**Specification:**
View spec at [this URL](https://git.deuxfleurs.fr/Deuxfleurs/garage/src/branch/k2v/doc/drafts/k2v-spec.md)
- [x] Specify the structure of K2V triples
- [x] Specify the DVVS format used for causality detection
- [x] Specify the K2V index (just a counter of number of values per partition key)
- [x] Specify single-item endpoints: ReadItem, InsertItem, DeleteItem
- [x] Specify index endpoint: ReadIndex
- [x] Specify multi-item endpoints: InsertBatch, ReadBatch, DeleteBatch
- [x] Move to JSON objects instead of tuples
- [x] Specify endpoints for polling for updates on single values (PollItem)
**Implementation:**
- [x] Table for K2V items, causal contexts
- [x] Indexing mechanism and table for K2V index
- [x] Make API handlers a bit more generic
- [x] K2V API endpoint
- [x] K2V API router
- [x] ReadItem
- [x] InsertItem
- [x] DeleteItem
- [x] PollItem
- [x] ReadIndex
- [x] InsertBatch
- [x] ReadBatch
- [x] DeleteBatch
**Testing:**
- [x] Just a simple Python script that does some requests to check visually that things are going right (does not contain parsing of results or assertions on returned values)
- [x] Actual tests:
- [x] Adapt testing framework
- [x] Simple test with InsertItem + ReadItem
- [x] Test with several Insert/Read/DeleteItem + ReadIndex
- [x] Test all combinations of return formats for ReadItem
- [x] Test with ReadBatch, InsertBatch, DeleteBatch
- [x] Test with PollItem
- [x] Test error codes
- [ ] Fix most broken stuff
- [x] test PollItem broken randomly
- [x] when invalid causality tokens are given, errors should be 4xx not 5xx
**Improvements:**
- [x] Descending range queries
- [x] Specify
- [x] Implement
- [x] Add test
- [x] Batch updates to index counter
- [x] Put K2V behind `k2v` feature flag
Co-authored-by: Alex Auvolat <alex@adnab.me>
Reviewed-on: Deuxfleurs/garage#293
Co-authored-by: Alex <alex@adnab.me>
Co-committed-by: Alex <alex@adnab.me>
With the previous behaviour, repairing could see some data as absent
and decide that the object or version was deleted,
thus going on to delete the version and blocks.
In the case where read_quorum + write_quorum <= replication_factor
however, entries may not yet be returned by the get, thus data would
have been deleted that should hot have been. The new behavior is more
cautious and just skips the entry when the warning is emitted.