Re: Should use MERGE use BulkInsertState ?

On 2022-May-11, Justin Pryzby wrote:

> Should it use it ?
>
> It occured to me to ask when reading Bruce's release notes, which say:
> | [MERGE] is similar to INSERT ... ON CONFLICT but more batch-oriented.
>
> Currently, INSERT *never* uses bistate - even INSERT SELECT.
>
> INSERTing 10k tuples will dirty 10k buffers - not limited to the size of a
> strategy/ring buffer. Currently, MERGE will do the same.

As I understand it, the point of using a ring is to throttle performance
for bulk operations such as vacuum. I'm not sure why we would want to
throttle either MERGE or INSERT; it seems to me that we should want them
to go as fast as possible.

If MERGE were to use a ring buffer, why wouldn't UPDATE do the same?
There are some comments to that effect in src/backend/buffer/README --
they do mention UPDATE/DELETE and not INSERT. It seems to me that these
three commands (MERGE/UPDATE/DELETE) should be handled in similar ways,
so I don't think we need to consider lack of MERGE using a ring buffer
an open item for pg15.

COPY uses a ring buffer too.

--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/