Key cache

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 (DD-MM-YY)
 
+## Unreleased
+
+- *Breaking:* Storage item key must now also be clone
+- Added KeyPointerCache which significantly helps out the map
+
 ## 0.8.1 07-02-24
 
 - Added new PagePointerCache that caches more than the PageStateCache. See the readme for more details.

README.md

@@ -73,11 +73,12 @@ Instead, we can optionally store some state in ram.
 
 These numbers are taken from the test cases in the cache module:
 
-|             Name |     RAM bytes | Map # flash reads | Map flash bytes read | Queue # flash reads | Queue flash bytes read |
-| ---------------: | ------------: | ----------------: | -------------------: | ------------------: | ---------------------: |
-|          NoCache |             0 |              100% |                 100% |                100% |                   100% |
-|   PageStateCache | 1 * num pages |               77% |                  97% |                 51% |                    90% |
-| PagePointerCache | 9 * num pages |               69% |                  89% |                 35% |                    61% |
+|             Name |                                    RAM bytes | Map # flash reads | Map flash bytes read | Queue # flash reads | Queue flash bytes read |
+| ---------------: | -------------------------------------------: | ----------------: | -------------------: | ------------------: | ---------------------: |
+|          NoCache |                                            0 |              100% |                 100% |                100% |                   100% |
+|   PageStateCache |                                1 * num pages |               77% |                  97% |                 51% |                    90% |
+| PagePointerCache |                                9 * num pages |               69% |                  89% |                 35% |                    61% |
+|  KeyPointerCache | 9 * num pages + (sizeof(KEY) + 4) * num keys |              6.5% |                 8.5% |                   - |                      - |
 
 #### Takeaways
 
@@ -87,6 +88,10 @@ These numbers are taken from the test cases in the cache module:
 - PagePointerCache
   - Very efficient for the queue
   - Minimum cache level that makes a dent in the map
+- KeyPointerCache
+  - Awesome savings!
+  - Numbers are less good if there are more keys than the cache can store
+  - Same as PagePointerCache when used for queue
 
 ## Inner workings
 

fuzz/fuzz_targets/map.rs

@@ -5,7 +5,7 @@ use libfuzzer_sys::arbitrary::Arbitrary;
 use libfuzzer_sys::fuzz_target;
 use rand::SeedableRng;
 use sequential_storage::{
-    cache::{CacheImpl, NoCache, PagePointerCache, PageStateCache},
+    cache::{KeyCacheImpl, KeyPointerCache, NoCache, PagePointerCache, PageStateCache},
     map::{MapError, StorageItem},
     mock_flash::{MockFlashBase, MockFlashError, WriteCountCheck},
 };
@@ -19,6 +19,7 @@ fuzz_target!(|data: Input| match data.cache_type {
     CacheType::NoCache => fuzz(data, NoCache::new()),
     CacheType::PageStateCache => fuzz(data, PageStateCache::<PAGES>::new()),
     CacheType::PagePointerCache => fuzz(data, PagePointerCache::<PAGES>::new()),
+    CacheType::KeyPointerCache => fuzz(data, KeyPointerCache::<PAGES, u8, 64>::new()),
 });
 
 #[derive(Arbitrary, Debug, Clone)]
@@ -101,9 +102,10 @@ enum CacheType {
     NoCache,
     PageStateCache,
     PagePointerCache,
+    KeyPointerCache,
 }
 
-fn fuzz(ops: Input, mut cache: impl CacheImpl) {
+fn fuzz(ops: Input, mut cache: impl KeyCacheImpl<u8>) {
     let mut flash = MockFlashBase::<PAGES, WORD_SIZE, WORDS_PER_PAGE>::new(
         WriteCountCheck::OnceOnly,
         Some(ops.fuel as u32),