok, patch applied -- I adjusted it to use ExclusiveLock, and fleshed out
some of the comments.
-Neil
In
Tom Lane wrote:
This is presuming that we abandon the notion that system catalog
access use SnapshotNow. Which opens the question of what they should
use instead ... to which "transaction snapshot" isn't the answer,
because we have to be able to do system catalog accesses before
we've set the snap
Tom Lane wrote:
It isn't 100% MVCC, I agree. But it works because system catalog
lookups are SnapshotNow, and so when another session comes and wants to
look at the table it will see the committed new version of the pg_class
row pointing at the new relfilenode file.
If by "works", you mean "provid
Neil Conway <[EMAIL PROTECTED]> writes:
> - if we make these changes, we will need some way to delete a
> no-longer-visible relfilenode.
This is presuming that we abandon the notion that system catalog
access use SnapshotNow. Which opens the question of what they should
use instead ... to which
Neil Conway <[EMAIL PROTECTED]> writes:
> How can we drop the file at commit, given that a serializable
> transaction's snapshot should still be able to see old relfilenode's
> content?
It isn't 100% MVCC, I agree. But it works because system catalog
lookups are SnapshotNow, and so when another
Neil Conway wrote:
> Tom Lane wrote:
> > Utterly wrong. When you commit you will physically drop the old table.
> > If there is a SELECT running against the old table it will be quite
> > unhappy after that.
>
> How can we drop the file at commit, given that a serializable
> transaction's snapsh
Tom Lane wrote:
Utterly wrong. When you commit you will physically drop the old table.
If there is a SELECT running against the old table it will be quite
unhappy after that.
How can we drop the file at commit, given that a serializable
transaction's snapshot should still be able to see old relfi
Neil Conway <[EMAIL PROTECTED]> writes:
> Well, we will be holding an ExclusiveLock on the heap relation
> regardless. We "replace" the heap table by swapping its relfilenode, so
> ISTM we needn't hold an AccessExclusiveLock.
Utterly wrong. When you commit you will physically drop the old table
Neil Conway wrote:
... except that when we rebuild the relation's indexes, we acquire an
AccessExclusiveLock on the index. This would introduce the risk of
deadlock. It seems necessary to acquire an AccessExclusiveLock when
rebuilding shared indexes, since we do the index build in-place, but I
Christopher Kings-Lynne <[EMAIL PROTECTED]> writes:
> It would keep the old table around while building the new, then grab
> an exclusive lock to swap the two.
Lock upgrading is right out.
regards, tom lane
---(end of broadcast)-
Neil Conway <[EMAIL PROTECTED]> writes:
> /*
> ! * Grab an exclusive lock on the pk table, so that someone doesn't
> ! * delete rows out from under us. (Although a lesser lock would do for
> ! * that purpose, we'll need exclusive lock anyway to add triggers to
> ! * the
Neil Conway <[EMAIL PROTECTED]> writes:
>> AndrewSN pointed out on IRC that ALTER TABLE ... ADD FOREIGN KEY and
>> CREATE TRIGGER both acquire AccessExclusiveLocks on the table they are
>> adding triggers to (the PK table, in the case of ALTER TABLE). Is this
>> necessary? I don't see why we can
Bruce Momjian wrote:
Certainly we need to upgrade to an exclusive table lock to replace the
heap table.
Well, we will be holding an ExclusiveLock on the heap relation
regardless. We "replace" the heap table by swapping its relfilenode, so
ISTM we needn't hold an AccessExclusiveLock.
Do we want t
Neil Conway wrote:
> So I think it should be possible to lock both the heap relation and the
> index with ExclusiveLock, which would allow SELECTs on them. This would
> apply to both the single relation and multiple relation variants of
> CLUSTER (since we do each individual clustering in its ow
Huh, cluster already does that.
It does and it doesn't. Something like the first thing it does is muck
with the old table's filenode IIRC, meaning that immediately the old
table will no longer work.
Chris
---(end of broadcast)---
TIP 8: explain an
Christopher Kings-Lynne wrote:
If you want to be my friend forever, then fix CLUSTER so that it uses
sharerowexclusive as well :D
Hmm, this might be possible as well. During a CLUSTER, we currently
- lock the heap relation with AccessExclusiveLock
- lock the index we're clustering on with AccessEx
On Wed, Mar 23, 2005 at 10:42:01AM +0800, Christopher Kings-Lynne wrote:
> >>If you want to be my friend forever, then fix CLUSTER so that it uses
> >>sharerowexclusive as well :D
> >
> >I don't think it's as easy as that, because you have to move tuples
> >around in the cluster operation. Same s
If you want to be my friend forever, then fix CLUSTER so that it uses
sharerowexclusive as well :D
I don't think it's as easy as that, because you have to move tuples
around in the cluster operation. Same sort of issue as vacuum full I would
suggest.
Cluster doesn't move rows...
I didn't say it
On Wed, 23 Mar 2005 12:40 pm, Christopher Kings-Lynne wrote:
> If you want to be my friend forever, then fix CLUSTER so that it uses
> sharerowexclusive as well :D
>
I don't think it's as easy as that, because you have to move tuples
around in the cluster operation. Same sort of issue as vacuum
If you want to be my friend forever, then fix CLUSTER so that it uses
sharerowexclusive as well :D
Chris
Neil Conway wrote:
Neil Conway wrote:
AndrewSN pointed out on IRC that ALTER TABLE ... ADD FOREIGN KEY and
CREATE TRIGGER both acquire AccessExclusiveLocks on the table they are
adding trigg
Neil Conway wrote:
AndrewSN pointed out on IRC that ALTER TABLE ... ADD FOREIGN KEY and
CREATE TRIGGER both acquire AccessExclusiveLocks on the table they are
adding triggers to (the PK table, in the case of ALTER TABLE). Is this
necessary? I don't see why we can't allow SELECT queries on the ta
Neil Conway wrote:
AndrewSN pointed out on IRC that ALTER TABLE ... ADD FOREIGN KEY and
CREATE TRIGGER both acquire AccessExclusiveLocks on the table they are
adding triggers to (the PK table, in the case of ALTER TABLE). Is this
necessary? I don't see why we can't allow SELECT queries on the ta
AndrewSN pointed out on IRC that ALTER TABLE ... ADD FOREIGN KEY and
CREATE TRIGGER both acquire AccessExclusiveLocks on the table they are
adding triggers to (the PK table, in the case of ALTER TABLE). Is this
necessary? I don't see why we can't allow SELECT queries on the table to
proceed whi
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