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A Discord Question Exposed Two RAG Bugs—and Fixing Them Found a Third

A Discord question about documents and memories led Ankit Verma to uncover citation, memory-recency, and Kafka sink delete bugs—and tests that shared the code’s blind spots.
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A precise question about how retrieved documents and stored memories relate led Ankit Verma to find two bugs in his RAG system—and a third while building its Kafka Connect sink. The failures involved misleading source citations, memory recency, and a delete error that retries concealed. Verma’s account is a useful case study in how assumptions shared by code and tests can let defects survive.

Verma published his account on September 13, 2026. The implementation details and test results below are his reports about Ossian, not independently verified findings. His opening observation captures the central lesson: “Every test passed. The tests had the same blind spots as the code.”

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How can several retrieved chunks misrepresent the evidence?

Retrieval returned chunks, but Ossian presented the top six chunks to the model as numbered sources. In Verma’s example, three passages from engineering-handbook.txt appeared as citations [1], [2], and [3], alongside a passage from platform-architecture.md. A reader could mistake three passages from one document for agreement among three independent sources.

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Ingest-time content-hash deduplication did not solve this: the passages were distinct chunks in the same legitimate document, not duplicate content. The mismatch was between the unit retrieval returned (a chunk) and the unit the citation was supposed to represent (a document).

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Group by document before numbering citations

Verma’s reported fix groups retrieved chunks by document ID before constructing the prompt. Passages from the same document stay together under one citation number, and the document is ranked by its best chunk. Grouping by ID, rather than filename, also keeps separate documents with identical filenames distinct.

In one live question, Verma reports that six retrieved chunks became five citations, with a runbook contributing two passages under one citation. That is an example from one question, not a general performance measure.

Why did a repeated memory keep getting older?

Ossian ranked a memory with the formula similarity × importance × 0.5^(age / 30 days). The query calculated age from created_at. When a restatement matched an existing memory, a deduplicating upsert changed updated_at, but the ranking still used the original creation time. A preference could therefore keep losing recency weight even after being stated again.

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Distinguish when a memory was created, stated, and recalled

These timestamps answer different questions. Creation records when the memory first entered storage. A statement timestamp records when the person last said the fact. A recall or last-used timestamp records when the system accessed it. If the goal is to make a restated fact feel recent, the ranking needs the last-stated time—not simply creation or recall time.

Verma considered refreshing last_used_at whenever a memory was recalled, but rejected that approach: if older and newer contradictory memories are both recalled, refreshing both can make them tie on recency. His reported change instead measures age from the last time the fact was stated.

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Verma gives project-specific score examples from the running system: a fresh “switched the editor to the light theme” memory scored 0.765; “prefers the dark theme” scored 0.102 when it was 90 days old; and after the dark-theme preference was restated, it scored 0.817. These are reported system examples, not portable benchmarks.

What did fixing the first two bugs leave unresolved?

The Discord question asked how to handle conflicts between retrieved documents and stored memories, and how to handle multiple pieces of context that come from the same underlying source. Verma says the system does not fully answer it. Documents and memories remain separate; memories have no link back to the document from which they were learned, and semantically similar or contradictory memories are not reconciled.

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Grouping chunks by document improves citation accuracy, but it does not establish the provenance of a stored memory or decide which conflicting fact should win. Those require separate links and conflict-handling behavior; Verma’s account does not describe a completed solution for them.

How did a delete fail once and then succeed on retry?

While building a Kafka Connect sink for a Debezium-fed corpus, Verma found an ordering problem. The sink handled a DELETE by removing the document and then recording an ingest event with the deleted document_id. A foreign-key constraint rejected the event row. Because the batch loop did not catch that error, every event in the batch failed.

The retry followed a different state: the document was already gone, so there was nothing left to delete, and the event was recorded with a null document ID. The retry succeeded, concealing the first-attempt failure. Verma says this happened once per document.

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“insert or update on table "ingest_events" violates foreign key constraint Key (document_id)=(…) is not present in table "documents".”

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The ellipsis is a redaction in the quoted error. The important diagnostic is the sequence: the first attempt changed state before failing, so retrying did not repeat the same path. A successful retry alone did not show that the original operation was clean.

What design choices did the sink use?

Verma says the sink uses a stable caller-supplied event ID because the event API is idempotent on that ID. The ID combines connector name, topic, partition, and offset with the record timestamp. He rejected using Debezium’s source position alone: according to his account, rows in an initial snapshot share one LSN, so relying on that value alone could make distinct rows collide and later rows be discarded as duplicates.

  • Blanked rows are removed so stale text does not remain in the corpus.
  • Records with none of the configured text fields are rejected as a likely configuration error, and Debezium placeholder values are refused.
  • Synchronous put() keeps offsets from advancing ahead of delivery.
  • Rate limits and 5xx responses trigger backoff using Retry-After; rejected records go to a dead-letter queue; a 401 stops the task.

These are design details reported by Verma, not independent review findings.

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What did the reported end-to-end checks cover?

Verma reports running the sink against a Postgres table and checking these cases:

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  • A three-row snapshot produced three answerable documents.
  • Updating a value from 180 to 90 days changed the answer without leaving an old chunk that still said 180.
  • A delete removed the document and its chunks.
  • A blanked row disappeared.
  • Resetting sink offsets replayed 18 events before and after without adding documents.

The 18-before, 18-after figure is an author-reported replay check, not a benchmark. The checks cover useful state transitions, but they do not independently establish how the sink behaves across other databases, deployments, or failure conditions.

Why did the tests miss the memory bug?

The recency test backdated created_at—the same field the faulty ranking query read. It verified that age affected ranking, but shared the implementation’s assumption that creation time represented recency. Verma says a new test fails against the old query and that he checked this by restoring the old line. At the time of the sink bug, he says, there were no tests for the event API.

A more discriminating test should give creation, last-stated, and last-used times different values, then assert that the ranking follows the intended one. For the delete path, test the event API at the state boundary where the foreign key can fail, and inspect the first attempt as well as the retry. A retry that succeeds can otherwise hide an error that happens only after state has changed.

Verma describes the value of explaining the system to someone who asks a precise question: “The fastest way I know to find that kind of bug is to explain the system to someone who asks a precise question — and check the code before you hit send.”

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Verma credits work with Claude (Anthropic), says numbers and code samples were checked against the running system, and says the piece was reviewed and published by @dockndevai. Those are the author’s disclosures. Read Verma’s original DEV Community account.

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