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Mongodb Avx Qemu

docs/Databases/mongodb-avx-qemu.md

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Built-in: WeKan cpu-exec runs binaries with qemu-user automatically

Since WeKan 9.96 (issue #6458), WeKan ships a general cpu-exec helper on every Linux platform — in the Snap ($SNAP/bin/cpu-exec), in every wekan-<version>-<arch>.zip bundle (bundle/cpu-exec, next to a same-arch qemu-<arch> static binary), in the Docker image (/build/cpu-exec) and in the Sandstorm .spk. It checks /proc/cpuinfo for the CPU features a binary needs and, when one is missing, transparently re-runs the binary through qemu-user (which implements the full modern instruction set):

cpu-exec --features x86_64=avx,aarch64=atomics mongod --dbpath ...
  • With no --features (or no entry for the current architecture) it is a plain exec — zero overhead, safe for every binary.
  • WEKAN_REQUIRED_CPU_FEATURES (same syntax) overrides --features, so any script or user can declare requirements without editing commands.
  • qemu-user lookup order: $WEKAN_QEMU_USER, qemu-<arch> next to cpu-exec (the bundle), $SNAP/qemu-<arch>, the Snap's migratemongo/avx/qemu-x86_64, then qemu-<arch>/ qemu-<arch>-static on $PATH (install with sudo apt install qemu-user-static).
  • aarch64=atomics (LSE, ARMv8.1) is the practical /proc/cpuinfo proxy for MongoDB's ARMv8.2-A requirement: Raspberry Pi 3/4 (Cortex-A53/A72) lack it, ARMv8.2-A cores have it.

The Snap's mongodb-control and migration-control run every mongod 7 invocation through cpu-exec, so WeKan's MongoDB works (slower) on CPUs without AVX — including hypervisors/sandboxes that mask AVX — and the MongoDB → FerretDB migration can read modern MongoDB data there too. FerretDB (pure Go + SQLite) needs no special CPU features and is the native-speed alternative: snap run wekan.migrate.

Meteor podcast about using MongoDB at unsupported CPUs

MongoDB Operating System Support precompiled binaries

  • arm64: Only Ubuntu. No Raspberry Pi OS, Alpine Linux.
    • But installing .deb packages to Raspberry Pi 5 running Raspberry OS 64bit can have hardware running cooler, than on Ubuntu.
  • For anything else, see MongoDB download page.

MongoDB CPU support

New MongoDB supports newer CPUs only, like:

  • x86_64 that have AVX instructions, from MongoDB 5 and later
  • ARMv8.2-A microarchitecture, from MongoDB 4.4.19, 5.0, 6.0 and later, like:
    • Raspberry Pi 5
    • OrangePi 5
    • Apple Silicon arm64

Old MongoDB 4.4.18 supports old CPUs, like:

Info about requiring newer arm64:

Detecting does x86_64 CPU support AVX:

Error running MongoDB 8 at RasPi4, when not using Qemu:

December 06 11:48:49 rpi4b systemd[1]: Started mongod.service - MongoDB Database Server.
December 06 11:48:53 rpi4b mongod[3749]: /usr/bin/mongod: line 4:  3750 Illegal instruction     (core dumped) /usr/bin/mongodreal --co>
December 06 11:48:53 rpi4b systemd[1]: mongod.service: Main process exited, code=exited, status=132/n/a
December 06 11:48:53 rpi4b systemd[1]: mongod.service: Failed with result 'exit-code'.

a) Prebuilt binary

MongoDB 7.3.4 for RasPi4 and older:

b) Compile MongoDB, takes a lot of time

CrossCompiling MongoDB from x86_64 to ARMv8.0 Cortex A53/A55/A72 like RasPi4 and older:

Compiling MongoDB from x86_64 to x86_64 CPUs that does not have AVX instructions:

c) Run MongoDB with Qemu, that supports newest CPU features

qemu-user can run single Linux executeable for many architectures. It does not emulate full OS like qemu-system.

Running MongoDB with Qemu on x86_64 CPU that does not support AVX, like Intel Core 2 Duo:

Running MongoDB with Qemu on older arm64, like RasPi4 and older RasPi: