This patch series contains the following changes:
- Incorporation of `crypt_sha512.c` from musl to out codebase
- Conversion of `crypt_sha512.c` to C++ and coroutinization
- Coroutinization of `auth::passwords::check`
- Enabling use of `__crypt_sha512` orignated from `crypt_sha512.c` for
computing SHA 512 passwords of length <=255
- Addition of yielding in the aforementioned hashing implementation.
The alien thread was a solution for reactor stalls caused by indivisible
password‑hashing tasks (https://github.com/scylladb/scylladb/issues/24524).
However, because there is only one alien thread, overall hashing throughput was reduced
(see, e.g., https://github.com/scylladb/scylla-enterprise/issues/5711). To address this,
the alien‑thread solution is reverted, and a hashing implementation
with yielding is introduced in this patch series.
Before this patch series, ScyllaDB used SHA-512 hashing provided
by the `crypt_r` function, which in our case meant using the implementation
from the `libxcrypt` library. Adding yielding to this `libxcrypt`
implementation is problematic, both due to licensing (LGPL) and because the
implementation is split into many functions across multiple files. In
contrast, the SHA-512 implementation from `musl libc` has a more
permissive license and is concise, which makes it easier to incorporate
into the ScyllaDB codebase.
The performance of this solution was compared with the previous
implementation that used one alien thread and the implementation
after the alien thread was reverted. The results (median) of
`perf-cql-raw` with `--connection-per-request 1 --smp 10` parameters
are as follows:
- Alien thread: 41.5 new connections/s per shard
- Reverted alien thread: 244.1 new connections/s per shard
- This commit (yielding in hashing): 198.4 new connections/s per shard
The roughly 20% performance deterioration compared to
the old implementation without the alien thread comes from the fact
that the new hashing algorithm implemented in `utils/crypt_sha512.cc`
performs an expensive self-verification and stack cleanup.
On the other hand, with smp=10 the current implementation achieves
roughly 5x higher throughput than the alien thread. In addition,
due to yielding added in this commit, the algorithm is expected
to provide similar protection from stalls as the alien thread did.
In a test that in parallel started a cassandra-stress workload and
created thousands of new connections using python-driver, the values of
`scylla_reactor_stalls_count` metric were as follows:
- Alien thread: 109 stalls/shard total
- Reverted alien thread: 13186 stalls/shard total
- This commit (yielding in hashing): 149 stalls/shard total
Similarly, the `scylla_scheduler_time_spent_on_task_quota_violations_ms`
values were:
- Alien thread: 1087 ms/shard total
- Reverted alien thread: 72839 ms/shard total
- This commit (yielding in hashing): 1623 ms/shard total
To summarize, yielding during hashing computations achieves similar
throughput to the old solution without the alien thread but also
prevents stalls similarly to the alien thread.
Fixes: scylladb/scylladb#26859
Refs: scylladb/scylla-enterprise#5711
No automatic backport. After this PR is completed, the alien thread should be rather reverted from older branches (2025.2-2025.4 because on 2025.1 it's already removed). Backporting of the other commits needs further discussion.
Closesscylladb/scylladb#26860
* github.com:scylladb/scylladb:
test/boost: add too_long_password to auth_passwords_test
test/boost: add same_hashes_as_crypt_r to auth_passwords_test
auth: utils: add yielding to crypt_sha512
auth: change return type of passwords::check to future
auth: remove code duplication in verify_scheme
test/boost: coroutinize auth_passwords_test
utils: coroutinize crypt_sha512
utils: make crypt_sha512.cc to compile
utils: license: import crypt_sha512.c from musl to the project
Revert "auth: move passwords::check call to alien thread"
c06e63daed