Import duckdb-replicator

runtime/pkg/rduckdb/README.md

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+# rduckdb
+
+## Motivation
+1. As an embedded database, DuckDB does not inherently provide the same isolation for ETL and serving workloads that other OLAP databases offer.
+2. We have observed significant degradation in query performance during data ingestion.
+3. In a Kubernetes environment, it is recommended to use local disks instead of network disks, necessitating separate local disk backups.
+
+## Features
+1. Utilizes separate DuckDB handles for reading and writing, each with distinct CPU and memory resources.
+2. Automatically backs up writes to GCS in real-time.
+3. Automatically restores from backups when starting with an empty local disk.
+
+## Examples
+1. Refer to `examples/main.go` for a usage example.
+
+## Future Work
+1. Enable writes and reads to be executed on separate machines.
+2. Limit read operations to specific tables to support ephemeral tables (intermediate tables required only for writes).