Architecture Decision Records on Strata Documentation

ADR-0001: Skip RADOS omap for bucket index

Mon, 01 Jan 0001 00:00:00 +0000

ADR-0001: Skip RADOS omap for bucket index#

Status#

Accepted — April 2026

Context#

Strata is positioned as a drop-in replacement for Ceph RGW. RGW stores the bucket index in a small set of RADOS objects, each carrying an omap (ordered key→value map) that lists the bucket’s objects in lex order. The omap is convenient — listing is a native ordered scan — but it has hard scale ceilings:

The omap of a single index object lives in a single placement group. All listing traffic and all index mutations for that shard land on one OSD, capped by that OSD’s IOPS budget.
RGW’s only mitigation is bucket-index resharding (radosgw-admin bucket reshard). Resharding rewrites the entire omap, must quiesce or rate-limit write traffic during the cut-over, and the shard count tops out before the largest production buckets do — beyond roughly 100M objects a single bucket exhausts the resharding ceiling and starts taking IOPS hits regardless.
The contract is opaque to the layer above. We cannot trade consistency for throughput, partition by a different key, or fan out across heterogeneous storage tiers without re-implementing the scan path.

We considered (a) keeping omap with aggressive resharding and (b) moving the index to a separate ordered store. (a) inherits RGW’s ceiling; the project goal is to lift it, not match it.

ADR-0002: Derive IsLatest at read time

Mon, 01 Jan 0001 00:00:00 +0000

ADR-0002: Derive `IsLatest` at read time#

Status#

Accepted — April 2026

Context#

S3 versioning requires every object row to expose an IsLatest bit: the most recent (un-deleted) version of a key carries IsLatest=true, every older version carries IsLatest=false. The naive implementation flips the bit on the previous head whenever a new PUT lands — UPDATE objects SET is_latest=false WHERE bucket_id=? AND key=? AND version_id=<prev> immediately after inserting the new version row.

ADR-0003: Single manifest blob column

Mon, 01 Jan 0001 00:00:00 +0000

ADR-0003: Single `manifest` blob column for object metadata#

Status#

Accepted — April 2026

Context#

Per-object metadata in Strata is rich and growing: chunk OIDs, chunk sizes, MD5 / SHA256 digests, SSE wrap context, multipart part boundaries (PartChunkCounts, PartChunks), backend routing hints (BackendRef.Cluster), and several smaller fields. A normalised schema would dedicate one column per field, possibly with side tables for the variable-length arrays (chunks, parts).

The cost of normalised columns on Cassandra is two-fold:

ADR-0004: One leader lease per background worker

Mon, 01 Jan 0001 00:00:00 +0000

ADR-0004: One leader lease per background worker#

Status#

Accepted — April 2026

(Reconsideration tracked under ROADMAP ## Consolidation & validation. If the supervisor collapse lands, this ADR will be marked Superseded by ADR-XXXX.)

Context#

strata server ships roughly ten background workers — gc, lifecycle, replicator, notify, access-log, inventory, audit-export, manifest-rewriter, rebalance, quota-reconcile, usage-rollup. Each of them must run on at most one replica at a time: GC must not double-delete, lifecycle must not duplicate transitions, etc. Some shape of singleton election is required regardless of the deploy footprint.

Architecture Decision Records on Strata Documentation

ADR-0001: Skip RADOS omap for bucket index

ADR-0001: Skip RADOS omap for bucket index#

Status#

Context#

ADR-0002: Derive IsLatest at read time

ADR-0002: Derive IsLatest at read time#

Status#

Context#

ADR-0003: Single manifest blob column

ADR-0003: Single manifest blob column for object metadata#

Status#

Context#

ADR-0004: One leader lease per background worker

ADR-0004: One leader lease per background worker#

Status#

Context#

ADR-0002: Derive `IsLatest` at read time#

ADR-0003: Single `manifest` blob column for object metadata#