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Consumers on postgres:NN-alpine can't switch to the Debian pgvector image without reindexing every text index (musl vs glibc collation). This builds pgvector into the same Alpine image instead. Verified on PG 16 and 17.
29 lines
1.3 KiB
Markdown
29 lines
1.3 KiB
Markdown
# Postgres on Alpine with pgvector
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For stacks that already run `postgres:NN-alpine` and want the `vector`
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extension for fastmcp-feedback embeddings.
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Why not switch to the `pgvector/pgvector` image: it's Debian (glibc), and the
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Alpine images use musl. The two C libraries sort text differently under
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locales such as `en_US.utf8`, so reusing an Alpine data directory under a
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Debian image changes the order of every text index. The indexes need a full
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`REINDEX` or they silently return wrong results. Building pgvector into the
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same Alpine image keeps the data directory's collation unchanged.
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```bash
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docker build --build-arg PG_MAJOR=16 -t postgres-pgvector:16-alpine .
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docker build --build-arg PG_MAJOR=17 -t postgres-pgvector:17-alpine .
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```
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Then point the stack's Postgres service at the new image (same major version
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as the existing data directory) and run `CREATE EXTENSION IF NOT EXISTS
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vector;` once, or let a migration do it.
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Tested 2026-09-30 with pgvector v0.8.6 on postgres:16-alpine and
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postgres:17-alpine: the extension loads, and an HNSW `vector_cosine_ops`
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index is used for `ORDER BY embedding <=> ...` queries.
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`with_llvm=no` skips the LLVM bitcode used for JIT inlining. The base images'
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Postgres was built with a clang version Alpine no longer ships, so the bitcode
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step fails; pgvector itself still builds with gcc and works normally.
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