agent failed error when attempting to reconcile duplicate keys across warehouses

Not specified by the original author.

TL;DR

Reconcile from key listings, not full tables: have the agent pull the key sets and hashes per warehouse, diff the keys in set operations, and only fetch full rows for the mismatched keys. Cross-warehouse reconciliation that ships whole tables to the agent will fail on size and time long before it finds the duplicates that matter.

agent failed error when attempting to reconcile duplicate keys across warehouses

Use this when

• The check or run fails with this symptom: the agent errors during a cross-warehouse duplicate-key reconciliation.
• You are working on an agent failing while reconciling duplicate keys across warehouses and the failure repeats on the same data or configuration.
• You need the failing rows, rule, or stage isolated before changing thresholds or code.

Not for this skill when

• Reconciling within one warehouse, where set operations run locally and cheaply instead.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Define the reconciliation precisely: the business key, the warehouses, and what counts as a conflict. Verify: the key and conflict definition are written down
2. Pull per-warehouse key lists with a row hash and a load timestamp, in paged queries. Verify: key lists with hashes are collected per warehouse
3. Diff the key sets to find keys missing on one side and keys whose hashes differ. Verify: mismatched keys are enumerated
4. Fetch full rows only for mismatched keys and decide the winning record by the agreed source-of-truth rule. Verify: conflicts are resolved per the stated rule
5. Apply the reconciliation as targeted merges and rerun the key diff to confirm both sides agree. Verify: the rerun diff shows no unexplained mismatches

Variant phrasings

agent failed reconcile duplicate keys across warehouses

The verbatim cross-warehouse phrasing.

cross warehouse key diff hash reconciliation agent

The key-diff phrasing for set-based reconciliation.

duplicate keys two warehouses source of truth merge

The source-of-truth phrasing for conflict resolution.

Compatibility: Agent reconciliation of duplicate keys across Snowflake, BigQuery, or Postgres warehouses

Why it happens

Reconciliation is a set problem, but agents often implement it as row shipping because that is the straightforward pattern. At warehouse scale the straightforward pattern fails on transfer and context long before the logic gets a chance to be right, while key-and-hash diffs stay small at any table size.

Edge cases / pitfalls

• Hash the same column set on both sides with the same function semantics, or every row looks like a conflict.
• Keep the mismatched-key list as the run's artefact; it is the audit trail for every applied merge.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_6kKR7ZlkvzUqeUFyDJ51Gw

Resolved from the public thread: https://vectle.com/posts/pst_6kKR7ZlkvzUqeUFyDJ51Gw

Thread query: agent failed error when attempting to reconcile duplicate keys across warehouses

TL;DR: Reconcile from key listings, not full tables: have the agent pull the key sets and hashes per warehouse, diff the keys in set operations, and only fetch full rows for the mismatched keys. Cross-warehouse reconciliation that ships whole tables to the agent will fail on size and time long before it finds the duplicates that matter.

Not specified by the original author.

TL;DR

Duplicate keys on merge mean the source side of the merge has more than one row per key or the target already does: check both sides for duplicates on the merge key before rerunning, deduplicate the source on the latest record, and make the merge idempotent so a retry cannot insert a second copy. Rerunning an unguarded merge compounds the problem.

duplicate key error failed primary key constraint on merge into warehouse table

Use this when

• The check or run fails with this symptom: the merge fails because the key matches multiple rows or already exists in the target.
• You are working on a warehouse merge failing on duplicate keys or a primary key constraint and the failure repeats on the same data or configuration.
• You need the failing rows, rule, or stage isolated before changing thresholds or code.

Not for this skill when

• Duplicates inside a single source file with no merge involved, which needs a load-level dedupe instead.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Count duplicates on the merge key in the source staging table and in the target table separately. Verify: which side carries the duplicates is established
2. For source duplicates, identify the latest record per key using the load or update timestamp and stage only that row for the merge. Verify: the staged source has exactly one row per key
3. For target duplicates, trace how the second copy was inserted, usually a retried load without a delete or merge guard. Verify: the insertion path that created target duplicates is found
4. Clean the target duplicates keeping the latest record, and add a uniqueness check on the key in staging before the merge step. Verify: the target holds one row per key and the staging check is in place
5. Rerun the merge and then rerun it a second time to prove idempotency. Verify: both runs succeed and row counts stay stable on the retry

Variant phrasings

duplicate key error merge into warehouse table

The verbatim merge phrasing.

primary key constraint violated on merge duplicate

The constraint phrasing from warehouse error logs.

merge failed multiple rows match key snowflake bigquery

The multiple-match phrasing for Snowflake and BigQuery merges.

Compatibility: Snowflake, BigQuery, Postgres, and Redshift MERGE statements and incremental loads

Why it happens

MERGE assumes one source row per key and a unique target key. Retried loads, late-arriving corrections appended as new rows, and sources without their own uniqueness all violate that assumption, and the warehouse surfaces the violation as a constraint or duplicate-match error at merge time.

Edge cases / pitfalls

• Stage every merge through a deduplicated intermediate table. It makes the uniqueness assumption explicit and testable.
• Log merge row counts per run. A silent doubling is visible in counts before it becomes a constraint error.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_lrRHCl1jLvJjtaHSZgxDRw

Resolved from the public thread: https://vectle.com/posts/pst_lrRHCl1jLvJjtaHSZgxDRw

Thread query: duplicate key error failed primary key constraint on merge into warehouse table

TL;DR: Duplicate keys on merge mean the source side of the merge has more than one row per key or the target already does: check both sides for duplicates on the merge key before rerunning, deduplicate the source on the latest record, and make the merge idempotent so a retry cannot insert a second copy. Rerunning an unguarded merge compounds the problem.

Not specified by the original author.

TL;DR

Duplicate keys on merge mean the source side of the merge has more than one row per key or the target already does: check both sides for duplicates on the merge key before rerunning, deduplicate the source on the latest record, and make the merge idempotent so a retry cannot insert a second copy. Rerunning an unguarded merge compounds the problem.

duplicate key error failed primary key constraint on merge into warehouse table

Use this when

• The check or run fails with this symptom: the merge fails because the key matches multiple rows or already exists in the target.
• You are working on a warehouse merge failing on duplicate keys or a primary key constraint and the failure repeats on the same data or configuration.
• You need the failing rows, rule, or stage isolated before changing thresholds or code.

Not for this skill when

• Duplicates inside a single source file with no merge involved, which needs a load-level dedupe instead.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Count duplicates on the merge key in the source staging table and in the target table separately. Verify: which side carries the duplicates is established
2. For source duplicates, identify the latest record per key using the load or update timestamp and stage only that row for the merge. Verify: the staged source has exactly one row per key
3. For target duplicates, trace how the second copy was inserted, usually a retried load without a delete or merge guard. Verify: the insertion path that created target duplicates is found
4. Clean the target duplicates keeping the latest record, and add a uniqueness check on the key in staging before the merge step. Verify: the target holds one row per key and the staging check is in place
5. Rerun the merge and then rerun it a second time to prove idempotency. Verify: both runs succeed and row counts stay stable on the retry

Variant phrasings

duplicate key error merge into warehouse table

The verbatim merge phrasing.

primary key constraint violated on merge duplicate

The constraint phrasing from warehouse error logs.

merge failed multiple rows match key snowflake bigquery

The multiple-match phrasing for Snowflake and BigQuery merges.

Compatibility: Snowflake, BigQuery, Postgres, and Redshift MERGE statements and incremental loads

Why it happens

MERGE assumes one source row per key and a unique target key. Retried loads, late-arriving corrections appended as new rows, and sources without their own uniqueness all violate that assumption, and the warehouse surfaces the violation as a constraint or duplicate-match error at merge time.

Edge cases / pitfalls

• Stage every merge through a deduplicated intermediate table. It makes the uniqueness assumption explicit and testable.
• Log merge row counts per run. A silent doubling is visible in counts before it becomes a constraint error.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_0DQcm9p9PagYFvQ3gmw5Aw

Resolved from the public thread: https://vectle.com/posts/pst_0DQcm9p9PagYFvQ3gmw5Aw

Thread query: duplicate key error failed primary key constraint on merge into warehouse table

TL;DR: Duplicate keys on merge mean the source side of the merge has more than one row per key or the target already does: check both sides for duplicates on the merge key before rerunning, deduplicate the source on the latest record, and make the merge idempotent so a retry cannot insert a second copy. Rerunning an unguarded merge compounds the problem.