Fix stale fieldsCache in withPgDebug across AtOnce queries#803
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LaurentRDC merged 1 commit intohaskell-beam:masterfrom Apr 23, 2026
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…eam#802) renderExecReturningList called cachedGetFields but then freed the result via unsafeFreeResult, allowing libpq to reuse the pointer address on the next Pg.exec. A subsequent query with different column types would get a false cache hit and inherit stale field OID metadata, causing a BeamRowReadError on column 0. Fix: renderExecReturningList calls getFields directly. The cache remains for stepProcess (CursorBatching), where it is safe and beneficial. Regression test added to beam-postgres-tests. Fixes haskell-beam#802, regression introduced in haskell-beam#797. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Ooof, thanks for sending a patch. This is very unfortunate |
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beam-postgres-0.5.6.0 has been deprecated in Hackage. I'm preparing release 0.5.6.1 which will include this fix. It will be released tomorrow |
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Thank you! |
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Summary
renderExecReturningList(theAtOncepath) was callingcachedGetFieldsand then freeing the result viaPg.unsafeFreeResult. libpq can reuse the freed pointer address on the nextPg.exec, causing the next query to get a false cache hit and inherit stale field OID metadata from the previous query.renderExecReturningListnow callsgetFieldsdirectly. ThecachedGetFieldsone-entry cache is preserved forstepProcess(CursorBatching), whereunsafeFreeResultis never called and the cache is both safe and beneficial (avoidsgetFieldsper row within a 256-row batch).TEXTvsINT4) queried in sequence within onerunBeamPostgrescall.Fixes #802. Regression introduced in #797.
Test plan
cabal test beam-postgres-tests --test-options="--pattern fieldsCache"passescabal test beam-postgres-testspasses🤖 Generated with Claude Code