On Mon, Oct 21, 2019 at 10:48 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Fri, Oct 18, 2019 at 5:32 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> > 3.
> > @@ -2479,7 +2480,7 @@ ReorderBufferSerializeTXN(ReorderBuffer *rb,
> > ReorderBufferTXN *txn)
> >
> > /* update the statistics */
> > rb->spillCount += 1;
> > - rb->spillTxns += txn->serialized ? 1 : 0;
> > + rb->spillTxns += txn->serialized ? 0 : 1;
> > rb->spillBytes += size;
> >
> > Why is this change required? Shouldn't we increase the spillTxns
> > count only when the txn is serialized?
>
> Prior to this change it was increasing the rb->spillTxns, every time
> we try to serialize the changes of the transaction. Now, only we
> increase first time when it is not yet serialized.
>
> >
> > 3.
> > ReorderBufferSerializeTXN()
> > {
> > ..
> > /* update the statistics */
> > rb->spillCount += 1;
> > rb->spillTxns += txn->serialized ? 0 : 1;
> > rb->spillBytes += size;
> >
> > Assert(spilled == txn->nentries_mem);
> > Assert(dlist_is_empty(&txn->changes));
> > txn->nentries_mem = 0;
> > txn->serialized = true;
> > ..
> > }
> >
> > I am not able to understand the above code. We are setting the
> > serialized parameter a few lines after we check it and increment the
> > spillTxns count. Can you please explain it?
>
> Basically, when the first time we attempt to serialize a transaction,
> txn->serialized will be false, that time we will increment the
> rb->spillTxns and after that set txn->serialized to true. From next
> time onwards if we try to serialize the same transaction we will not
> increment the rb->spillTxns so that we count each transaction only
> once.
>
Your explanation for both the above comments makes sense to me. Can
you please add some comments along these lines because it is not
apparent why one wants to increase the spillTxns counter when
txn->serialized is false?
> >
> > Also, isn't spillTxns count bit confusing, because in some cases it
> > will include subtransactions and other cases (where the largest picked
> > transaction is a subtransaction) it won't include it?
>
> I did not understand your comment completely. Basically, every
> transaction which we are serializing we will increase the count first
> time right? whether it is the main transaction or the sub-transaction.
>
It was not clear to me earlier whether we always increase the
spillTxns counter for subtransactions or not. But now, looking at
code carefully, it is clear that is it is getting increased in every
case. In short, you don't need to do anything for this comment.
--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com