[Drift] New S3 storage stats add per-sync-config Prometheus metrics (powersync-service #770)

[benitav]

What's changing: PowerSync Service now tracks storage statistics for S3-compatible object storage (used by MongoDB V3 storage), and exposes new Prometheus metrics attributing storage size and record counts per sync config, in addition to the existing global storage metrics.

High priority — existing docs are now inaccurate or incomplete
None identified. The existing metrics (replication_storage_size_bytes, operation_storage_size_bytes, parameter_storage_size_bytes) are unchanged by this PR.

For reviewer consideration — worth documenting

• New Prometheus metrics: powersync_object_storage_size_bytes (total object storage size) and four per-sync-config attribution metrics, powersync_attributed_source_records_bytes, powersync_attributed_bucket_data_bytes, powersync_attributed_parameter_indexes_bytes, and powersync_attributed_object_storage_bytes, each labeled by sync_config_id and sync_config_state. Usage Reporting (maintenance-ops/self-hosting/usage-reporting.mdx → https://docs.powersync.com/maintenance-ops/self-hosting/usage-reporting), "What is Collected" table, lists the currently reported metric dimensions but doesn't include these new ones.

Source PR: powersync-ja/powersync-service#770. Merged 2026-08-31.

Filed automatically by Claude Code (claude-sonnet-5). A human must verify the scope, prepare the docs PR, and publish it only once this update has been released.

[rkistner]

Can include this as part of a general "storage version 4" docs and/or announcement.

[benitav]

powersync-service#781 (merged 2026-09-01) extends the same feature this issue covers: it adds the sync config's version_label (added in #756/powersync-service#756) as an attribute on the per-sync-config storage metrics introduced by the PR this issue tracks, so operators can distinguish attributed metrics by deployed sync config version. The label is deliberately excluded from the shared OTLP telemetry PowerSync collects, avoiding the anonymity concern that would otherwise raise. No new page is affected: the already-cited Usage Reporting page (maintenance-ops/self-hosting/usage-reporting.mdx), "What is Collected" table, would need version_label noted alongside sync_config_id and sync_config_state once the attribution metrics themselves are documented.

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Generated by Claude Code

[benitav]

Will be resolved with #611