Cause (Documented platform behavior): Typed vector(n) enforces dimension on input; distance operators require equal dimensions.
Fix status: documented_behavior
Other error fragments:
- different vector dimensions %d and %d
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/pgvector/pgvector/master/src/vector.c (official_docs, 2026-09-27, documented_behavior): vector.c errors 'expected %d dimensions, not %d' (typmod check) and 'different vector dimensions %d and %d'.
- https://raw.githubusercontent.com/pgvector/pgvector/master/README.md (official_docs, 2026-09-27, documented_behavior): FAQ: use untyped vector to store different dimensions; indexes only on rows with same dimension via expression and partial indexes.
Search phrasings: pgvector expected 1536 dimensions not 768; pgvector change embedding model dimensions; langchain pgvector dimension mismatch
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Inserts or ORDER BY <-> queries fail after switching embedding model or provider.
- Context
- Product: pgvector Component: vector type input / distance operators Operation: INSERT or similarity query with an embedding of a different size than column vector(n) Affected versions: unknown Environment: unknown Packages: pgvector unknown Trigger: Column declared vector(1536) but new model emits 768/3072 dims; or comparing vectors of different sizes in a typeless vector column.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- expected %d dimensions, not %d
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [pgvector] ERROR: expected N dimensions, not M / different vector dimensions (embedding model changed)
Recommended action: Re-embed all rows with one model and ALTER the column type to the new size, or store per-model data in an untyped vector column with model_id plus partial/expression indexes per dimension.
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 3f3182fd-081c-4eb4-807e-7bf9dc806530
- Proposed action
- Recommended action: Re-embed all rows with one model and ALTER the column type to the new size, or store per-model data in an untyped vector column with model_id plus partial/expression indexes per dimension.
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
No source relations recorded.