On 6/19/20 11:48 AM, Amit Kapila wrote:
On Wed, Jun 10, 2020 at 8:36 AM Andrey V. Lepikhov
<a.lepik...@postgrespro.ru> wrote:
On 09.06.2020 11:41, Fujii Masao wrote:
The patches seem not to be registered in CommitFest yet.
Are you planning to do that?
Not now. It is a sharding-related feature. I'm not sure that this
approach is fully consistent with the sharding way now.
Can you please explain in detail, why you think so? There is no
commit message explaining what each patch does so it is difficult to
understand why you said so?
For now I used this patch set for providing correct visibility in the
case of access to the table with foreign partitions from many nodes in
parallel. So I saw at this patch set as a sharding-related feature, but
[1] shows another useful application.
CSN-based approach has weak points such as:
1. Dependency on clocks synchronization
2. Needs guarantees of monotonically increasing of the CSN in the case
of an instance restart/crash etc.
3. We need to delay increasing of OldestXmin because it can be needed
for a transaction snapshot at another node.
So I do not have full conviction that it will be better than a single
distributed transaction manager.
Also, can you let us know if this
supports 2PC in some way and if so how is it different from what the
other thread on the same topic [1] is trying to achieve?
Yes, the patch '0003-postgres_fdw-support-for-global-snapshots' contains
2PC machinery. Now I'd not judge which approach is better.
Also, I
would like to know if the patch related to CSN based snapshot [2] is a
precursor for this, if not, then is it any way related to this patch
because I see the latest reply on that thread [2] which says it is an
infrastructure of sharding feature but I don't understand completely
whether these patches are related?
I need some time to study this patch. At first sight it is different.
Basically, there seem to be three threads, first, this one and then
[1] and [2] which seems to be doing the work for sharding feature but
there is no clear explanation anywhere if these are anyway related or
whether combining all these three we are aiming for a solution for
atomic commit and atomic visibility.
It can be useful to study all approaches.
I am not sure if you know answers to all these questions so I added
the people who seem to be working on the other two patches. I am also
afraid that if there is any duplicate or conflicting work going on in
these threads so we should try to find that as well.
Ok
[1] -
https://www.postgresql.org/message-id/CA%2Bfd4k4v%2BKdofMyN%2BjnOia8-7rto8tsh9Zs3dd7kncvHp12WYw%40mail.gmail.com
[2] - https://www.postgresql.org/message-id/2020061911294657960322%40highgo.ca
[1]
https://www.postgresql.org/message-id/flat/20200301083601.ews6hz5dduc3w2se%40alap3.anarazel.de
--
Andrey Lepikhov
Postgres Professional
https://postgrespro.com
