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

On Wed, Aug 5, 2020 at 7:37 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Wed, Aug 5, 2020 at 6:25 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
>
> > Can we add a test for incomplete changes (probably with toast
> > insertion but we can do it for spec_insert case as well) in
> > ReorderBuffer such that it needs to first serialize the changes and
> > then stream it? I have manually verified such scenarios but it is
> > good to have the test for the same.
>
> I have added a new test for the same in the stream.sql file.
>

Thanks, I have slightly changed the test so that we can consume DDL
changes separately. I have made a number of other adjustments like
changing few more comments (to make them consistent with nearby
comments), removed unnecessary inclusion of header file, ran pgindent.
The next patch (v47-0001-Implement-streaming-mode-in-ReorderBuffer) in
this series looks good to me. I am planning to push it after one more
read-through unless you or anyone else has any comments on the same.
The patch I am talking about has the following functionality:

Implement streaming mode in ReorderBuffer. Instead of serializing the
transaction to disk after reaching the logical_decoding_work_mem limit
in memory, we consume the changes we have in memory and invoke stream
API methods added by commit 45fdc9738b. However, sometimes if we have
incomplete toast or speculative insert we spill to the disk because we
can't stream till we have the complete tuple. And, as soon as we get
the complete tuple we stream the transaction including the serialized
changes. Now that we can stream in-progress transactions, the
concurrent aborts may cause failures when the output plugin consults
catalogs (both system and user-defined). We handle such failures by
returning ERRCODE_TRANSACTION_ROLLBACK sqlerrcode from system table
scan APIs to the backend or WALSender decoding a specific uncommitted
transaction. The decoding logic on the receipt of such a sqlerrcode
aborts the decoding of the current transaction and continues with the
decoding of other transactions. We also provide a new option via SQL
APIs to fetch the changes being streamed.

This patch's functionality can be independently verified by SQL APIs

--
With Regards,
Amit Kapila.