On Mon, Feb 3, 2020 at 9:51 AM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Fri, Jan 10, 2020 at 10:53 AM Dilip Kumar <dilipbal...@gmail.com> wrote: > > > > On Mon, Dec 30, 2019 at 3:43 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > > > > > > > 2. During commit time in DecodeCommit we check whether we need to skip > > > > the changes of the transaction or not by calling > > > > SnapBuildXactNeedsSkip but since now we support streaming so it's > > > > possible that before we decode the commit WAL, we might have already > > > > sent the changes to the output plugin even though we could have > > > > skipped those changes. So my question is instead of checking at the > > > > commit time can't we check before adding to ReorderBuffer itself > > > > > > > > > > I think if we can do that then the same will be true for current code > > > irrespective of this patch. I think it is possible that we can't take > > > that decision while decoding because we haven't assembled a consistent > > > snapshot yet. I think we might be able to do that while we try to > > > stream the changes. I think we need to take care of all the > > > conditions during streaming (when the logical_decoding_workmem limit > > > is reached) as we do in DecodeCommit. This needs a bit more study. > > > > I have analyzed this further and I think we can not decide all the > > conditions even while streaming. Because IMHO once we get the > > SNAPBUILD_FULL_SNAPSHOT we can add the changes to the reorder buffer > > so that if we get the commit of the transaction after we reach to the > > SNAPBUILD_CONSISTENT. However, if we get the commit before we reach > > to SNAPBUILD_CONSISTENT then we need to ignore this transaction. Now, > > even if we have SNAPBUILD_FULL_SNAPSHOT we can stream the changes > > which might get dropped later but that we can not decide while > > streaming. > > > > This makes sense to me, but we should add a comment for the same when > we are streaming to say we can't skip similar to how we do during > commit time because of the above reason described by you. Also, what > about other conditions where we can skip the transaction, basically > cases like (a) when the transaction happened in another database, (b) > when the output plugin is not interested in the origin and (c) when we > are doing fast-forwarding I will analyze those and fix in my next version of the patch.
-- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
