Re: POC: postgres_fdw insert batching

On Tue, Jun 30, 2020 at 1:22 PM Ashutosh Bapat
<ashutosh.bapat@2ndquadrant.com> wrote:
> On Tue, 30 Jun 2020 at 08:47, Etsuro Fujita <etsuro.fujita@gmail.com> wrote:
>> On Mon, Jun 29, 2020 at 7:52 PM Ashutosh Bapat
>> <ashutosh.bapat.oss@gmail.com> wrote:
>> > On Sun, Jun 28, 2020 at 8:40 PM Tomas Vondra
>> > <tomas.vondra@2ndquadrant.com> wrote:
>>
>> > > 3) What about the other DML operations (DELETE/UPDATE)?
>> > >
>> > > The other DML operations could probably benefit from the batching too.
>> > > INSERT was good enough for a PoC, but having batching only for INSERT
>> > > seems somewhat asmymetric. DELETE/UPDATE seem more complicated because
>> > > of quals, but likely doable.
>> >
>> > Bulk INSERTs are more common in a sharded environment because of data
>> > load in say OLAP systems. Bulk update/delete are rare, although not
>> > that rare. So if an approach just supports bulk insert and not bulk
>> > UPDATE/DELETE that will address a large number of usecases IMO. But if
>> > we can make everything work together that would be good as well.
>>
>> In most cases, I think the entire UPDATE/DELETE operations would be
>> pushed down to the remote side by DirectModify.  So, I'm not sure we
>> really need the bulk UPDATE/DELETE.
> That may not be true for a partitioned table whose partitions are foreign tables. Esp. given the work that Amit
Langoteis doing [1]. It really depends on the ability of postgres_fdw to detect that the DML modifying each of the
partitionscan be pushed down. That may not come easily. 

While it's true that how to accommodate the DirectModify API in the
new inherited update/delete planning approach is an open question on
that thread, I would eventually like to find an answer to that.  That
is, that work shouldn't result in losing the foreign partition's
ability to use DirectModify API to optimize updates/deletes.

--
Amit Langote
EnterpriseDB: http://www.enterprisedb.com