Add split_key_prefix_len to index config to shard S3 object keys#6529
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Recent splits share a ULID timestamp prefix, causing S3 key hotspots under high read load. Setting split_key_prefix_len (e.g. 2) on an index extracts N characters from the ULID random portion (positions 10–25) as a subdirectory prefix, distributing new splits across 32^N S3 partitions. Old splits (prefix not set in SplitMetadata) continue using the legacy flat path; no migration needed. SplitMetadata will store a `prefix` string computed once at creation time via compute_split_key_prefix().
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Summary
split_key_prefix_len: u8toIndexConfig(andIndexTemplate) to configure S3 key sharding per indexcompute_split_key_prefix(split_id, prefix_len)toquickwit-common— extracts N characters from the ULID random portion (positions 10–25) as a prefix; logs a rate-limited warning and falls back to the flat scheme if the split ID is too shortsplit_storage_path(split_id, prefix)toquickwit-common— builds the storage path from a precomputed prefix string; empty prefix = legacy flat schemesplit_key_prefix_len <= 16(ULID random portion length) at config load timeSplitMetadatawill gain aprefix: Stringfield in a follow-up PR to wire the full pipeline (uploader, leaf search, merge, GC)Backward compatibility: the field defaults to
0(serde default), so all existing indexes and splits are unaffected. New splits on indexes withsplit_key_prefix_len: 2will land atND/01ARZ3.../01ARZ3....splitpaths, distributing across 1024 S3 partitions instead of one.Test plan
cargo nextest run -p quickwit-common -p quickwit-config --all-features— 221 tests passcargo clippy --workspace --all-features --tests— no warningscargo +nightly fmt --all -- --check— no issuessplit_key_prefix_len: 2in an index config, verify it round-trips through serde correctlysplit_key_prefix_len: 17, verify it is rejected with a clear error message🤖 Generated with Claude Code