Deprecate jemalloc recommendation in default Dockerfile and deployment guide (jemalloc development is dead)

ybiquitous · November 27, 2025, 6:48am

Hi,

As of June 2025, the original maintainer of jemalloc released an official post stating that the project is no longer maintained (postmortem). This brings security and stability risks for new Rails apps, which currently recommend and enable jemalloc by default. Refer to the guide below:

github.com/rails/rails

guides/source/tuning_performance_for_deployment.md?plain=1

65c8139a6


      
          To alleviate this problem, it is highly recommended to configure Ruby to use an alternative memory allocator:
          [jemalloc](https://github.com/jemalloc/jemalloc).

Also, Dockerfile generated by rails new contains jemalloc:

github.com/rails/rails

railties/lib/rails/generators/rails/app/templates/Dockerfile.tt

65c8139a6


      
          RUN apt-get update -qq && \
              apt-get install --no-install-recommends -y <%= dockerfile_base_packages.join(" ") %> && \
              ln -s /usr/lib/$(uname -m)-linux-gnu/libjemalloc.so.2 /usr/local/lib/libjemalloc.so && \
              rm -rf /var/lib/apt/lists /var/cache/apt/archives
          
          # Set production environment variables and enable jemalloc for reduced memory usage and latency.
          ENV RAILS_ENV="production" \
              BUNDLE_DEPLOYMENT="1" \
              BUNDLE_PATH="/usr/local/bundle" \
              BUNDLE_WITHOUT="development" \
              LD_PRELOAD="/usr/local/lib/libjemalloc.so"
          
          # Throw-away build stage to reduce size of final image
          FROM base AS build
          
          # Install packages needed to build gems<%= (using_node? || using_bun?) ? " and node modules" : "" %>
          RUN apt-get update -qq && \
              apt-get install --no-install-recommends -y <%= dockerfile_build_packages.join(" ") %> && \
              rm -rf /var/lib/apt/lists /var/cache/apt/archives
          
          <% if using_node? -%>

Given jemalloc’s current status, should we deprecate or remove its installation and recommendation from the official templates and docs? Or at the very least, add a prominent warning?

Would appreciate thoughts and feedback.

Thanks.

See also Feature #14718: Use jemalloc by default? - Ruby - Ruby Issue Tracking System , where it was discussed whether Ruby should use jemalloc by default. It’s now closed, though.

dreamofcode321go · December 3, 2025, 3:59am

Is there an alternative library?

ybiquitous · December 4, 2025, 4:45am

I’m not so familiar with this area, but I quickly found the other memory allocators below:

GitHub - microsoft/mimalloc: mimalloc is a compact general purpose allocator with excellent performance.
GitHub - google/tcmalloc
GitHub - mjansson/rpmalloc: Public domain cross platform lock free thread caching 16-byte aligned memory allocator implemented in C

However, I’ve never tried them, and there may be other allocators I’m unaware of.

It’d be helpful if anyone could provide any information here.

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Deprecate jemalloc recommendation in default Dockerfile and deployment guide (jemalloc development is dead)

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