storage: clear the oneshot-source decode arena per row#37135
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frankmcsherry merged 1 commit intoJun 18, 2026
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`render_decode_chunk` created a single `RowArena` in the operator body and reused it across every chunk and row without ever clearing it, so the MFP-evaluation temporaries for the entire source accumulated for the lifetime of the COPY — an unbounded arena. Scope the arena to each decoded chunk and clear it per row, so it holds at most one row's temporaries and is freed when the chunk is done. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
render_decode_chunk(the oneshot/COPY decode operator) created oneRowArenain the operator body and reused it across every chunk and every row without ever clearing it. The arena owns whatever is pushed into it for its lifetime, so the MFP-evaluation temporaries for the entire source accumulated until the COPY finished — an unbounded arena proportional to the data volume.This scopes the arena to each decoded chunk and clears it per row, so it holds at most one row's worth of temporaries and is released when the chunk is processed.
Why
Found while auditing
RowArenalifetimes (companion to the arena work in #37114 / #37134). This was the only arena in the audit that was both operator-lived and never cleared — i.e. a genuine unbounded accumulation rather than a bounded high-water. It brings the operator in line with the "arena per batch, cleared per row" idiom the other operators use.Tests
No behavior change (the MFP output is identical; only the arena's lifetime changes). Covered by the existing oneshot-source / COPY FROM tests.