[jkaczman]

#1988, the previous PR implementing unnest split, only handled splitting when the SELECT for the INSERT was SELECT *, e.g., in INSERT INTO <sharded table> .. SELECT * FROM unnest($1, ..). As this is unimplemented functionality, since #1987, we (correctly) returned an error for this, as this is one of the cases not handled by that previous PR (anything other than SELECT *).

Now, as an extension of #1988, this PR also splits these unnest INSERTs when the SELECT explicitly lists the output columns of unnest(..) one at a time instead of *, as well as when the SELECT includes constants (e.g., NULL).

The motivation for this is fully completing unnest support (instead of VALUES) for re-writing subqueries.

E.g., if we have a statement such as

INSERT INTO subpackages (id, user_id, order_id) SELECT id, id + 1, NULL FROM suborders

The subquery support I'm working on for unnest will run SELECT id, id + 1, NULL FROM suborders on the shards. The shards return some rows, e.g., (1, 2, NULL), (2, 3, NULL) and (3, 4, NULL). Then, subqueries will send these rows back to the INSERT as unnest(..) arrays. However, the shards return the NULL column with the type text (default Postgres association for the NULL constant). If we sent the NULL column as an array too, the array would be a text[], and Postgres would return an error when we insert text into the bigint column order_id. Not to mention, this is inefficient. Therefore, I opted when implementing support for this in subqueries to keep the constants in the SELECT as a nice workaround:

INSERT INTO subpackages (id, user_id, order_id) SELECT u.c1, u.c2, NULL FROM unnest($1::pg_catalog._int8, $2::pg_catalog._int8) AS u(c1, c2)

SELECT * would only return the columns of unnest(..), so there'd be no way for SELECT to include the NULL with SELECT * without the array mentioned prior. Therefore, we need this PR before subquery support can use unnest(..) to properly split constants apart from the unnest array.

To route the rows, this follows the alias AS u(c1, c2) and the SELECT to find the unnest(..) argument that Postgres uses to insert into the sharding key. Then, the rows are routed as if the client sent INSERT INTO subpackages (id, user_id, order_id) VALUES ($1, $2, NULL).

[github-actions]

Metal bench (arm64) failed. build failed to run.

Logs

build, verdict.json

Ran 00d0ea1 on m8g.metal-24xl (spot).

[github-actions]

Metal bench (x86) failed. build failed to run.

Logs

build, verdict.json

Ran 00d0ea1 on c7i.metal-48xl (on-demand).

[codecov]

Codecov Report

❌ Patch coverage is 99.47368% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...frontend/router/parser/rewrite/statement/insert.rs	99.32%	1 Missing ⚠️

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