_README.md

mamba 2.6 performance test

this is a replication of the repo2docker tests/conda/downgrade test (environment files are unmodified), which is dramatically slower after upgrading mamba to 2.6.

Two stages:

1. install initial frozen environment (@explicit file, no solve):

   mamba install -p /tmp/env -f environment.py-3.9-linux-64.lock
   

2. 'update' the env with packages that will force a downgrade:

   mamba env update -p /tmp/env -f downgrade.yml
   

With mamba 2.5.0, resolving and executing the downgrade takes ~85 seconds (42 seconds with a warm cache). With mamba 2.6.0, it takes 472 seconds (closer to 430 with warm cache).

This may not be a 100% perfect comparison with cache states, but ~all of the slowdown is in the mamba 2.6 Resolving environment step (424s), so cache shouldn't be super relevant.

Full script:

docker run --rm -it -v$PWD:/io -w /io --platform linux/amd64 quay.io/condaforge/miniforge3

# in container

# install mamba
mamba create -n mamba25 mamba=2.5
mamba create -n mamba26 mamba=2.6

# create base env
time mamba run -n mamba25 mamba create -y -p /tmp/test25 -f environment.py-3.9-linux-64.lock
time mamba run -n mamba26 mamba create -y -p /tmp/test26 -f environment.py-3.9-linux-64.lock

# run downgrade
time mamba run -n mamba25 mamba env update -y -p /tmp/test25 -f downgrade.yml
time mamba run -n mamba26 mamba env update -y -p /tmp/test26 -f downgrade.yml

downgrade.yml

# originally xeus-cling@0.6.0
# added python=3.9 pin because implicit downgrade of Python from 3.10 to 3.9 isn't allowed
name: xeus-cling
channels:
  - conda-forge
dependencies:
  - python=3.9
  - xeus-cling=0.6.0
  - xtensor=0.20.8
  - xtensor-blas=0.16.1
  - notebook

environment.py-3.9-linux-64.lock

# AUTO GENERATED FROM environment.py-3.9.yml, DO NOT MANUALLY MODIFY
# Frozen on 2025-10-16 07:16:41 UTC
# Generated by conda-lock.
# platform: linux-64
# input_hash: bd4d374cae58bd84b0ba870367f38a90b671ab1c952a6cf4a62296b73b6accc9
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https://conda.anaconda.org/conda-forge/noarch/rfc3339-validator-0.1.4-pyhd8ed1ab_1.conda#36de09a8d3e5d5e6f4ee63af49e59706
https://conda.anaconda.org/conda-forge/noarch/rfc3987-syntax-1.1.0-pyhe01879c_1.conda#7234f99325263a5af6d4cd195035e8f2
https://conda.anaconda.org/conda-forge/noarch/stack_data-0.6.3-pyhd8ed1ab_1.conda#b1b505328da7a6b246787df4b5a49fbc
https://conda.anaconda.org/conda-forge/noarch/terminado-0.18.1-pyh0d859eb_0.conda#efba281bbdae5f6b0a1d53c6d4a97c93
https://conda.anaconda.org/conda-forge/noarch/tinycss2-1.4.0-pyhd8ed1ab_0.conda#f1acf5fdefa8300de697982bcb1761c9
https://conda.anaconda.org/conda-forge/noarch/typing-extensions-4.14.1-h4440ef1_0.conda#75be1a943e0a7f99fcf118309092c635
https://conda.anaconda.org/conda-forge/noarch/typing-inspection-0.4.1-pyhd8ed1ab_0.conda#e0c3cd765dc15751ee2f0b03cd015712
https://conda.anaconda.org/conda-forge/noarch/annotated-types-0.7.0-pyhd8ed1ab_1.conda#2934f256a8acfe48f6ebb4fce6cde29c
https://conda.anaconda.org/conda-forge/noarch/anyio-4.10.0-pyhe01879c_0.conda#cc2613bfa71dec0eb2113ee21ac9ccbf
https://conda.anaconda.org/conda-forge/linux-64/argon2-cffi-bindings-25.1.0-py39hd399759_0.conda#dfa88a4227076fa51b9a8afd0ed06cee
https://conda.anaconda.org/conda-forge/noarch/arrow-1.3.0-pyhd8ed1ab_1.conda#46b53236fdd990271b03c3978d4218a9
https://conda.anaconda.org/conda-forge/noarch/beautifulsoup4-4.13.4-pyha770c72_0.conda#9f07c4fc992adb2d6c30da7fab3959a7
https://conda.anaconda.org/conda-forge/noarch/bleach-with-css-6.2.0-h82add2a_4.conda#a30e9406c873940383555af4c873220d
https://conda.anaconda.org/conda-forge/linux-64/cryptography-45.0.6-py39hb2f7f84_0.conda#09c640d5a5798c2f520baf821a0fc0fa
https://conda.anaconda.org/conda-forge/noarch/fqdn-1.5.1-pyhd8ed1ab_1.conda#d3549fd50d450b6d9e7dddff25dd2110
https://conda.anaconda.org/conda-forge/noarch/ipython-8.18.1-pyh707e725_3.conda#15c6f45a45f7ac27f6d60b0b084f6761
https://conda.anaconda.org/conda-forge/noarch/jsonschema-specifications-2025.4.1-pyh29332c3_0.conda#41ff526b1083fde51fbdc93f29282e0e
https://conda.anaconda.org/conda-forge/noarch/jupyter_client-8.6.3-pyhd8ed1ab_1.conda#4ebae00eae9705b0c3d6d1018a81d047
https://conda.anaconda.org/conda-forge/noarch/jupyter_server_terminals-0.5.3-pyhd8ed1ab_1.conda#2d983ff1b82a1ccb6f2e9d8784bdd6bd
https://conda.anaconda.org/conda-forge/noarch/mako-1.3.10-pyhd8ed1ab_0.conda#c5bb3eea5f1a00fcf3d7ea186209ce33
https://conda.anaconda.org/conda-forge/linux-64/pydantic-core-2.33.2-py39h20260ba_0.conda#38b79310c98c3a2270e1d19589205a6a
https://conda.anaconda.org/conda-forge/linux-64/sqlalchemy-2.0.43-py39hd399759_0.conda#227867c51ee09b270f31ca28221e57d1
https://conda.anaconda.org/conda-forge/linux-64/zstandard-0.23.0-py39hd399759_3.conda#2f6845f6cdf545845a60c4dcbd017c78
https://conda.anaconda.org/conda-forge/noarch/alembic-1.16.4-pyhd8ed1ab_0.conda#b17cf31f353008d23a6fd8bd90efcfc2
https://conda.anaconda.org/conda-forge/noarch/argon2-cffi-25.1.0-pyhd8ed1ab_0.conda#8ac12aff0860280ee0cff7fa2cf63f3b
https://conda.anaconda.org/conda-forge/noarch/certipy-0.2.2-pyhd8ed1ab_0.conda#7bacdbd6bb3b4fe905a3235d2799ca78
https://conda.anaconda.org/conda-forge/noarch/httpcore-1.0.9-pyh29332c3_0.conda#4f14640d58e2cc0aa0819d9d8ba125bb
https://conda.anaconda.org/conda-forge/noarch/ipykernel-6.30.1-pyh82676e8_0.conda#b0cc25825ce9212b8bee37829abad4d6
https://conda.anaconda.org/conda-forge/noarch/ipywidgets-8.1.7-pyhd8ed1ab_0.conda#7c9449eac5975ef2d7753da262a72707
https://conda.anaconda.org/conda-forge/noarch/isoduration-20.11.0-pyhd8ed1ab_1.conda#0b0154421989637d424ccf0f104be51a
https://conda.anaconda.org/conda-forge/noarch/jsonschema-4.25.1-pyhe01879c_0.conda#341fd940c242cf33e832c0402face56f
https://conda.anaconda.org/conda-forge/noarch/oauthlib-3.3.1-pyhd8ed1ab_0.conda#d4f3f31ee39db3efecb96c0728d4bdbf
https://conda.anaconda.org/conda-forge/noarch/pydantic-2.11.7-pyh3cfb1c2_0.conda#1b337e3d378cde62889bb735c024b7a2
https://conda.anaconda.org/conda-forge/noarch/urllib3-2.5.0-pyhd8ed1ab_0.conda#436c165519e140cb08d246a4472a9d6a
https://conda.anaconda.org/conda-forge/noarch/httpx-0.28.1-pyhd8ed1ab_0.conda#d6989ead454181f4f9bc987d3dc4e285
https://conda.anaconda.org/conda-forge/noarch/jsonschema-with-format-nongpl-4.25.1-he01879c_0.conda#13e31c573c884962318a738405ca3487
https://conda.anaconda.org/conda-forge/noarch/nbformat-5.10.4-pyhd8ed1ab_1.conda#bbe1963f1e47f594070ffe87cdf612ea
https://conda.anaconda.org/conda-forge/noarch/requests-2.32.5-pyhd8ed1ab_0.conda#db0c6b99149880c8ba515cf4abe93ee4
https://conda.anaconda.org/conda-forge/noarch/jupyter_events-0.12.0-pyh29332c3_0.conda#f56000b36f09ab7533877e695e4e8cb0
https://conda.anaconda.org/conda-forge/noarch/nbclient-0.10.2-pyhd8ed1ab_0.conda#6bb0d77277061742744176ab555b723c
https://conda.anaconda.org/conda-forge/noarch/jupyterhub-base-5.3.0-pyhda7c55b_0.conda#2a47623cd374e67413707b9925908313
https://conda.anaconda.org/conda-forge/noarch/nbconvert-core-7.16.6-pyh29332c3_0.conda#d24beda1d30748afcc87c429454ece1b
https://conda.anaconda.org/conda-forge/noarch/jupyter_server-2.16.0-pyhe01879c_0.conda#f062e04d7cd585c937acbf194dceec36
https://conda.anaconda.org/conda-forge/noarch/jupyter-lsp-2.2.6-pyhe01879c_0.conda#7129ed52335cc7164baf4d6508a3f233
https://conda.anaconda.org/conda-forge/noarch/jupyter-offlinenotebook-0.3.1-pyh885dcc9_1.conda#aff9028145d26b0987d0959a989e40cf
https://conda.anaconda.org/conda-forge/noarch/jupyter-resource-usage-1.2.0-pyhd8ed1ab_0.conda#9ef4adccd3a32f3f01fc998f2ad4bdf5
https://conda.anaconda.org/conda-forge/noarch/jupyterlab_server-2.27.3-pyhd8ed1ab_1.conda#9dc4b2b0f41f0de41d27f3293e319357
https://conda.anaconda.org/conda-forge/noarch/notebook-shim-0.2.4-pyhd8ed1ab_1.conda#e7f89ea5f7ea9401642758ff50a2d9c1
https://conda.anaconda.org/conda-forge/noarch/jupyterlab-4.4.6-pyhd8ed1ab_0.conda#70cb2903114eafc6ed5d70ca91ba6545
https://conda.anaconda.org/conda-forge/noarch/jupyterhub-singleuser-5.3.0-h4422900_0.conda#c4e0da69399fb5bd8e314ec2da0f0119
https://conda.anaconda.org/conda-forge/noarch/notebook-7.4.5-pyhd8ed1ab_0.conda#28062c17cdb444388c00903eaec1ba0e

With 2.6.2:

MAMBA_USE_SHARDED_REPOPATA=0 micromamba env update -p /tmp/env -f /tmp/downgrade.yml                                                 

Using Flat Repodata for conda-forge/linux-64                                              ✔ Done (4.6 sec) 
Using Flat Repodata for conda-forge/noarch                                                ✔ Done (1.9 sec) 
Parsing Packages' Records                                                                 ✔ Done (6.5 sec) 
                                                                                                           
Resolving Environment                                                                    ✔ Done (27.9 sec)