160 lines
5.6 KiB
Markdown
160 lines
5.6 KiB
Markdown
Turbo NSS
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---------
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Turbonss is a plugin for GNU Name Service Switch ([NSS][nsswitch])
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functionality of GNU C Library (glibc). Turbonss implements lookup for `user`
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and `passwd` database entries (i.e. system users, groups, and group
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memberships). It's main goal is to run [`id(1)`][id] as fast as possible.
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Turbonss is optimized for reading. If the data changes in any way, the whole
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file will need to be regenerated. Therefore, it was created, and best suited,
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for environments that have a central user & group database which then needs to
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be distributed to many servers/services, and the data does not change very
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often (e.g. hourly).
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This is the fastest known NSS passwd/group implementation for *reads*. On a
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corpus with 10k users, 10k groups and 500 average members per group, `id` takes
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17 seconds with the glibc default implementation, 10-17 milliseconds with a
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pre-cached `nscd`, ~8 milliseconds with `turbonss`.
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Project status
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--------------
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The project is finished and is not recommended for production; just use nscd.
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Turbonss duly implements the full user/group API in `src/libnss.zig`: feel free
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to copy that. turbonss is only 2-5 times faster than nscd, which usually does
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not matter (including for my original use case).
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Yours truly (the author) worked on this for about 7 months. And when this was
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finished it turned out that just slapping nscd on top of the existing NSS
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implementation is fast enough.
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Dependencies
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------------
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1. zig v0.10. turbonss uses stage1 (the C++ version) and is not compatible with
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stage2.
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2. [cmph][cmph]: bundled with this repository.
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Trying it out
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-------------
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Clone, compile and test first:
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$ git clone --recursive https://git.sr.ht/~motiejus/turbonss
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$ zig build test
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$ zig build -Dtarget=x86_64-linux-gnu.2.31 -Dcpu=x86_64_v3 -Drelease-safe=true
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One may choose different options, depending on requirements. Here are some
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hints:
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1. `-Dcpu=<...>` for the CPU
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[microarchitecture](https://en.wikipedia.org/wiki/X86-64#Microarchitecture_levels).
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2. `-Drelease-fast=true` for max speed
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3. `-Drelease-small=true` for smallest binary sizes.
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4. `-Dstrip=true` to strip debug symbols.
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Test it on a real system
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------------------------
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`db.turbo` is the TurboNSS database file. To create one from `/etc/group` and
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`/etc/passwd`, use `turbonss-unix2db`:
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$ zig-out/bin/turbonss-unix2db --passwd /etc/passwd --group /etc/group
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$ zig-out/bin/turbonss-analyze db.turbo
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File: /etc/turbonss/db.turbo
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Size: 2,624 bytes
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Version: 0
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Endian: little
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Pointer size: 8 bytes
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getgr buffer size: 17
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getpw buffer size: 74
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Users: 19
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Groups: 39
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Shells: 1
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Most memberships: _apt (1)
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Sections:
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Name Begin End Size bytes
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header 00000000 00000080 128
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bdz_gid 00000080 000000c0 64
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bdz_groupname 000000c0 00000100 64
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bdz_uid 00000100 00000140 64
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bdz_username 00000140 00000180 64
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idx_gid2group 00000180 00000240 192
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idx_groupname2group 00000240 00000300 192
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idx_uid2user 00000300 00000380 128
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idx_name2user 00000380 00000400 128
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shell_index 00000400 00000440 64
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shell_blob 00000440 00000480 64
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groups 00000480 00000700 640
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users 00000700 000009c0 704
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groupmembers 000009c0 00000a00 64
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additional_gids 00000a00 00000a40 64
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Run and configure a test container that uses `turbonss` instead of the default
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`files`:
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$ docker run -ti --rm -v `pwd`:/etc/turbonss -w /etc/turbonss debian:bullseye
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# cp zig-out/lib/libnss_turbo.so.2 /lib/x86_64-linux-gnu/
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# sed -i '/passwd\|group/ s/files/turbo/' /etc/nsswitch.conf
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And run the commands:
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$ getent passwd
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$ getent group
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$ id root
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More users and groups
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---------------------
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`turbonss-makecorpus` can synthesize more `users` and `groups`:
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# ./zig-out/bin/turbonss-makecorpus
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wrote users=10000 groups=10000 avg-members=1000 to .
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# cat group >> /etc/group
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# cat passwd >> /etc/passwd
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# time id u_1000000
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<...>
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real 0m17.380s
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user 0m13.117s
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sys 0m4.263s
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17 seconds for an `id` command! Well, there are indeed many users and groups.
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Let's see how turbonss fares with it:
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# zig-out/bin/turbonss-unix2db --group /etc/group --passwd /etc/passwd
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total 10968512 bytes. groups=10019 users=10039
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# ls -hs /etc/group /etc/passwd db.turbo
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48M /etc/group 668K /etc/passwd 11M db.turbo
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# sed -i '/passwd\|group/ s/files/turbo/' /etc/nsswitch.conf
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# time id u_1000000
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real 0m0.008s
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user 0m0.000s
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sys 0m0.008s
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That's ~1500x improvement for the `id` command (and notice about 4X compression
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ratio compared to plain files). If the number of users and groups is increased
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by 10x (to 100k each), the difference becomes even crazier:
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# time id u_1000000
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<...>
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real 3m42.281s
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user 2m30.482s
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sys 0m55.840s
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# sed -i '/passwd\|group/ s/files/turbo/' /etc/nsswitch.conf
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# time id u_1000000
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<...>
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real 0m0.008s
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user 0m0.000s
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sys 0m0.008s
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Documentation
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-------------
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Architecture is detailed in `docs/architecture.md`
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Development notes are in `docs/development.md`
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[nsswitch]: https://linux.die.net/man/5/nsswitch.conf
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[id]: https://linux.die.net/man/1/id
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[cmph]: http://cmph.sourceforge.net/
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