From: Daniel Frey <d.frey@gmx.de>
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Subject: Pipeline Mode vs Single Row Mode / Chunked Rows Mode
Message-Id: <A86C45C5-4E99-49B8-93E0-EEDC3DA4235B@gmx.de>
Date: Thu, 19 Dec 2024 15:36:49 +0100
To: pgsql-general <pgsql-general@lists.postgresql.org>
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Precedence: bulk

Hi,

I'm adding support for Pipeline Mode to my C++ PostgreSQL client library =
(https://github.com/taocpp/taopq) and I tried to understand the =
interaction between Pipeline Mode and Single Row Mode / Chunked Rows =
Mode. It seems that it works sometimes, but I don't get the feeling that =
it was deliberately designed to work consistently. Example:

* Consider a table with three rows of data
* I send two (identical) SELECT commands, e.g. "SELECT * FROM =
test_table"
* I call PQpipelineSync()
* I call PQsetSingleRowMode()
* I read the results, I get
  * One result with size 1
  * Another one with size 1
  * Another one with size 1
  * A final one with size 0 for the first select
  * A result with size 3 for the second select
  * A result with PGRES_PIPELINE_SYNC

When I try to call PQsetSingleRowMode() for the second SELECT, it fails.
It also seems weird that I can call it for the first result after the =
sync call, but maybe that's OK?

Anyway, is there some documentation about how these modes interact and =
how they can be combined? Or should they never be combined?

-Daniel