[sgrebnov]

What

rows_to_arrow for MySQL cloned every cell (Row::get_opt clones the Value out of a borrowed row) and cloned the column name for every cell to use as error context. This change:

• takes Vec<Row> and moves each value out with Row::take_opt;
• borrows the column name instead of cloning it;
• fills columns one at a time.

The only caller, MySQLConnection::query_arrow, already owns the rows. Output is unchanged.

Measurements

rows_to_arrow on 800,000 synthetic rows (200 chunks of 4,000): 12 columns including five char(34), a varchar, two text/longtext columns (one with a 3,300-byte value), a tinyint and two timestamps. Allocations were counted with a counting global allocator, and are identical across runs. CPU time is three alternating runs per build on a loaded machine.

	before	after
heap allocations per row	20.06	0.06
bytes allocated per row	11,234	7,587
CPU per 4,000-row chunk (min)	3.73–3.83 ms	1.89–2.00 ms
CPU per 4,000-row chunk (p99)	4.30–4.52 ms	2.33–3.54 ms

The remaining per-cell allocation is mysql_common decoding each value into Value::Bytes, which this change does not touch.

Testing

• cargo test --features mysql --lib mysql: 5 passed.
• cargo test --features mysql --test integration mysql: 11 passed, 3 ignored, 1 failed (test_mysql_arrow_oneway). That test fails the same way on the base commit and is unrelated to this change.
• To run the integration tests locally, set CONTAINER_REGISTRY with a trailing slash. The default public.ecr.aws/docker/library resolves to .../librarymysql:latest.

[Copilot]

🟢 Approved

The ownership and iteration changes are straightforward, with no blocking correctness issues identified.

No open issues 🎉

What changed in this PR

Reduces allocations in MySQL-to-Arrow conversion by moving cell values rather than cloning them.

Changes:

• Consumes owned rows and converts values one column at a time.
• Borrows column names, allocating error context only when needed.
• Updates the query caller to transfer row ownership.

File	Description
core/​src/​sql/​db_connection_pool/​dbconnection/​mysqlconn.rs	Passes owned rows to the converter.
core/​src/​sql/​arrow_sql_gen/​mysql.rs	Moves cell values and avoids repeated column-name clones.

_{Review effort: Balanced}