jemalloc

The jemalloc extension replaces the system’s memory allocator with jemalloc. jemalloc extension is statically linked and cannot be installed or loaded during runtime.

For thechnical reasons, we used to distribute jemalloc as an extension. Since DuckDB v1.5.3, it is distributred as a third-party library.

Operating System Support

The availability of the jemalloc extension depends on the operating system.

Linux

Linux distributions of DuckDB ship with the jemalloc by default. To disable jemalloc, build DuckDB from source and set the SKIP_EXTENSIONS flag as follows:

GEN=ninja SKIP_EXTENSIONS="jemalloc" make

macOS

The macOS version of DuckDB does with jemalloc but can be built from source to include it:

GEN=ninja BUILD_JEMALLOC=1 make

Windows

On Windows, this extension is not available.

Configuration

Environment Variables

The jemalloc allocator in DuckDB can be configured via the DUCKDB_JE_MALLOC_CONF environment variable. Setting this is equivalent to setting the MALLOC_CONF environment variable for jemalloc but DuckDB uses a different environment variable name to avoid potential name clashes with other applications.

Background Threads

By default, jemalloc’s background threads are disabled. To enable them, use the following configuration option:

SET allocator_background_threads = true;

Background threads asynchronously purge outstanding allocations so that this doesn’t have to be done synchronously by the foreground threads. This improves allocation performance, and should be noticeable in allocation-heavy workloads, especially on many-core CPUs.