Memory not released in DuckDB-WASM after query execution

[frosshirt]

What happens?

In DuckDB-WASM, memory usage remains high after executing a query and is not released, even after performing additional operations. This is particularly noticeable when running queries on an entire table (e.g., calculating a hash across the table or performing SELECT *). Memory usage stays elevated regardless of subsequent actions.

This behavior can be reproduced with generated data and appears to affect only DuckDB-WASM, not the CLI on Windows or Linux. The issue is also reproducible in the latest version (1.1.2) on shell.duckdb.org.

After select:

To Reproduce

Example SQL to reproduce:

CREATE TABLE t AS SELECT random() AS value FROM range(1, 10000000);
SELECT hash(string_agg(t::text)) FROM t;

Memory remains high (~2 GB) until DuckDB-WASM is completely terminated.

Running similar queries with new random data does not increase memory usage further. It seems that DuckDB frees the memory, but the WASM worker does not.

Browser/Environment:

Chrome 130 and Firefox (22524)

Device:

Windows

DuckDB-Wasm Version:

1.29.1

DuckDB-Wasm Deployment:

shell.duckdb.org

Full Name:

Fabian Roßhirt

Affiliation:

IBIS Prof. Thome AG