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

On Mon, May 18, 2020 at 5:57 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Mon, May 18, 2020 at 4:10 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Sun, May 17, 2020 at 12:41 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > >
>
> Few comments on v20-0010-Bugfix-handling-of-incomplete-toast-tuple
> 1.
> + /*
> + * If this is a toast insert then set the corresponding bit. Otherwise, if
> + * we have toast insert bit set and this is insert/update then clear the
> + * bit.
> + */
> + if (toast_insert)
> + toptxn->txn_flags |= RBTXN_HAS_TOAST_INSERT;
> + else if (rbtxn_has_toast_insert(txn) &&
> + ChangeIsInsertOrUpdate(change->action))
> + {
>
> Here, it might better to add a comment on why we expect only
> Insert/Update? Also, it might be better that we add an assert for
> other operations.

I have added comments that why on Insert/Update we clean the flag.
But I don't think we only expect insert/update, we might get the
toast delete right? because in toast update we will do toast delete +
toast insert. So when we get toast delete we just don't want to do
anything.

>
> 2.
> @@ -1865,8 +1920,8 @@ ReorderBufferProcessTXN(ReorderBuffer *rb,
> ReorderBufferTXN *txn,
> * disk.
> */
> dlist_delete(&change->node);
> - ReorderBufferToastAppendChunk(rb, txn, relation,
> - change);
> + ReorderBufferToastAppendChunk(rb, txn, relation,
> + change);
> }
>
> This seems to be a spurious change.

Done

> 3.
> + /*
> + * If streaming is enable and we have serialized this transaction because
> + * it had incomplete tuple. So if now we have got the complete tuple we
> + * can stream it.
> + */
> + if (ReorderBufferCanStream(rb) && can_stream && rbtxn_is_serialized(toptxn)
> + && !(rbtxn_has_toast_insert(txn)) && !(rbtxn_has_spec_insert(txn)))
> + {
>
> This comment is just saying what you are doing in the if-check. I
> think you need to explain the rationale behind it. I don't like the
> variable name 'can_stream' because it matches ReorderBufferCanStream
> whereas it is for a different purpose, how about naming it as
> 'change_complete' or something like that. The check has many
> conditions, can we move it to a separate function to make the code
> here look clean?

As per the other comments we have removed this part in the latest patch set.

Apart from these comments fixes, there are 2 more changes
1. Handling of the toast tuple is changed as per the offlist
discussion with you
Basically, now, instead of not streaming the txn with the incomplete
tuple, we are streaming it up to the last complete lsn. So of the txn
has incomplete changes but its complete size is largest then we will
stream this. And, after streaming we will truncate the transaction up
to the last complete lsn.

2. There is a bug fix in handling the stream abort in 0008 (earlier it
was 0006).

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