Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

On Tue, Jun 23, 2020 at 10:13 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Jun 23, 2020 at 8:18 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Mon, Jun 22, 2020 at 6:38 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > >
> > > On Mon, Jun 22, 2020 at 5:26 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > >
> > > > > > @@ -2012,8 +2014,6 @@ ReorderBufferForget(ReorderBuffer *rb,
> > > > > > TransactionId xid, XLogRecPtr lsn)
> > > > > > if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
> > > > > > ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
> > > > > > txn->invalidations);
> > > > > > - else
> > > > > > - Assert(txn->ninvalidations == 0);
> > > > > >
> > > > > > Why this Assert is removed?
> > > > >
> > > > > Even if the base_snapshot is NULL, now we are collecting the
> > > > > txn->invalidation.
> > > > >
> > > >
> > > > But there doesn't seem to be any check even before this patch which
> > > > directly prohibits accumulating invalidations in DecodeCommit. We
> > > > have check for base_snapshot in ReorderBufferCommit. Did you get any
> > > > failure with that check?
> > >
> > > Because earlier ReorderBufferForget for toptxn will be called if the
> > > top transaction is aborted and in abort case, we are not logging any
> > > invalidation so that will be 0. However same is not true now.
> > >
> >
> > AFAICS, ReorderBufferForget() is called (via DecodeCommit) only when
> > we need to skip the transaction. It doesn't seem to be called from
> > Abort path (DecodeAbort/ReorderBufferAbort doesn't use
> > ReorderBufferForget). I am not sure which code path are you referring
> > here, can you please share the code flow which you are referring to
> > here.
>
> I think you are right, during some intermediate code change, it
> crashed on that assert (I guess I might be adding invalidation to the
> sub-transaction but not sure what was that state) and I assumed that
> is the reason that I explained above but, now I see my assumption was
> wrong. I will put back that assert. By testing, I could not hit any
> case where we hit that assert even after my changes, still I will put
> more thought if by any chance our case is different then the base
> code.

Here is the POC patch to discuss the idea of a cleanup of shared
fileset on proc exit. As discussed offlist, here I am maintaining
the list of shared fileset. First time when the list is NULL I am
registering the cleanup function with on_proc_exit routine. After
that for subsequent fileset, I am just appending it to filesetlist.
There is also an interface to unregister the shared file set from the
cleanup list and that is done by the caller whenever we are deleting
the shared fileset manually. While explaining it here, I think there
could be one issue if we delete all the element from the list will
become NULL and on next SharedFileSetInit we will again register the
function. Maybe that is not a problem but we can avoid registering
multiple times by using some flag in the file

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com