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perf(l1): an encrypted L1 hit walks its decrypted plaintext once (LAB-12915) - #228
An encrypted L1 hit decrypted its ciphertext and then ran cachekit-core's msgpack_document_len bounds walk on the plaintext on every hit, although the walk's verdict on that plaintext cannot change while L1 holds the same ciphertext. This PR walks it once. The first L1 hit whose decrypted plaintext passes the walk marks the L1 entry, and later hits on that ciphertext decrypt and then decode without the walk. An encrypted 20-field struct hit at 40 B goes from 15,170 to 12,733 Ir/op (−16.1%).
How
One mark per kind of decode.Payload's walked flag becomes Walked { No, Bytes, Plaintext }. Payload::deserializer, the path of a client without encryption, honours only Bytes. The new Decrypted::deserializer honours only Plaintext. A mark one kind of decode earned is never trusted by the other. Ciphertext whose first byte is below 0x80 can itself pass the walk, so a single bool would be safe only for as long as every read path routes an encrypting client through SecureCache.
Only a passing walk mints the mark.Payload::decrypt keeps the plaintext together with the ciphertext it came from, as Decrypted. Decrypted::deserializer records that its own walk passed. Decrypted::marked is the only way to build a Plaintext-marked payload, and it returns one only after that walk passed. Payload's fields stay private to the serializer module, so no other code can pair a mark with other bytes.
The mark lands only on the entry the hit read.L1Cache::adopt swaps the marked payload in under the shard's write lock (quick_cacheentry), and only if the entry still holds the same Bytes buffer (pointer and length). A write, delete or eviction during the hit leaves L1 as it left it, and an absent key gains no entry. The read still holds a reference to the buffer, so its address cannot be reused while the two are compared. TTL and freshness are unchanged.
Marked on L1 hits only. An L2 hit decodes with the walk and marks nothing, so a key read once costs no extra L1 write. Marking the backfilled entry on L2 hits measured +6% on l2_hit/enc.
Own writes are walked too. A write is admitted unwalked, and its first L1 hit walks it. rmp-serde 1.3.1 does not count enum nesting against its depth limit, so "this process wrote it" is no reason to trust bytes (as in #214).
The mark records the walk, not the decode. A plaintext that passes the walk but does not decode as the requested type is still marked, and the type error is still returned, with the decoder's message redacted as before.
Why the same ciphertext always yields the same verdict
Every read still decrypts and authenticates. A client's keyring is fixed when it is built: the current key is tried first, then each previous key in a fixed order. The AAD binds the storage key the entry was read under, so the same ciphertext read for the same key either fails authentication or decrypts to the same plaintext. L1 is private to one client, and Bytes cannot be modified in place while L1 holds a reference to it. No backend can rewrite a marked buffer: every backend read returns a fresh Vec<u8>, and the copy a write hands the backend is an immutable Bytes.
How this differs from the bit cachekit-io/cachekit-py#671 declined. The mark is never stored, sent or read from any backend: it lives in this process's L1 entry and nowhere else. This process sets it only after its own decrypt and its own walk of the same immutable ciphertext pass. It records only that the plaintext parses within the decode bounds, which every successful read already shows. No AAD, key, nonce or wire byte changes.
Read paths
Path
Covered
SecureCache::get (and CacheKit::get on an encrypting client)
yes
SecureCache::interop_get
yes
SecureCache::interop_get_swr, Fresh and Stale
yes
#[cachekit(secure)] reads (__interop_read, __interop_read_swr, Fresh and Stale)
yes
Previous-key reads (prev)
yes: the same paths, with a decrypt that tries each previous key in a fixed order
Namespaced encrypting client (nsenc)
yes: the same paths; the AAD binds the prefixed key
wasm32
not applicable: no L1
Public L1Cache::set
stays unwalked under both marks
Instruction counts
From make bench-instr BASE=<base>: callgrind, median of 5 ABBA runs, release build with --features macros. The base is main plus this PR's first commit, which only adds the l1_hit_row/enc case, so both builds run the same workload. The two binaries sat at paths of equal length. Cells inside the gate's noise floor say "noise".
Case
40 B
64 B
1 KiB
64 KiB
l1_hit_row/enc (new: a 20-field struct)
15,170 → 12,733 (−16.1%)
15,078 → 12,641 (−16.2%)
18,263 → 15,824 (−13.4%)
342,390 → 339,952 (−0.7%)
l1_hit/enc (String)
4,954 → 4,920 (−0.7%)
5,062 → 5,028 (−0.7%)
noise (−0.4%)
noise
l1_hit/nsenc
5,214 → 5,183 (−0.6%)
5,328 → 5,297 (−0.6%)
noise (−0.4%)
noise
macro_hit/enc¹
9,738 → 9,633 (−1.1%)
9,852 → 9,747 (−1.1%)
13,212 → 13,103 (−0.8%)
noise
macro_hit/plain, macro_hit/rel¹
5,508 → 5,471 (−0.7%)
5,555 → 5,518 (−0.7%)
6,084 → 6,047 (−0.6%)
noise
¹ Measured at the head against main with bench_hot_path instr --base, from another build of both binaries than the rows above, so their absolute counts differ. That run passes all 122 cases.
l1_hit/plain, l1_hit_row/plain, l1_hit/prev, l2_hit/* and oneshot/* are inside their floors. set/* (−0.6% to −1.1%) and exists/* (−6.7%) read faster although this PR does not touch either path.
A/A. A second build of the base source, from a different checkout of equal path length, measured against the base binary: all 120 gated cases are inside their floors. Only the ungated delete cases flag, at a 7% run-to-run spread.
macro_hit. The plain and secure #[cachekit] reads share one poll function, which is generic and so instantiated in the calling crate. An encrypting client's read used to await a secure read future stored inside the plain read's future, so the mark's change to the secure read added 34 Ir/op to macro_hit/plain and macro_hit/rel: moves of the resolved key, with no new code run. The read now awaits read_bytes_swr once and branches afterwards to SecureCache::open_swr, a synchronous decrypt and decode. The same change on main alone moves macro_hit/plain at 40 B from 5,508 to 5,474, and adding the mark then moves it to 5,471, so the plain read no longer depends on the secure read's code.
The trade: a key read once from L1 pays one quick_cacheentry call on its first hit. Every later hit on it saves the walk, about 2,400 Ir for the 20-field struct and 34 for a 40 B string.
Tests
sealed_hostile_plaintext_fails_from_the_backend_and_every_time_from_l1: every reject vector of the protocol's decode-bounds.json, plus a 60-level recursive enum, is sealed under the client's own key and read by all five secure read paths. Each read is refused from the backend, from L1, and from L1 again. rmp-serde alone decodes the enum, so a wrongly set mark shows up as a successful read.
every_sealed_accept_vector_decodes_from_the_backend_and_from_l1: the backend read, the hit that walks and marks, and the marked hit decode to the same value.
an_own_encrypted_write_of_a_deep_recursive_enum_fails_from_l1_every_time, the encrypting twin of #214's an_own_write_of_a_deep_recursive_enum_fails_from_l1, which still passes.
client::plaintext_mark_tests: an own write is unmarked until its first L1 hit; an L2 hit marks nothing and the next L1 hit marks; a passing walk marks even when the requested type does not fit; a mark never lands on a rewritten or deleted entry, and adds no entry; the public L1Cache::set stays unwalked.
Mutation checks: admitting every ciphertext already marked fails the hostile-plaintext, own-write and mark tests. Swapping in the marked payload without the buffer check fails the rewrite test.
make quick-check passes (690 tests). clippy --lib -D warnings also passes with encryption, l1, l1,encryption,unsync, redis, memcached and cachekitio,encryption alone, and the wasm32 workers,encryption check passes.
Docs
README. The decode-bounds paragraph now says where an encrypting client walks: on decrypted plaintext until an L1 hit's plaintext passes. The bench note now lists l1_hit_row's enc mode.
Rustdoc.MAX_DECODE_DEPTH, bounded_deserializer, Payload, Walked, Decrypted and L1Cache::adopt say where the walk runs, which function mints each mark, and which decode honours it.
No actionable comments were generated in the recent review.
Summary by CodeRabbit
Bug Fixes
Encrypted reads now validate decrypted data on the first eligible L1 hit and reuse successful validation on later hits. Rewrites, deletions and evictions clear the validation mark.
Invalid data remains unmarked, and L2 reads do not receive the L1 validation mark.
Added coverage for invalid and deeply nested data across backend and repeated L1 reads.
Documentation
Clarified when decode validation runs and how successful validation is remembered.
Documented plaintext and encrypted l1_hit_row benchmark modes.
Walkthrough
Encrypted reads validate decrypted plaintext through a shared decode path. After a successful structural walk, an L1 hit can adopt a mark that skips later walks for the same ciphertext. Tests cover repeated reads, decode errors and entry changes.
Changes
Encrypted decode-bound validation
Layer / File(s)
Summary
Track byte and plaintext validation crates/cachekit/src/serializer/mod.rs, crates/cachekit/src/interop.rs
Payloads track whether stored bytes or decrypted plaintext passed the structural walk. The decrypted deserializer checks plaintext unless its ciphertext has a matching mark.
Decode and adopt encrypted L1 payloads crates/cachekit/src/client.rs, crates/cachekit/src/l1/mod.rs
Secure read paths use a shared decode flow. It adopts a marked payload on L1 hits only when the stored entry still has the same buffer. Serialization errors remain redacted to the target type; other errors pass through.
Tests cover accepted and rejected plaintext on backend and repeated L1 reads, including deep values and entry changes. The benchmark and documentation cover encrypted row reads and plaintext validation behaviour.
sequenceDiagram
participant Client
participant Payload
participant Decrypted
participant L1Cache
Client->>Payload: Decrypt ciphertext
Payload-->>Client: Return Decrypted value
Client->>Decrypted: Decode plaintext and check bounds
Decrypted-->>Client: Return decode result and successful-walk mark
Client->>L1Cache: Adopt marked payload on an L1 hit
L1Cache-->>Client: Replace payload only when the buffer matches
No material issue remains identified that would prevent merging after normal checks.
Pre-merge checks: 5
Check name
Status
Explanation
Title check
The title names the main change: an encrypted L1 hit walks its decrypted plaintext once, which is the core of the perf change. The changeset adds the plaintext mark (Walked::Plaintext, Decrypted, L1Ca…
Description check
The description explains the change in detail. It covers why the bounds walk repeats on encrypted L1 hits, how the new Walked state and L1Cache::adopt work, which read paths are covered, and the bench…
Docstring Coverage
Docstring coverage is 86.96% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentati…
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
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Full details: Title check
Explanation
The title names the main change: an encrypted L1 hit walks its decrypted plaintext once, which is the core of the perf change. The changeset adds the plaintext mark (Walked::Plaintext, Decrypted, L1Cache::adopt) so later hits skip the bounds walk. The title uses the conventional perf(l1) prefix and the Jira reference, and is specific enough for a teammate scanning history.
Full details: Description check
Explanation
The description explains the change in detail. It covers why the bounds walk repeats on encrypted L1 hits, how the new Walked state and L1Cache::adopt work, which read paths are covered, and the benchmark and test results. It matches the changeset closely.
Full details: Docstring Coverage
Explanation
Docstring coverage is 86.96% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 23 functions across 7 files.
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crates/cachekit/src/client.rs
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Actionable comments posted: 3
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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Inline comments:
Review comments at @crates/cachekit/src/client.rs:
- Around line 2695-2700: Update the loop around client.get and is_marked to
assert the walk count after each hit: the first encrypted L1 hit must walk once,
and the second must not increase the count. Use the test’s existing walk-count
instrumentation and preserve the value and mark assertions.
Review comments at @crates/cachekit/tests/common/mod.rs:
- Around line 250-255: Add a test near the repeated-read tests using an unmarked
stale encrypted entry. Assert that the first stale read adopts the stale mark
and that a subsequent stale read skips the walk; do not rely only on
decoded-value comparisons.
Review comments at @crates/cachekit/tests/decode_bounds_tests.rs:
- Around line 255-260: Add a sealed backend-and-L1 regression test alongside the
`read_every_path_sealed_through_l1` coverage, using a tag-only ext target type
that accepts the vector without reading its missing body. Assert that the
overclaimed ext vector still returns `CachekitError::Serialization` on the
backend, L1, and repeated L1 reads, rather than relying on `Node`, which may
fail due to a type mismatch.
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README.md
crates/cachekit/examples/bench_hot_path.rs
crates/cachekit/src/client.rs
crates/cachekit/src/interop.rs
crates/cachekit/src/l1/mod.rs
crates/cachekit/src/serializer/mod.rs
crates/cachekit/tests/common/mod.rs
crates/cachekit/tests/decode_bounds_tests.rs
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122 of 122 cases measured. A case fails when its median is slower than the base by its floor or more (SLOWER). The floor is 0.5%, and such a case also fails when the head's runs spread by more than that (NOISIER), except l2_hit, whose floor is 2% because its count varies between runs. delete cases are reported, never failed. Method: README, Measuring performance.
Verdict
Case
Base Ir/op
Head Ir/op
Delta
Floor
Head spread
faster
l1_hit/plain/40
1304
1284
-1.53%
0.50%
0.00%
faster
l1_hit/plain/64
1351
1331
-1.48%
0.50%
0.00%
faster
l1_hit/plain/1024
1880
1860
-1.06%
0.50%
0.00%
faster
l1_hit/rel/40
1304
1284
-1.53%
0.50%
0.00%
faster
l1_hit/rel/64
1351
1331
-1.48%
0.50%
0.00%
faster
l1_hit/rel/1024
1880
1860
-1.06%
0.50%
0.00%
faster
l1_hit/enc/40
4726
4689
-0.78%
0.50%
0.00%
faster
l1_hit/enc/64
4840
4803
-0.76%
0.50%
0.00%
faster
l1_hit/ns/40
1503
1485
-1.20%
0.50%
0.00%
faster
l1_hit/ns/64
1547
1529
-1.16%
0.50%
0.00%
faster
l1_hit/ns/1024
2082
2064
-0.86%
0.50%
0.00%
faster
l1_hit/nsenc/40
4925
4891
-0.69%
0.50%
0.00%
faster
l1_hit/nsenc/64
5039
5005
-0.67%
0.50%
0.00%
faster
l1_hit_row/enc/40
14288
11921
-16.57%
0.50%
0.00%
faster
l1_hit_row/enc/64
14197
11830
-16.67%
0.50%
0.00%
faster
l1_hit_row/enc/1024
17393
15024
-13.62%
0.50%
0.00%
faster
l1_hit_row/enc/65536
341485
339117
-0.69%
0.50%
0.00%
faster
set/plain/40
4553
4507
-1.01%
0.50%
0.00%
faster
set/plain/64
4560
4514
-1.01%
0.50%
0.00%
faster
set/plain/1024
4704
4658
-0.98%
0.50%
0.00%
faster
set/rel/40
5339
5293
-0.86%
0.50%
0.00%
faster
set/rel/64
5373
5327
-0.86%
0.50%
0.00%
faster
set/rel/1024
5493
5447
-0.84%
0.50%
0.00%
faster
set/enc/40
7701
7655
-0.60%
0.50%
0.00%
faster
set/enc/64
7766
7720
-0.59%
0.50%
0.00%
faster
set/ns/40
4765
4719
-0.97%
0.50%
0.00%
faster
set/ns/64
4782
4736
-0.96%
0.50%
0.00%
faster
set/ns/1024
4924
4878
-0.93%
0.50%
0.00%
faster
set/nsenc/40
7891
7845
-0.58%
0.50%
0.00%
faster
set/nsenc/64
7993
7947
-0.58%
0.50%
0.00%
faster
exists/plain/40
779
722
-7.32%
0.50%
0.00%
faster
exists/plain/64
779
722
-7.32%
0.50%
0.00%
faster
exists/plain/1024
779
722
-7.32%
0.50%
0.00%
faster
exists/plain/65536
785
728
-7.26%
0.50%
0.00%
faster
exists/rel/40
779
722
-7.32%
0.50%
0.00%
faster
exists/rel/64
779
722
-7.32%
0.50%
0.00%
faster
exists/rel/1024
779
722
-7.32%
0.50%
0.00%
faster
exists/rel/65536
785
728
-7.26%
0.50%
0.00%
faster
exists/enc/40
797
740
-7.15%
0.50%
0.00%
faster
exists/enc/64
797
740
-7.15%
0.50%
0.00%
faster
exists/enc/1024
797
740
-7.15%
0.50%
0.00%
faster
exists/enc/65536
803
746
-7.10%
0.50%
0.00%
faster
macro_hit/plain/40
5240
5203
-0.71%
0.50%
0.00%
faster
macro_hit/plain/64
5287
5250
-0.70%
0.50%
0.00%
faster
macro_hit/plain/1024
5816
5779
-0.64%
0.50%
0.00%
faster
macro_hit/rel/40
5240
5203
-0.71%
0.50%
0.00%
faster
macro_hit/rel/64
5287
5250
-0.70%
0.50%
0.00%
faster
macro_hit/rel/1024
5816
5779
-0.64%
0.50%
0.00%
faster
macro_hit/enc/40
9329
9224
-1.13%
0.50%
0.00%
faster
macro_hit/enc/64
9443
9338
-1.11%
0.50%
0.00%
faster
macro_hit/enc/1024
12797
12690
-0.84%
0.50%
0.00%
71 cases within noise
Verdict
Case
Base Ir/op
Head Ir/op
Delta
Floor
Head spread
within noise
l1_hit/plain/65536
95711
95691
-0.02%
0.50%
0.00%
within noise
l1_hit/rel/65536
95727
95707
-0.02%
0.50%
0.00%
within noise
l1_hit/enc/1024
8184
8145
-0.48%
0.50%
0.00%
within noise
l1_hit/enc/65536
331697
331659
-0.01%
0.50%
0.00%
within noise
l1_hit/prev/40
7618
7587
-0.41%
0.50%
0.00%
within noise
l1_hit/prev/64
7806
7775
-0.40%
0.50%
0.00%
within noise
l1_hit/prev/1024
14046
14013
-0.23%
0.50%
0.00%
within noise
l1_hit/prev/65536
632714
632682
-0.01%
0.50%
0.00%
within noise
l1_hit/ns/65536
95907
95889
-0.02%
0.50%
0.00%
within noise
l1_hit/nsenc/1024
8395
8359
-0.43%
0.50%
0.00%
within noise
l1_hit/nsenc/65536
331928
331893
-0.01%
0.50%
0.00%
within noise
l1_hit_row/plain/40
7773
7777
+0.05%
0.50%
0.00%
within noise
l1_hit_row/plain/64
7820
7824
+0.05%
0.50%
0.00%
within noise
l1_hit_row/plain/1024
8335
8339
+0.05%
0.50%
0.00%
within noise
l1_hit_row/plain/65536
102320
102324
+0.00%
0.50%
0.00%
within noise
l2_hit/plain/40
6394
6359
-0.55%
2.00%
1.50%
within noise
l2_hit/plain/64
6434
6386
-0.75%
2.00%
0.92%
within noise
l2_hit/plain/1024
7224
7183
-0.57%
2.00%
0.37%
within noise
l2_hit/plain/65536
166736
166535
-0.12%
2.00%
0.13%
within noise
l2_hit/rel/40
7051
7011
-0.57%
2.00%
1.23%
within noise
l2_hit/rel/64
7050
6994
-0.80%
2.00%
1.03%
within noise
l2_hit/rel/1024
7858
7821
-0.47%
2.00%
0.45%
within noise
l2_hit/rel/65536
167384
167209
-0.10%
2.00%
0.12%
within noise
l2_hit/enc/40
9723
9741
+0.18%
2.00%
0.54%
within noise
l2_hit/enc/64
9836
9875
+0.41%
2.00%
0.38%
within noise
l2_hit/enc/1024
13477
13479
+0.02%
2.00%
0.26%
within noise
l2_hit/enc/65536
402744
402770
+0.01%
2.00%
0.04%
within noise
l2_hit/prev/40
12633
12664
+0.25%
2.00%
0.93%
within noise
l2_hit/prev/64
12816
12838
+0.17%
2.00%
0.37%
within noise
l2_hit/prev/1024
19339
19377
+0.20%
2.00%
0.14%
within noise
l2_hit/prev/65536
703794
703720
-0.01%
2.00%
0.03%
within noise
l2_hit/ns/40
6844
6801
-0.63%
2.00%
0.21%
within noise
l2_hit/ns/64
7023
6969
-0.76%
2.00%
0.51%
within noise
l2_hit/ns/1024
7644
7576
-0.89%
2.00%
0.69%
within noise
l2_hit/ns/65536
167148
167138
-0.01%
2.00%
0.14%
within noise
l2_hit/nsenc/40
10402
10434
+0.31%
2.00%
0.49%
within noise
l2_hit/nsenc/64
10342
10371
+0.28%
2.00%
0.59%
within noise
l2_hit/nsenc/1024
13878
13919
+0.30%
2.00%
0.28%
within noise
l2_hit/nsenc/65536
403200
403158
-0.01%
2.00%
0.05%
within noise
set/plain/65536
70129
70083
-0.07%
0.50%
0.00%
within noise
set/rel/65536
70923
70877
-0.06%
0.50%
0.00%
within noise
set/enc/1024
10829
10783
-0.42%
0.50%
0.00%
within noise
set/enc/65536
305975
305929
-0.02%
0.50%
0.00%
within noise
set/ns/65536
70331
70285
-0.07%
0.50%
0.00%
within noise
set/nsenc/1024
11050
11004
-0.42%
0.50%
0.00%
within noise
set/nsenc/65536
306137
306091
-0.02%
0.50%
0.00%
within noise
delete/plain/40
3787
3763
-0.61%
4.23%
0.37%
within noise
delete/plain/64
3780
3757
-0.61%
2.00%
0.99%
within noise
delete/plain/1024
3787
3741
-1.21%
6.97%
1.93%
within noise
delete/plain/65536
3993
3978
-0.35%
2.00%
0.69%
within noise
delete/rel/40
4404
4398
-0.12%
2.00%
0.73%
within noise
delete/rel/64
4407
4383
-0.56%
2.00%
0.76%
within noise
delete/rel/1024
4416
4398
-0.40%
6.83%
1.52%
within noise
delete/rel/65536
4612
4589
-0.50%
2.00%
0.62%
within noise
delete/enc/40
3939
3909
-0.78%
2.48%
1.18%
within noise
delete/enc/64
3733
3718
-0.40%
2.69%
0.36%
within noise
delete/enc/1024
3756
3743
-0.36%
4.24%
2.00%
within noise
delete/enc/65536
3971
3962
-0.22%
2.25%
0.16%
within noise
delete/parked256/64
3837
3822
-0.39%
2.00%
0.06%
within noise
delete/parked1024/64
3842
3827
-0.40%
2.00%
0.16%
within noise
oneshot/enc/40
69365
69436
+0.10%
0.50%
0.00%
within noise
oneshot/enc/64
69479
69550
+0.10%
0.50%
0.00%
within noise
oneshot/enc/1024
73153
73224
+0.10%
0.50%
0.00%
within noise
oneshot/enc/65536
462561
462632
+0.02%
0.50%
0.00%
within noise
oneshot/prev/40
101702
101773
+0.07%
0.50%
0.00%
within noise
oneshot/prev/64
101890
101961
+0.07%
0.50%
0.00%
within noise
oneshot/prev/1024
108442
108513
+0.07%
0.50%
0.00%
within noise
oneshot/prev/65536
792993
793064
+0.01%
0.50%
0.00%
within noise
macro_hit/plain/65536
99679
99642
-0.04%
0.50%
0.00%
within noise
macro_hit/rel/65536
99695
99658
-0.04%
0.50%
0.00%
within noise
macro_hit/enc/65536
336332
336226
-0.03%
0.50%
0.00%
PR head 48ada55026f787de338b97e5a30d716d7ef9b69d merged into its base, measured against 1691aa50faae09edac67dac01b25c4f09bed3f76 on the same runner. Workflow run
`interop_read_swr` awaited `SecureCache::__interop_read_swr` for an
encrypting client, so its state machine stored the whole secure read
future beside the plain read's locals. The `#[cachekit]` read's poll
function is generic and instantiated in the caller's crate, so any
change to the secure read reshaped the plain read's code: the plaintext
mark added 34 instructions per `macro_hit/plain` and `macro_hit/rel`
op, all of them moves of the resolved key in that poll function.
Both clients read the same bytes and differ only in the decode. The
read now awaits `read_bytes_swr` once and branches afterwards, and the
secure side becomes `SecureCache::decode_swr`, a synchronous decode, so
the future holds no part of the secure read.
Instruction counts against main (callgrind, 122 cases): every case
passes. `macro_hit/plain` and `macro_hit/rel` read 37 Ir/op faster
(-0.67% at 40 B), and `macro_hit/enc` 105 Ir/op faster (-1.08%). The
same change on main alone moves `macro_hit/plain` from 5508 to 5474,
and the mark then moves it to 5471: the plain read no longer depends on
the secure read's code.
…nch rule
decode_swr also decrypts, evicts on a failed tag and adopts the walk mark into L1, all through SecureCache::open, so name it for open. The comment in interop_read_swr now states the rule, not its history: the secure decode still runs in the shared poll function, and only an awaited secure future would sit in the plain read's state.
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An encrypted L1 hit decrypted its ciphertext and then ran cachekit-core's
msgpack_document_lenbounds walk on the plaintext on every hit, although the walk's verdict on that plaintext cannot change while L1 holds the same ciphertext. This PR walks it once. The first L1 hit whose decrypted plaintext passes the walk marks the L1 entry, and later hits on that ciphertext decrypt and then decode without the walk. An encrypted 20-field struct hit at 40 B goes from 15,170 to 12,733 Ir/op (−16.1%).How
Payload'swalkedflag becomesWalked { No, Bytes, Plaintext }.Payload::deserializer, the path of a client without encryption, honours onlyBytes. The newDecrypted::deserializerhonours onlyPlaintext. A mark one kind of decode earned is never trusted by the other. Ciphertext whose first byte is below0x80can itself pass the walk, so a single bool would be safe only for as long as every read path routes an encrypting client throughSecureCache.Payload::decryptkeeps the plaintext together with the ciphertext it came from, asDecrypted.Decrypted::deserializerrecords that its own walk passed.Decrypted::markedis the only way to build aPlaintext-marked payload, and it returns one only after that walk passed.Payload's fields stay private to the serializer module, so no other code can pair a mark with other bytes.L1Cache::adoptswaps the marked payload in under the shard's write lock (quick_cacheentry), and only if the entry still holds the sameBytesbuffer (pointer and length). A write, delete or eviction during the hit leaves L1 as it left it, and an absent key gains no entry. The read still holds a reference to the buffer, so its address cannot be reused while the two are compared. TTL and freshness are unchanged.l2_hit/enc.Why the same ciphertext always yields the same verdict
Every read still decrypts and authenticates. A client's keyring is fixed when it is built: the current key is tried first, then each previous key in a fixed order. The AAD binds the storage key the entry was read under, so the same ciphertext read for the same key either fails authentication or decrypts to the same plaintext. L1 is private to one client, and
Bytescannot be modified in place while L1 holds a reference to it. No backend can rewrite a marked buffer: every backend read returns a freshVec<u8>, and the copy a write hands the backend is an immutableBytes.How this differs from the bit cachekit-io/cachekit-py#671 declined. The mark is never stored, sent or read from any backend: it lives in this process's L1 entry and nowhere else. This process sets it only after its own decrypt and its own walk of the same immutable ciphertext pass. It records only that the plaintext parses within the decode bounds, which every successful read already shows. No AAD, key, nonce or wire byte changes.
Read paths
SecureCache::get(andCacheKit::geton an encrypting client)SecureCache::interop_getSecureCache::interop_get_swr, Fresh and Stale#[cachekit(secure)]reads (__interop_read,__interop_read_swr, Fresh and Stale)prev)nsenc)L1Cache::setInstruction counts
From
make bench-instr BASE=<base>: callgrind, median of 5 ABBA runs, release build with--features macros. The base ismainplus this PR's first commit, which only adds thel1_hit_row/enccase, so both builds run the same workload. The two binaries sat at paths of equal length. Cells inside the gate's noise floor say "noise".l1_hit_row/enc(new: a 20-field struct)l1_hit/enc(String)l1_hit/nsencmacro_hit/enc¹macro_hit/plain,macro_hit/rel¹¹ Measured at the head against
mainwithbench_hot_path instr --base, from another build of both binaries than the rows above, so their absolute counts differ. That run passes all 122 cases.l1_hit/plain,l1_hit_row/plain,l1_hit/prev,l2_hit/*andoneshot/*are inside their floors.set/*(−0.6% to −1.1%) andexists/*(−6.7%) read faster although this PR does not touch either path.A/A. A second build of the base source, from a different checkout of equal path length, measured against the base binary: all 120 gated cases are inside their floors. Only the ungated
deletecases flag, at a 7% run-to-run spread.macro_hit. The plain and secure#[cachekit]reads share one poll function, which is generic and so instantiated in the calling crate. An encrypting client's read used to await a secure read future stored inside the plain read's future, so the mark's change to the secure read added 34 Ir/op tomacro_hit/plainandmacro_hit/rel: moves of the resolved key, with no new code run. The read now awaitsread_bytes_swronce and branches afterwards toSecureCache::open_swr, a synchronous decrypt and decode. The same change onmainalone movesmacro_hit/plainat 40 B from 5,508 to 5,474, and adding the mark then moves it to 5,471, so the plain read no longer depends on the secure read's code.The trade: a key read once from L1 pays one
quick_cacheentrycall on its first hit. Every later hit on it saves the walk, about 2,400 Ir for the 20-field struct and 34 for a 40 B string.Tests
sealed_hostile_plaintext_fails_from_the_backend_and_every_time_from_l1: every reject vector of the protocol'sdecode-bounds.json, plus a 60-level recursive enum, is sealed under the client's own key and read by all five secure read paths. Each read is refused from the backend, from L1, and from L1 again. rmp-serde alone decodes the enum, so a wrongly set mark shows up as a successful read.every_sealed_accept_vector_decodes_from_the_backend_and_from_l1: the backend read, the hit that walks and marks, and the marked hit decode to the same value.an_own_encrypted_write_of_a_deep_recursive_enum_fails_from_l1_every_time, the encrypting twin of #214'san_own_write_of_a_deep_recursive_enum_fails_from_l1, which still passes.client::plaintext_mark_tests: an own write is unmarked until its first L1 hit; an L2 hit marks nothing and the next L1 hit marks; a passing walk marks even when the requested type does not fit; a mark never lands on a rewritten or deleted entry, and adds no entry; the publicL1Cache::setstays unwalked.make quick-checkpasses (690 tests).clippy --lib -D warningsalso passes withencryption,l1,l1,encryption,unsync,redis,memcachedandcachekitio,encryptionalone, and the wasm32workers,encryptioncheck passes.Docs
l1_hit_row'sencmode.MAX_DECODE_DEPTH,bounded_deserializer,Payload,Walked,DecryptedandL1Cache::adoptsay where the walk runs, which function mints each mark, and which decode honours it.Closes LAB-12915