Dual Execution
When a query touches both lake-synced and Snowflake-only tables, melt’s router splits the plan: Snowflake-resident operators ship to Snowflake, the rest run in DuckDB, and Arrow batches stitch the result. No whole-query fallback, no SQL changes.
Dual Execution in three steps.
Parse and classify placement
The proxy parses incoming Snowflake-dialect SQL and walks every ObjectName.
Build the hybrid plan
The plan builder walks the AST and produces an Arc<HybridPlan> whose root: PlanNode tree carries Placement annotations and RemoteSql collapse nodes.
Choose a strategy per fragment
BridgeStrategy::Attach for single-scan nodes — run as sf_link.
Drop in. Same drivers. Lower bill.
No more all-or-nothing cliff
Without dual exec, one Snowflake-only table forces the entire query back to Snowflake — even if 90% of the bytes are lake-resident.
Sub-query level cost reduction
The router’s pushdown collapse rule turns multi-table remote subtrees into a single Snowflake-side join, executed natively.
Parity-checked correctness
Every hybrid query is eligible for replay against pure Snowflake at hybrid_parity_sample_rate.
Get up and running in 5 minutes.
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