On Fri, Aug 26, 2016 at 11:37 AM, Masahiko Sawada <sawada.m...@gmail.com> wrote:
> On Fri, Aug 26, 2016 at 3:03 PM, Ashutosh Bapat > <ashutosh.ba...@enterprisedb.com> wrote: > > > > > > On Fri, Aug 26, 2016 at 11:22 AM, Masahiko Sawada <sawada.m...@gmail.com > > > > wrote: > >> > >> On Fri, Aug 26, 2016 at 1:32 PM, Vinayak Pokale <vinpok...@gmail.com> > >> wrote: > >> > Hi All, > >> > > >> > Ashutosh proposed the feature 2PC for FDW for achieving atomic commits > >> > across multiple foreign servers. > >> > If a transaction make changes to more than two foreign servers the > >> > current > >> > implementation in postgres_fdw doesn't make sure that either all of > them > >> > commit or all of them rollback their changes. > >> > > >> > We (Masahiko Sawada and me) reopen this thread and trying to > contribute > >> > in > >> > it. > >> > > >> > 2PC for FDW > >> > ============ > >> > The patch provides support for atomic commit for transactions > involving > >> > foreign servers. when the transaction makes changes to foreign > servers, > >> > either all the changes to all the foreign servers commit or rollback. > >> > > >> > The new patch 2PC for FDW include the following things: > >> > 1. The patch 0001 introduces a generic feature. All kinds of FDW that > >> > support 2PC such as oracle_fdw, mysql_fdw, postgres_fdw etc. can > involve > >> > in > >> > the transaction. > >> > > >> > Currently we can push some conditions down to shard nodes, especially > in > >> > 9.6 > >> > the directly modify feature has > >> > been introduced. But such a transaction modifying data on shard node > is > >> > not > >> > executed surely. > >> > Using 0002 patch, that modify is executed with 2PC. It means that we > >> > almost > >> > can provide sharding solution using > >> > multiple PostgreSQL server (one parent node and several shared node). > >> > > >> > For multi master, we definitely need transaction manager but > transaction > >> > manager probably can use this 2PC for FDW feature to manage > distributed > >> > transaction. > >> > > >> > 2. 0002 patch makes postgres_fdw possible to use 2PC. > >> > > >> > 0002 patch makes postgres_fdw to use below APIs. These APIs are > generic > >> > features which can be used by all kinds of FDWs. > >> > > >> > a. Execute PREAPRE TRANSACTION and COMMIT/ABORT PREAPRED instead > of > >> > COMMIT/ABORT on foreign server which supports 2PC. > >> > b. Manage information of foreign prepared transactions resolver > >> > > >> > Masahiko Sawada will post the patch. > >> > > >> > > >> > > > > Thanks Vinayak and Sawada-san for taking this forward and basing your > work > > on my patch. > > > >> > >> Still lot of work to do but attached latest patches. > >> These are based on the patch Ashutosh posted before, I revised it and > >> divided into two patches. > >> Compare with original patch, patch of pg_fdw_xact_resolver and > >> documentation are lacked. > > > > > > I am not able to understand the last statement. > > Sorry to confuse you. > > > Do you mean to say that your patches do not have pg_fdw_xact_resolver() > and > > documentation that my patches had? > > Yes. > I'm confirming them that your patches had. > Thanks for the clarification. I had added pg_fdw_xact_resolver() to resolve any transactions which can not be resolved immediately after they were prepared. There was a comment from Kevin (IIRC) that leaving transactions unresolved on the foreign server keeps the resources locked on those servers. That's not a very good situation. And nobody but the initiating server can resolve those. That functionality is important to make it a complete 2PC solution. So, please consider it to be included in your first set of patches. -- Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company
