The jemalloc extension replaces the system's memory allocator with jemalloc. Unlike other DuckDB extensions, the jemalloc extension is statically linked and cannot be installed or loaded during runtime.

Operating System Support

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

Linux

Linux distributions of DuckDB ships with the jemalloc extension. To disable the jemalloc extension, 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 not ship with the jemalloc extension 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.