Postgres Source (Rust)

Rust port of the Python postgres_source example.

It reads product rows from a Postgres source table, computes a derived field (total_value = price × amount) and a text embedding per row, and writes the result into another Postgres table (with a pgvector index) using CocoIndex's declarative TableTarget. Then it serves pgvector similarity search over the output.

Parallel to the Python example

Concern	Python	Rust (this example)
Source rows	`postgres.PgTableSource(...).fetch_rows()`	`postgres::read_table::<SourceProduct>(db, "source_products")`
Per-row compute	`@coco.fn(memo=True) process_product`	`#[cocoindex::function(memo)] process_product`
Output store	`postgres.TableTarget` + vector index	`postgres::mount_table_target` + `declare_vector_index`
Embeddings	`sentence-transformers/all-MiniLM-L6-v2`	`fastembed` `AllMiniLML6V2` (same model, 384-dim)

Incrementality

Unchanged source rows are memo-skipped — no re-embedding on re-runs.
Changed source rows are reprocessed, and their output rows updated.
Source rows that are deleted have their derived output rows reconciled away automatically (the managed TableTarget deletes the orphaned row).

Run

Start a Postgres with pgvector and point POSTGRES_URL at it:

bash

export POSTGRES_URL="postgres://cocoindex:cocoindex@localhost/cocoindex"
export SOURCE_DATABASE_URL="$POSTGRES_URL"  # optional; defaults to POSTGRES_URL

# 1. Create + seed the source table
psql "$SOURCE_DATABASE_URL" -f prepare_source_data.sql

# 2. Read source -> embed -> write output table (incremental on re-run)
cargo run -- index

# 3. Semantic search over the output
cargo run -- query "wireless headphones"

Re-run cargo run -- index after UPDATE/DELETE/INSERT on source_products to see incremental reprocessing.