The commitlog replayer groups segments by shard using a
std::unordered_multimap, then iterates per-shard segments via
equal_range(). However, equal_range() does not guarantee iteration
order for elements with the same key, so segments could be replayed
out of order within a shard.
Correct segment ordering is required for:
- Fragmented entry reconstruction, which accumulates fragments across
segments and depends on ascending order for efficient processing.
- Commitlog-based storage used by the strongly consistent tables
feature, which relies on replayed raft items being stored in order.
Fix by changing the data structure from
std::unordered_multimap<unsigned, commitlog::descriptor>
to
std::unordered_map<unsigned, utils::chunked_vector<commitlog::descriptor>>
Since the descriptors are inserted from a std::set ordered by ID, the
vector preserves insertion (and thus ID) order. The per-shard iteration
now simply iterates the vector, guaranteeing correct replay order.
Fixes: SCYLLADB-1411
Backport: It looks like this issue doesn't cause any trouble, and is required only by the strong consistent tables, so no backporting required.
Closesscylladb/scylladb#29372
* github.com:scylladb/scylladb:
commitlog: add test to verify segment replay order
commitlog: fix replay order by using ordered map per shard
8e7ba7efe2