On supported platforms, DuckDB replaces the system's memory allocator with jemalloc. jemalloc is statically linked into DuckDB and cannot be installed or loaded during runtime.

For technical reasons, we used to distribute jemalloc as an extension. Since DuckDB 1.5.3, it is distributed as a third-party library.

Operating System Support

The availability of jemalloc depends on the operating system.

Linux

64-bit Linux distributions of DuckDB ship with jemalloc by default (with the exception of builds for musl-based distributions). To disable jemalloc, build DuckDB from source and set the BUILD_JEMALLOC flag to 0 as follows:

GEN=ninja BUILD_JEMALLOC=0 make

This flag is passed to CMake as -DENABLE_JEMALLOC=0.

macOS and Windows

On macOS and Windows, jemalloc is not available. DuckDB uses the system's memory allocator on these platforms.

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.