Question about building an exportable snapshop
While working on the issue [1]/messages/by-id/CAFiTN-tqopqpfS6HHug2nnOGieJJ_nm-Nvy0WBZ=Zpo-LqtSJA@mail.gmail.com, I realize that if a subtransaction
hasn't done any catalog change then we don't add this in the commit
xid list even if we are building a full snapshot [2]/* * Add subtransaction to base snapshot if catalog modifying, we don't * distinguish to toplevel transactions there. */ if (ReorderBufferXidHasCatalogChanges(builder->reorder, subxid)) { sub_needs_timetravel = true; needs_snapshot = true;. That means when
we will convert this to the MVCC snapshot we will add this to a
running xid list. If my understanding is correct then how visibility
will work? Because if I look at the code in XidInMVCCSnapshot(), then
if the suboverflowed is not set then first we are going to look into
the snapshot->subxip array and if we don't find it there then we look
into the snapshot->xip array, and now we will be finding even
committed subxips in the snapshot->xip array. Am I missing something?
[2]: /* * Add subtransaction to base snapshot if catalog modifying, we don't * distinguish to toplevel transactions there. */ if (ReorderBufferXidHasCatalogChanges(builder->reorder, subxid)) { sub_needs_timetravel = true; needs_snapshot = true;
/*
* Add subtransaction to base snapshot if catalog modifying, we don't
* distinguish to toplevel transactions there.
*/
if (ReorderBufferXidHasCatalogChanges(builder->reorder, subxid))
{
sub_needs_timetravel = true;
needs_snapshot = true;
[3]:
[1]: /messages/by-id/CAFiTN-tqopqpfS6HHug2nnOGieJJ_nm-Nvy0WBZ=Zpo-LqtSJA@mail.gmail.com
--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com
On Tue, Oct 12, 2021 at 6:21 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
While working on the issue [1], I realize that if a subtransaction
hasn't done any catalog change then we don't add this in the commit
xid list even if we are building a full snapshot [2].
I think this is true only if we have reached SNAPBUILD_CONSISTENT
state otherwise, we are adding subtransactions in the committed xip
array by setting 'needs_timetravel' to true. And if we have already
reached a consistent state before it then we anyway don't need to add
this. If this is true, do you still see any problem?
--
With Regards,
Amit Kapila.
On Wed, Oct 20, 2021 at 5:06 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
On Tue, Oct 12, 2021 at 6:21 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
While working on the issue [1], I realize that if a subtransaction
hasn't done any catalog change then we don't add this in the commit
xid list even if we are building a full snapshot [2].I think this is true only if we have reached SNAPBUILD_CONSISTENT
state otherwise, we are adding subtransactions in the committed xip
array by setting 'needs_timetravel' to true. And if we have already
reached a consistent state before it then we anyway don't need to add
this. If this is true, do you still see any problem?
Yeah, you are right.
--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com